Knock sensors revisited

[Force Fed Mopar]

So, long story short, I did an immense amount of playing around with the knock sensor vs rpm table in the Lebaron, trying to find a happy medium between engine/combustion noise and accurate knock sensing to tune from last year, without much success. Pretty much ended up just about disabling it and going by ear/seat of the pants/educated guess work.

I am using a new knock sensor, but do not have Teflon tape on the threads. Is this causing it to be overly sensitive? I know many people have put it on theirs to keep it from being so, but was it that way from the factory? Is this a good way to make it usable?

I know also that the type our cars use is very primitive and designed with specific parameters in mind. Possible that at higher than stock boost and power levels that it's no longer useful at all? I have been told as much by some accomplished tuners on other sites. I do plan on making a wideband knock sensor setup (as has been described in other threads) for it to compare against, so I may be able to answer my own questions at that point.

[5DIGITS]

So, long story short, I did an immense amount of playing around with the knock sensor vs rpm table in the Lebaron, trying to find a happy medium between engine/combustion noise and accurate knock sensing to tune from last year, without much success. Pretty much ended up just about disabling it and going by ear/seat of the pants/educated guess work.
I am using a new knock sensor, but do not have Teflon tape on the threads. Is this causing it to be overly sensitive? I know many people have put it on theirs to keep it from being so, but was it that way from the factory? Is this a good way to make it usable? I know also that the type our cars use is very primitive and designed with specific parameters in mind. Possible that at higher than stock boost and power levels that it's no longer useful at all? I have been told as much by some accomplished tuners on other sites. I do plan on making a wideband knock sensor setup (as has been described in other threads) for it to compare against, so I may be able to answer my own questions at that point.

"...trying to find a happy medium between engine/combustion noise and accurate knock sensing to tune from last year, without much success."

What approach are you using to identify the different levels of background noise?

Thanks

[Shadow]

I've never understood the difficulty others have had with the factory knock sensors in these mtrs? I've used them from day one, as is and they've always worked Great for a factory piece! (except when they were bunk and needed replace that is)

I don't know where everyone is getting all of the sensitivity from? Typically I'll see .02-.04 fluctuation on the DRBII which I've just found to be normal operation. Then, IF the mtr starts to detonate the knock is going off way before I hear anything and the ECU is pulling timing to compensate. After that it will become audible.

I've always used and learned to trust them "as is" and run Zero knock tunes. Although I have had other built Turbo Mopar/ Dodges come into the shop that just wouldn't stop knocking and the owner had given up. Very rarely was it the sensor, but just a mix and mess of everything being put together poorly. (a jumble of parts bought off the net and bad advice from ppl who unfortunately don't know what they're talking about)

I'm starting to think it has a lot to do with ppl tuning their own cars and messing everything up in the ECU?

[Ondonti]

headphone setup is what I would do before ignoring noises or relying on your normal ears. Read plugs at least after a pull etc.

[Reaper1]

I'm curious where this goes. The tune I got from Rob (ShelGame) for my Z was great! It ran much better than the other tune I had, especially in the mid range and part throttle. I had him include the CEL knock detection in that tune. No matter what I did the CEL would always flash at me under boost. I tried lower boost, adding fuel, different fuel, adding water/meth injection, adjusting the timing, and putting Teflon tape around the threads. Nothing ever made it better (or worse, just to be clear). I never did get around to changing out the sensor. IIRC Rob did tell me that the MOPAR knock sensor was better to get and could absolutely be relied on compared to a "parts store" version. Now, knowing what I do about "parts store" parts, depending on the manufacturer (usually Wells), they are the same part you would get at the dealer. However, I do also know that sometimes the OEM versions of the parts hold a tighter tolerance or are built to specific specs where as the aftermarket versions are more generic.

The question whether the engine in my car was actually experiencing knock all those times is debatable. The plugs never indicated it. When I popped the headgasket, though, the gasket itself showed signs of higher than normal temps/pressures, #3 piston had a small amount of pitting, and the rod bearing had a touch more wear on the top shell compared to the bottom shell. The thing is I can't say for certain whether that happened when I popped the gasket, or from some other time in the past.

The long block of that engine was completely stock. It made no noise, so piston slap or something like that is out of the question (or it should be).

An overly sensitive knock sensor can be just as bad as a broken one, or not having one, especially when tuning. I am very curious how to filter out background noise, though. From what I understand this would be like a bandpass filter because knock normally produces a certain small range of frequencies. That range is mostly defined by the design of the engine (I think bore size has something to do with it).

Ken, I am VERY interested in hearing your expert input on this. I remember you going over it at a SDAC tech session, but that's been a long time ago. :thumb:

[shackwrrr]

I had to disable mine below 3k rpm. but I have loose fitting forged pistons. My timing is dead flat 0 degrees over 5 Psi of boost but I still get cel flash sometimes. If I push it I get audible knock and when its cold out it gets much worse.

[Shadow]

I had to disable mine below 3k rpm. but I have loose fitting forged pistons. My timing is dead flat 0 degrees over 5 Psi of boost but I still get cel flash sometimes. If I push it I get audible knock and when its cold out it gets much worse.

Something seriously wrong there. I'm surprised how many drive around with motors that have audible knock and can't figure out the problem.

[Force Fed Mopar]

What approach are you using to identify the different levels of background noise?

Thanks

At first I copied the MP Stage 2 LM table, but it was for a 2.2, so then I went to the 2.5 MP Mtx table. At 10-12 psi on stock 2.5 MP timing tables it seemed okay, but over that it would set the light off. I was fairly sure that at 15 psi it wasn't detonating, so I just bumping up the knock threshold until I didn't see the CEL flash anymore at that boost level when it spooled up. That seemed good except that it would flash on above 4500, so then I bumped it up some more above that. That worked fine, until I went up to 18-20 psi, then I had to do it all over again.

Now at this point the threshold is way higher than stock. Maybe not a big deal, maybe it is a big deal? Every so often it will flash on a normal acceleration shift too, no boost, just run it up to 2500-3k and shift and it'll blink on a sec, so I move it up a little in the lower rpm area also.

I have Wiseco pistons w/ about .004" clearance, and stock original valve springs and 2.4 lifters (the ones with the bleed hole in the nose) properly shimmed. New knock sensor, no tape on the threads. Stock head, stock valves, stock cam, stock 2-piece, 52mm TB, water-to-air intercooler, stock T2 turbo, ported exhaust manifold, 2.5" sv, 3" exhaust. Ran 80 mph in the 8th on street tires. Car weighs 3300 with me in it. 568 trans, 3.77 gear.

Here's my current knock table compared to the stock MP 2.5 Mtx table (green line).

49343

[zin]

I'd also install a "det can"/headphones before disregarding a knock sensor... now that I have a workable soldering iron, maybe I'll put together my electronic version, got high hopes for it.

Mike

- - - Updated - - -

I'd also install a "det can"/headphones before disregarding a knock sensor... now that I have a workable soldering iron, maybe I'll put together my electronic version, got high hopes for it.

Mike

[Ondonti]

I'd also install a "det can"/headphones before disregarding a knock sensor... now that I have a workable soldering iron, maybe I'll put together my electronic version, got high hopes for it.

Mike


Yeah, a lot of stress over something that you can 100% prove with a headphone setup. I have tried this even in a bone stock car and recorded the audio and then spectrogram'd it. Knock stands out, especially when you can hear it over the exhaust. Trying to identify knock without listening to it is like a blind man trying to learn sign language. Once you get the audio to match up with your knock sensor behavior, you know you are on track.

[Force Fed Mopar]

Also, here is my current WOT Timing from Map table. The red line is stock MP 2.5, the blue and green lines are what I've tried and it would set the light off either way. The stock one flatlines after 15 psi so I can see why it would knock above that. The blue I just basically continued the slope, the green is where I pulled a bunch of timing out trying to get it to not show knock.

49344

[shackwrrr]

Here is a copy of my Cal, if you open it up you can see that I have less timing than factory at 15psi and my knock voltage scale is raised significantly. I still get random flashes and audible knock. Rob M. do you ever get audible knock?

[Force Fed Mopar]

Here is a copy of my Cal, if you open it up you can see that I have less timing than factory at 15psi and my knock voltage scale is raised significantly. I still get random flashes and audible knock. Rob M. do you ever get audible knock?

Only on the stock MP timing and at more than 15psi.

I assume you have a new sensor also?

[Force Fed Mopar]

My 2 main problem areas with knock were right when it spooled fully (about 3k), and then above 4500. I did try pulling timing from those points in the Timing from RPM table also. It just always seemed to get slower the more I fooled with it, always just ended up going back to what I have now, or close to it.

[5DIGITS]

As indicated within the thread, this area of calibration does not typically require excessive effort and recalibrating the knock sensor should not be considered an approach to mask mechanical issues or support increased spark advance.
But for those who are interested in gaining additional information, the following steps can help identify what the levels are and where the peak values are realized.

The production knock sensor calibration values were set to avoid any and all audible knock, for customer satisfaction purposes.
This also includes an effort to preserve the head gasket, avoid dealership repair downtime, and the resulting warranty costs.
The result has the spark reduction process somewhat hyperactive and over-sensitive even in the stock configuration.
Considering that many of the vehicles on the forum are modified, the challenge becomes understanding how the modifications have affected the mechanical and combustion noise levels, relative to the knock sensor.
This is where a CAS (Combustion Analysis System) would be very useful but without it there are a couple ways to understand the back ground/operational noise levels, specific to your vehicle.

Considerations:
The engine should be in good mechanical condition, for obvious reasons.
Please make sure all engine and sensor grounds are intact and the controller is free of any faults that would alter the results.
High output ignition systems can impact the sensor noise levels - consider testing with and without.
Confirm that the injectors metal body do not contact/touch any portion of the intake manifold.
When this occurs, the injector will transfer its mechanical noise into the intake.

Getting started...
Considering that combustion noise will vary as a function of load/MAP and the mechanical noise is best identified with minimal cylinder pressure, we can attempt to isolate them and determine a general baseline for each.
The following steps are best completed while monitoring/recording engine RPM, MAP, and knock sensor voltage, via any safe means possible.
Again, this is far from combustion analysis but it can provide added insight, for those who are interested.

Mechanical Evaluation :


Retard spark advance via the distributor or in cal (for DIS) by 4-6 degrees throughout all operating conditions
(Depending how much spark advance is being used, this reduces the opportunity for detonation while testing)
With a warm engine, start at the lowest possible throttle angle/load, record the knock sensor voltage while slowly increasing the engine RPM from 1000 to the safest peak RPM
Decelerate the engine slowly, to avoid rapid low-load engine unwind
Let the engine idle for several minutes to de-aerate the oil and minimize any resulting valve-train/piston noise
Repeat the data collection process and confirm consistency with each previous run
These steps should not exceed ten (10) inches of vacuum, to remain at minimum cylinder pressures
At this point, a 'general' mechanical baseline has been identified, as seen by the knock sensor
If there's interest, a test can also be done between 2500-3500RPM while dithering the throttle
This induces varying combustion chamber pressure levels which excites wrist-pin and piston slap noise

The mechanical traces should be fairly consistent producing essentially a single knock sensor voltage curve, for the narrow MAP range used.


The next steps duplicate the previous process but introduces load.
The load intervals should be selected based on what you're willing to repeat up to elevated boost levels.
(For example: 2.5, 5, 10, 15psi, increments etc... )
This typically requires dragging the brakes under elevated torque conditions - USE CAUTION !

Combustion Evaluation :


Retard spark advance via the distributor or in cal (for DIS) by 4-6 degrees throughout all operating conditions
(Depending how much spark advance is being used, this reduces the opportunity for detonation while testing)
With a warm engine, start at atmospheric load, record the knock sensor voltage while slowly increasing the engine RPM from 1000 to the safest peak RPM
Let the engine idle for several minutes to de-aerate the oil and minimize any resulting valve-train/piston noise
Repeat the data collection process at the selected load to confirm run to run consistency
With repeatable results, increase the load to your next chosen level and repeat the previous steps
Considering the testing process, repeat the above steps only to a peak boost level that your comfortable with
At this point, the impact of increased cylinder pressure is identified as the growth of knock sensor voltage that exceeds the previously recorded mechanical results


The load based knock sensor curves will elevate as MAP increases but they don't always increase at the same rate between the tested boost levels.
This is the reason for collecting multiple load results and this should be considered when determining the knock table voltages for boost levels beyond the test levels.

I hope this helps and enjoy.

[Force Fed Mopar]

Helps very much, thank you! I had done some of this testing you describe, such as revving the engine in neutral under as light of throttle input as possible to get to max rpm and watch for the knock light. Did a little logging with MP Scan but not enough apparently;) I think I will throw out what I have and start back stock again. I do have an EBC now also, which doesn't allow it to spike boost as bad as the G-valve I had on it. So it should be easier to verify the knock levels as well as tune each boost level properly.

[5DIGITS]

The method of using the CEL to indicate knock was brought up earlier in the thread and its connection to the knock sensor calibration table is worth discussing.

Essentially there are two methods to support CEL illumination when knock is suspected.
The first is the old and currently used method of activating the light when the knock sensor voltage exceeds the voltage values calibrated in the knock sensor table.
Although this does work, its increased sensitivity while using a single input condition allows the light to illuminate during erroneous single low-level 'burst-knock' events, noise spikes, and/or with mechanical influence.

The second uncommon method is an approach that relies on the controllers determination of actual knock by illuminating the CEL based on multiple input conditions.
The multiple input determination helps minimize the erroneous events by only illuminating the light when realistically necessary.
Knock sensor voltage levels that exceed the knock calibration table value, knock events determined as something more than noise, and knock retard of any amount impact the determination.

What's common in both methods:


The opportunity for the driver to make a corrective decision to back out of the throttle or take their chances
Dependency on the knock sensor calibration table accuracy
Nearly immeasurable differences in controller determination time


What's different in the second method:


Ability to predetermine the legitimacy of actual knock occurrences
Minimized erroneous CEL illumination
Reduced tendency to modify the table to dangerous levels that nearly numb knock detection


The initial use of the CEL for knock detection came up in during the race days of the 2.2 race programs.
Coincidentally, the same approach was used with a fuel rail mounted sensor to turn on the CEL when fuel pressure dropped while cornering, due to pump cavitation.


When things are done properly in the controller, backing out of the throttle is no longer needed and the use of the CEL for knock indication is reduced to 'an event occurred but it's been handled'.

"Stay Tuned" and Enjoy

[John B]

I have the knock sensor trigger my check engine light, and it comes on when I hit a pot hole.

[ShelGame]

Ken, the current implementation of the CEL knock indicator is that the light comes only when the ECU is retarding timing due to knock. IE, any one of the 4 knock retard values is greater than 0. Knock retard is ignored below a set coolant temp (to reduce cold false knock).

So, its not just simply looking at the threshold.

[wallace]

Have you guys tried using higher octane fuel to see if this reduces or eliminates the knock? I have had 2 problems that were not knock cause the cel to flash. I traced one to bad alternator bushings and the cel went away. The second was knock on light load when engine was not up to operating temp. This second I believe was a rod bearing on its way out...I haven't taken the engine apart to see but I believe it spun while being flogged. With mpscan can we see which cylinder is detonating in the log?

[ShelGame]

Have you guys tried using higher octane fuel to see if this reduces or eliminates the knock? I have had 2 problems that were not knock cause the cel to flash. I traced one to bad alternator bushings and the cel went away. The second was knock on light load when engine was not up to operating temp. This second I believe was a rod bearing on its way out...I haven't taken the engine apart to see but I believe it spun while being flogged. With mpscan can we see which cylinder is detonating in the log?

Yes, MP Scan can log all 4 individual knock retards so you can see which cylinder is knocking.

[5DIGITS]

Ken, the current implementation of the CEL knock indicator is that the light comes only when the ECU is retarding timing due to knock.
IE, any one of the 4 knock retard values is greater than 0.
Knock retard is ignored below a set coolant temp (to reduce cold false knock).
So, its not just simply looking at the threshold.

I agree - the production minimum temp for knock reduction will definitely work to reduce false CEL triggers.
How many coded versions/variations are presently available and are there additional parameters being monitored, beyond the knock cells greater than zero?

The concern then becomes understanding how the following comment occurs.

I have the knock sensor trigger my check engine light, and it comes on when I hit a pot hole.

In other words, if a knock cell has a value stored; the CEL is illuminated until all the cells decrement back to zero.
This event can be greatly extended if the return rate to normal spark advance has been changed to an improper value.
This can also generate the impression that knock is still active even though it is not.
As previously mentioned, when additional required conditions (knock sensor voltage currently above the threshold, active retard, etc...) are monitored, then the CEL is illuminated only when legitimate knock is actually occurring.

[Force Fed Mopar]

All my testing has been done on 93 octane.

[ShelGame]

I agree - the production minimum temp for knock reduction will definitely work to reduce false CEL triggers.
How many coded versions/variations are presently available and are there additional parameters being monitored, beyond the knock cells greater than zero?

The concern then becomes understanding how the following comment occurs.


In other words, if a knock cell has a value stored; the CEL is illuminated until all the cells decrement back to zero.
This event can be greatly extended if the return rate to normal spark advance has been changed to an improper value.
This can also generate the impression that knock is still active even though it is not.
As previously mentioned, when additional required conditions (knock sensor voltage currently above the threshold, active retard, etc...) are monitored, then the CEL is illuminated only when legitimate knock is actually occurring.

I see your point. Currently, all of the CEL illumination code is exaclty the same; in the cals I have posted.

Adding a criteria to check the knock thrshold as well is easy, and I think it's a good idea.

In my experience, the knock indicator works well as-is (only from knock retard > 0). On the SMEC anyway, the factory knock retard decay is fast enough to make it very effective.

[Force Fed Mopar]

Is it possible that the forged pistons add more operational noise even when warm? I have to say though that I have watched the voltage some and it doesn't seem to pick up anything except in boost or on shifts in a certain rpm range.

[tryingbe]

Am I the only one that driving around with a scanner? I look for knock voltage and retard when the light flashes.

http://www.thelostartof.net/tryingbe/dodge/omniproject/heatsoak.jpg

[wallace]

Is it possible that the forged pistons add more operational noise even when warm? I have to say though that I have watched the voltage some and it doesn't seem to pick up anything except in boost or on shifts in a certain rpm range.

I would say that they would add additional noise compared to a stock cast piston. I think a test with higher octane fuel would give you an idea as to whether or not the knock is real or related to some other noise present. If the knock is reduced significantly or eliminated then it really is detonation if not then I would look at finding the source of the noise and eliminate it

[5DIGITS]

I see your point. Currently, all of the CEL illumination code is exaclty the same; in the cals I have posted.
Adding a criteria to check the knock thrshold as well is easy, and I think it's a good idea.
Thanks and I agree - this one is simple.


In my experience, the knock indicator works well as-is (only from knock retard > 0).
On the SMEC anyway, the factory knock retard decay is fast enough to make it very effective.

Rob, I agree 100% that there are many things in the code/calibration that work fairly well as is.
But whether they need it or not, having an adjustment 'knob' permits change.
The challenge for everyone is knowing when they need to change and to what values.
An example for requiring change is the use of a G-Head on later electronics and may lead to a cut and paste of the early cal values, from a 1985 Turbo-I.
Although, with head milling and discontinuity between the early and later style single/two-piece intakes or fabricated intakes means the older T-I values may not apply.
These conditions will affect the increment rates, decrement rates, long term knock constants and tables, and the knock sensor threshold table that triggers it all.
With this, an indicator for things heading in the wrong direction is disabling the use of long-term knock.
Rather, this should be a nagging question that asks "Why is the controller always trying to retard (de-rate) timing to a lower value spark table?" so the real problem can be addressed.
This is why "When things are done properly, backing out of the throttle is no longer needed and the use of the CEL for knock indication is reduced to 'an event occurred but it's been handled."

Once again, I applaud your efforts and always enjoy a good technical discussion - great thread !

EnJoy !

[Shadow]

Am I the only one that driving around with a scanner? I look for knock voltage and retard when the light flashes.

http://www.thelostartof.net/tryingbe/dodge/omniproject/heatsoak.jpg

Not the only one! lol I use a scanner on ever car I tune. Once tuned with zero knock I find no reason to monitor knock any further. Run the right fuel, Don't mess with Anything, and everything remains Safely tuned.

Only issues I've run into; Some people can't leave well enough alone and just have to mess with stuff. (mostly because of what they read on the forums)

For this reason I started installing knock lights in some cars..........

The Charger has never had any knock gauge or anything to monitor knock that remains in the car. Last time I checked the tune for knock was probably 4 years ago, but as some have said, I run the best race fuel I can nowadays. That, along with reading plugs on a regular basis, and there's really no reason to monitor knock unless something is changed.

[5DIGITS]

Not the only one! lol I use a scanner on ever car I tune.
Once tuned with zero knock I find no reason to monitor knock any further.
Run the right fuel, Don't mess with Anything, and everything remains Safely tuned.
Only issues I've run into; Some people can't leave well enough alone and just have to mess with stuff. (mostly because of what they read on the forums)
For this reason I started installing knock lights in some cars..........
The Charger has never had any knock gauge or anything to monitor knock that remains in the car.
Last time I checked the tune for knock was probably 4 years ago, but as some have said, I run the best race fuel I can nowadays.
That, along with reading plugs on a regular basis, and there's really no reason to monitor knock unless something is changed.

Thank you - Very well said !

[Force Fed Mopar]

So then basically I am probably running the limit of 93 octane on a 2.5, hence why the light always seems to be on above 12 psi, with all values set to stock? FWIW I ran 20 psi on my 2.2 Daytona without these issues, using the same exact top end and knock sensor. Only difference being 2.2 cast piston and 2.5 forged piston, and the 2.2 was on a large fmic, the 2.5 is on a awic. Also the 2.2 had a stock exhaust manifold, and on the 2.5 I ported it. AFR is 11-11.5 under WOT.

[5DIGITS]

So then basically I am probably running the limit of 93 octane on a 2.5, hence why the light always seems to be on above 12 psi, with all values set to stock? FWIW I ran 20 psi on my 2.2 Daytona without these issues, using the same exact top end and knock sensor. Only difference being 2.2 cast piston and 2.5 forged piston, and the 2.2 was on a large fmic, the 2.5 is on a awic. Also the 2.2 had a stock exhaust manifold, and on the 2.5 I ported it. AFR is 11-11.5 under WOT.

When you say "all the values" does that include fuel, spark, and knock sensor cals?
What are your EGT's currently at ?

[Force Fed Mopar]

When you say "all the values" does that include fuel, spark, and knock sensor cals?
What are your EGT's currently at ?

I don't have an EGT gauge, just an AEM wideband AFR monitor. Fuel is scaled for +40's and is 11.0-11.5 at WOT at any boost level. Spark tables being stock except for continuing slope after 14psi (where the stock tables flatline when you scale for 3-bar map). Knock tables being stock MP values. at 14-15 psi or higher with these settings, it would always set the CEL off at WOT. Normal light boost acceleration would be fine, moderately heavy part throttle acceleration would set it off sometimes. At the time I did not have a scanner or a laptop with a good battery so I couldn't look at the knock retard.

[Force Fed Mopar]

This is a stock MP 2.5 MTX cal, scaled for 3-bar and +40's, no other mods. It will flash the CEL for knock above 12 psi in my car, guaranteed, and it is audible.

[Force Fed Mopar]

This cal is based off the MP 2.5 MTX cal, but with highly modified knock threshold and the spark tables have the slope continued after 14psi instead of flatlined. Also the MultiplerOnMapAdvance has been flattened out. Seems like Rob L. recommended this for tuning the timing tables, but maybe I misunderstood him.

[Reaper1]

Am I the only one that driving around with a scanner? I look for knock voltage and retard when the light flashes.

http://www.thelostartof.net/tryingbe/dodge/omniproject/heatsoak.jpg

I'd love to have a scanner...just never could afford one when they'd pop up.

[wowzer]

fwiw - mpscan will log all those variables and more ..... and you could use your android phone if you want. so if you are already setup to burn tunes there is no additional cost for scanning. and actually i have been working on implementing the drb sensor/relay tests also.

sorry - off topic comment finished.

[shackwrrr]

maybe 2.5s want more fuel, stock at 15psi is running around 10:1 isn't it?

[5DIGITS]

maybe 2.5s want more fuel, stock at 15psi is running around 10:1 isn't it?

The current concern is the use of a stock 'fast-burn' head, slightly milled, at 18+ psi.
The fastburn head is already susceptible to knock, due to the lack of squish/quench, and without any chamber mods or bowl work the pressure rise at 18+ psi is violent.
When the pressure curve is short with high amplitude, the burn rate becomes an essential spike.
This leaves very little room for 'normal' spark advance and is shortened even further when combined with elevated boost levels.
In short, the burn rate determines how much spark can be tolerated and exposes why there is such a significant difference between the blastburn and previous G-head spark curves.

[5DIGITS]

With permission, I am providing the following discussion from a PM exchange that has been going on per this threads topic.
Hopefully this information may also be foudn useful by someone else.




I will check that. Would be worth going to an upgrade spring, or should I just stick with the stock roller springs? If I understand correctly from reading tech threads on places like Speedtalk, you only want as much spring as is needed to properly control the valve at maximum rpm and boost. Any more than that and you are just creating additional rotating friction which takes more power for the crank to turn.

Absolutely true !



It is a completely stock 782 swirl head, stock valve size, no porting, edge beveling or gasket matching at all.

This is the problem.



So what you're saying is that the swirl design swirls too much at higher boost levels? What does this cause?

In part but yes.
The head does not provide adequate squish.
This is the event that occurs as the piston approaches TDC.
The gases are squeezed between the outer diameter of the piston and the deck surface of the head, towards the center of the combustion chamber.
This does two things - compresses the remaining charge and increases localized charge density and forces any residual unburnt fuel into a reduced volume to extend the burn process.
Both of these events suppress knock and the fast burn falls significantly short in supporting this process.



Uneven combustion?

Yes, this is also part of the problem.
The gases that are permitted to linger between the plug and the intake valve provides a non-centralized burn, in a horse shoe shape.
Conceptually speaking, this allows the burn to collapse into each other and colliding flame fronts cause knock.


All my problems do seem to be much worse above 14 psi. 10 psi was no problem, 12 and 14 psi needed a little tweaking IIRC, and once I start running 15 and above it gets exponentially harder to avoid the CEL illuminating due to knock retard.

Exactly - As mentioned early on, the hardware arrangement will work well up to 13-14psi.
After that, the returns/power gains are over-shadowed by the need to greatly reduce spark advance.
Therefore, approx. 30HP is gained by raising boost from 10-13psi but raising the boost from 13-17psi only nets 10hp.
Peak efficiency and acceptable operating conditions have been exceeded.

BTW
I'm convinced that this is also the cause for your head gasket leak - the cylinder pressures can double during knock.
Don't bother milling the head again.
Replace the gasket and lower the boost to 14psi or less.

[Force Fed Mopar]

So the fast-burn head basically trades off power potential for greater efficiency, and as such only works well up to a certain level of combustion pressure?

[wallace]

So the fast-burn head basically trades off power potential for greater efficiency, and as such only works well up to a certain level of combustion pressure?

I would add the octane of the fuel you are running. The swirl and tumble designs are not exclusive to the 2.2/2.5. The swirl design provides a similar function of the tumble port without using a squish pad. The trick is to try and retain the swirl at elevated power levels. That's where the head porter can make a difference...or some kind of octane enhancement or both.

[86TSiGuy]

Wow, really enjoying the part of this thread on combustion chamber efficiencies. I'd like to add for what it's worth that there are other external variables that can influence detonation as well. Such as the presence of engine oil in the chamber, either from the intake or through the valve, and humidity. It is possible to tune a car on a humid day and experience knock with the same tune under dramatically less humidity.

[5DIGITS]

I would add the octane of the fuel you are running.
Octane will buy back spark advance and suppress knock but effort to corrective the main issue(s) will minimize the need.



The swirl and tumble designs are not exclusive to the 2.2/2.5.
The swirl design provides a similar function of the tumble port without using a squish pad. .

Although, a head design to either include or omit squish and the intakes bowl/port to induce swirl are not mutually exclusive.
In other words, if the material is filled in on the long side of the intake valve within the chamber (to gain additional squish for knock suppression) most if not all of the swirl can still exist and be retained.
With the 782, the lack of combustion chamber squish is the most significant contributor to knock.



The trick is to try and retain the swirl at elevated power levels.
That's where the head porter can make a difference...or some kind of octane enhancement or both.

Again, the fastburn came in as an emission and idle/mid throttle quality improver but its introduction made it a challenge to reach the previous year Turbo-I rating numbers.
Even though the need for combustion chamber swirl is reduced on forced induction vehicles, for obvious reasons; a conscious porting effort can retain whats needed to provide pre-boost throttle response.
This includes decent port velocity and good flow throughout the valve lift range (not just peak) but neither depends on swirl, to be successful.

[5DIGITS]

Wow, really enjoying the part of this thread on combustion chamber efficiencies.
I'd like to add for what it's worth that there are other external variables that can influence detonation as well.
Such as the presence of engine oil in the chamber, either from the intake or through the valve, and humidity.
It is possible to tune a car on a humid day and experience knock with the same tune under dramatically less humidity.

These details are excellent points - well said !!!!

[Force Fed Mopar]

Also, from what I understand, "swirl ports" and "fast burn chambers" do not need each other to be in a design. For instance, the 302 casting 318 heads and our 782 "swirl" heads, do not actually have "swirl ports" as I understand it. They only have fast burn chambers that induce swirl when the intake charge flows in. If you look at them you can see this, as the ports are essentially the same as "non-swirl" heads.

On the other hand, the 5.2/5.9 Magnum heads do have a swirl port design in them, as well as a fast burn chamber.

Again, this is only what I have understood from reading in various places, if I am wrong please correct me!

[5DIGITS]

Also, from what I understand, "swirl ports" and "fast burn chambers" do not need each other to be in a design.
For instance, the 302 casting 318 heads and our 782 "swirl" heads, do not actually have "swirl ports" as I understand it.
They only have fast burn chambers that induce swirl when the intake charge flows in.
If you look at them you can see this, as the ports are essentially the same as "non-swirl" heads.
On the other hand, the 5.2/5.9 Magnum heads do have a swirl port design in them, as well as a fast burn chamber.

Again, this is only what I have understood from reading in various places, if I am wrong please correct me!

True.
The 782's contribution to motivate swirl is achieved by having the intake port bowl area (on the long side) substantially filled in.
Remove that material and the resulting swirl will be eliminated.
Fixing the chamber... that's a bit more involved.

[Force Fed Mopar]

Well this has turned out to be a very helpful thread! Thank you very much for all the insights, I think I have a much better grasp of things now and will be working on re-doing my cal here shortly. I think I will start another thread shortly on what would be involved in fixing the swirl head :)

[Ondonti]

I'd love to have a scanner...just never could afford one when they'd pop up.

Use mine. I have no real use for it besides diagnosing something once a year on my cars that still have oem ecu.


To the head differences, a fastburn head should still be able to make decent power no matter how "against the odds things are" but if something has an extremely fast pressure rise that means the spark timing window is very small. That means you can't just "get it close." Its possible that adding 1 degree of timing puts you into knock and 1 degree less is a huge loss of power. Other setups can have a huge window of timing where it seems to make no difference but you still don't knock either. A more finicky combustion chamber is going to have even greater benefits on the dyno with a professional at the helm who knows how to get the most while not going too far.

[zin]

I'm thinking I'll have a head welded up to allow a "blank slate"... any suggestions as to an "ideal" turbo combustion chamber Ken?

I like Yates, but, much like we've seen on heavily nitroused engines, such a fast /efficient chamber may be a hindrance at higher HP levels.

Since this will obviously be more experiment than the average set-up, I'm also thinking I'd do a raised runner, up to the limit of the valve cover gasket surface, if going there is of benefit... I'm just not sure where to "steer" the mix past the valve, seems like some swirl would be in order if just to keep it from "crashing" into the cylinder wall...

This may be (probably) a 2.0l engine.

Mike

[ShelGame]

Ken - Maybe you have some insight into a question that's been bothering me for a while.

A G-Headed 2.5 is very difficult to tune. Too much timing and it knocks (seems to handle more timing than a FB head, though), too little timing and the EGT's soar; and performance drops dramatically.

What is it about the G-Head + 2.5l combination that makes it so difficult?

[Force Fed Mopar]

I think the increased piston speed is what makes it harder to tune in general, regardless of which head is used. Basically it is just a 2.2 with a stroker crank. However, while I know that it has an effect on timing, I've never been able to get a good answer on what effect it has. I have posted about it on Speedtalk before using a V8 stroker as an example (ie stroking a 318 to 390 w/o changing heads, intake or cam), but nobody really gave me a definitive answer, some even said it wouldn't change. I guess it's fairly rare to stroke any engine w/o changing something else at the same time.

[Reaper1]

I think it is fair to say that the 782 head has some definite improvements that can be made to it, however there is more than 1 side to a combustion chamber. A combustion chamber is a volume. In our case we can change the ceiling and the floor. The ceiling is the head. The floor is the piston. Since I learned about quench, swirl, tumble...all that good stuff, the mismatch of the pistons to the heads for our engines has bothered me...a LOT. A large part of the reason the 782 head is "crappy" is because it really isn't being used to its full potential. There is a quench pad, but the piston crown does not match it, so it isn't used. The dish in the piston allows the charge to go off in a direction away from the spark plug. On top of that, the piston crown does nothing to support the continuation of swirl. It's just a "bucket". To me, if there was a proper piston made to work with the head design, I'm pretty confident that there would be gains in all kinds of areas.

Ken, on the filling of the long side of the intake port in the bowl, I seem to remember that there is a very slight offset on one side of the bowl. From reading what others have said over the years, and seeing the work of people that really know what they are doing with that type of port work, I was under the impression that that was part of what starts the swirl of the charge. The rest is directed by the chamber shape (and to some extent the valve and valve seat). I agree that filling the long side would certainly help, but it's important to note that it's not just an arbitrary filling.

[roachjuice]

I don't even run one anymore. Flashing for no dam reason all the time. I set the timing to factory and run 15psi. It's held up for a month so far.

[Force Fed Mopar]

I don't even run one anymore. Flashing for no dam reason all the time. I set the timing to factory and run 15psi. It's held up for a month so far.

Well that's what 5DIGITS saying, is that the swirl head will work good up to 14-15 psi, after that it gets really sensitive to knock and require a lot of timing to be pulled to keep it from doing so. The chamber isn't designed to work well at higher boost levels.

[5DIGITS]

Ken - Maybe you have some insight into a question that's been bothering me for a while.
A G-Headed 2.5 is very difficult to tune. Too much timing and it knocks (seems to handle more timing than a FB head, though), too little timing and the EGT's soar; and performance drops dramatically.
What is it about the G-Head + 2.5l combination that makes it so difficult?

Trapping efficiency, piston dish OD, and piston speed (elevated piston temps) are all contributing factors.

Trapping efficiency:
Trapping efficiency is higher on the 2.5L that it is on the 2.2L which equates to higher cylinder pressures.
Working with higher cylinder pressures in turn has an effect on the amount of spark advance that can be used.
The quote listed below is posted on the Allpar website.

Dyno tester Ed Poplawski (http://www.allpar.com/corporate/bios/ed-poplawski.html) wrote,
“I worked on this a little bit. We ran Fast Burn heads on the 2.5L and the big advantage that I remember was that with the Fast Burn head, wide open throttle spark timing was lower than with the standard head, so you didn’t have to worry about spark knock too much and you didn’t need premium fuel. That made a big difference for the turbocharged engine.”

While it states that the spark reduction was largely due to the fastburn head it may be more accurately stated as "spark timing was lower than the 2.2L using the same cylinder head", for reasons indicated above.
Likewise and respectively, both engines will tolerate more spark advance with the G-Head.


Piston dish OD:
The piston dish diameter was changed between the 2.2L and the 2.5L.
This negatively affected the amount of squish when compared to the 2.2L using the same head.
Additionally, many subsequent aftermarket forged pistons, for both applications, have the squish band reduced.
A wider band with a slightly shallower dish may provide a compression bump with enough squish/quench to maintain the same level of spark advance, under the same boost conditions.

49392

Piston speed:
The elevated piston speeds on the 2.5L will increase the piston temperatures.
This will also increase, for obvious reasons, as boost is elevated and aggravates the engines sensitivity to knock.
As many are aware, this is also the reason why the later 2.4L turbo charged engines incorporated the use of oil squirters to counter act piston temperatures.

As reference, the values below indicate the approximate RPM's for a 2.0L, 2.2L, and 2.5L when the piston speeds are equalized.

2.5L - 6000RPM

2.2L - 6800RPM

2.0L - 7700RPM

To put things into perspective, the desire to run a 2.5L engine to 6500RPM is much like running a 2.0L to 8300RPM and may be something to consider during the next up-shift.

[wheming]

Ken - Maybe you have some insight into a question that's been bothering me for a while.

A G-Headed 2.5 is very difficult to tune. Too much timing and it knocks (seems to handle more timing than a FB head, though), too little timing and the EGT's soar; and performance drops dramatically.

What is it about the G-Head + 2.5l combination that makes it so difficult?

Interested in hearing more about this also.
Slug has flashed the CEL indicating knock since she has been fully rebuilt with JE forged slugs. Has indicated knock retard on OTC 4000 also. Still running 2.5l with G-head (MP mild port +1). Now running flashable though with 3 bar. Tried both +40's and now scaled for 95#/hr.

I'm getting concerned when I do get Mini back together I'll be in the same boat.

[Ondonti]

I think it is fair to say that the 782 head has some definite improvements that can be made to it, however there is more than 1 side to a combustion chamber. A combustion chamber is a volume. In our case we can change the ceiling and the floor. The ceiling is the head. The floor is the piston. Since I learned about quench, swirl, tumble...all that good stuff, the mismatch of the pistons to the heads for our engines has bothered me...a LOT. A large part of the reason the 782 head is "crappy" is because it really isn't being used to its full potential. There is a quench pad, but the piston crown does not match it, so it isn't used. The dish in the piston allows the charge to go off in a direction away from the spark plug. On top of that, the piston crown does nothing to support the continuation of swirl. It's just a "bucket". To me, if there was a proper piston made to work with the head design, I'm pretty confident that there would be gains in all kinds of areas.

Ken, on the filling of the long side of the intake port in the bowl, I seem to remember that there is a very slight offset on one side of the bowl. From reading what others have said over the years, and seeing the work of people that really know what they are doing with that type of port work, I was under the impression that that was part of what starts the swirl of the charge. The rest is directed by the chamber shape (and to some extent the valve and valve seat). I agree that filling the long side would certainly help, but it's important to note that it's not just an arbitrary filling.

BTW, it costs about the same to get the correctly made piston (hey vendors!) as it does improperly designed pistons. Who will be the first to market a proper piston? Nobody :( You can get this stuff done yourself but you shouldn't have to for a platform that still has some market.

I also bank ZERO $ into obsessing about pistons speeds because the baddest import engines start off with high piston speeds and they keep stroking them more and not looking back. They do what is necessary to prevent knock be it modified pistons, whatever. If you build the shortblock and design the pistons exactly the same and ignore pistons speeds or heat, that is your fault, not the engine's.

Now, spending all that time modifying a cylinder head and you plan on putting an off the shelf improperly designed piston in, again, your fault when things don't work.

Less spark advance is not a bad thing. A sign of a good turbo setup is needing less spark advance. Bad tuning practices carried over from older tech/poorly designed cylinder heads need to die. Just because its hard to tune something using backyard techniques does not mean that engine combo is junk. I don't like spending money so I would probably avoid the hard to tune cylinder heads so that backyard techniques will be good enough.

[roachjuice]

I've honestly just given up on the whole tuning these cars thing. I saw jack ----. Only thing I've got on my tune right now is scaled for injectors and map and no over boost. That's it. Stock timing. Stock everything else. Got soooooo tired running in and out the house flashing tunes and going out and beating on the car trying to see a change then cracking ring lands on multiple occasions. Done. Stock tune ftw. Afpr for fine tuning the afr. Done. Keep it simple.

[Force Fed Mopar]

I got decent results, 80mph in the 8th in a 3300 pound race weight fwd is decent power, but I spent A LOT of time burning cals, like 1 or 2 everyday. I also had forged Wiseco pistons so no ringland worries :) I have run up to 25 psi on mine, but after 17 psi it was definitely in the realm of diminishing returns. The 80mph was on around 20-22 psi though.

However, I never really could get it to not flash the knock light at those levels either, even with the knock threshold raised significantly. Now I know why :)

[5DIGITS]

BTW, it costs about the same to get the correctly made piston (hey vendors!) as it does improperly designed pistons.
Who will be the first to market a proper piston? Nobody :( You can get this stuff done yourself but you shouldn't have to for a platform that still has some market.
I also bank ZERO $ into obsessing about pistons speeds because the baddest import engines start off with high piston speeds and they keep stroking them more and not looking back.
They do what is necessary to prevent knock be it modified pistons, whatever.
If you build the shortblock and design the pistons exactly the same and ignore pistons speeds or heat, that is your fault, not the engine's.
Now, spending all that time modifying a cylinder head and you plan on putting an off the shelf improperly designed piston in, again, your fault when things don't work.
Less spark advance is not a bad thing. A sign of a good turbo setup is needing less spark advance.
Bad tuning practices carried over from older tech/poorly designed cylinder heads need to die.
Just because its hard to tune something using backyard techniques does not mean that engine combo is junk.
I don't like spending money so I would probably avoid the hard to tune cylinder heads so that backyard techniques will be good enough.

True - When effort is put towards the right hardware and its complimented with accurate tuning, everything will work together regardless if its new or old backyard technology or custom machined from top to bottom.

[Force Fed Mopar]

Would going to a flat top piston help anything?

[Force Fed Mopar]

To put things into perspective, the desire to run a 2.5L engine to 6500RPM is much like running a 2.0L to 8300RPM and may be something to consider during the next up-shift.

Just as a note, I always shifted mine before 6k, as it didn't really pull any more past that. Usually shifted around 5k-5500.

[wheming]

So are there any off the shelf forged pistons that are better than the rest? Which forged piston has this shelf dimension the broadest?
And this should be a bit less of an issue with the G head?

[5DIGITS]

So are there any off the shelf forged pistons that are better than the rest?
There are many high quality units on the market but consider the performance levels that are being attempted, to determine whether the investment is justified.


Which forged piston has this shelf dimension the broadest?
As previously mentioned, many manufacturers will support customer supplied dimensions.
This comes back to understanding the output expectation and how to best compliment the other components being used.
At that point, the decision can be made regarding forged components or cast and if the upgraded parts should be custom or off the shelf.


And this should be a bit less of an issue with the G head?
Yes.
The G-Head is a bit more forgiving when considering spark advance and elevated cylinder pressures.

[Force Fed Mopar]

Update: Got the Lebaron DD'ing again, and have been working on re-tuning nearly every day for a month now. I have come to the conclusion that my valvetrain is setting off the knock light in most cases. Most often I'd see it after lifting to shift in normal driving. It'll come on in the higher revs sometimes under power, but it's not really regular, and boost level doesn't seem to affect it much, only rpm and maybe engine temp. Even out of boost, just running it up to 3500ish in first gear while taking off easy from a light would set it off every time. This is all on completely stock timing and boost levels.

Revving the engine in neutral under the hood, I can hear the valves pretty clearly. Not sure why, as I am running 2.4 lifters w/ the hole in the top w/ a pretty good shim under them. They are used lifters, so I suppose they could just be worn out. The valve springs are also pretty old, they are from an '88 Daytona :D So they may be allowing some slap also? Cam is a stock turbo roller. Checked all brackets on the engine, everything seems to be tight. Engine does have a lot of vibration, shakes the hood and headlight doors a lot at idle (poly mounts), not so bad when revved up but still a little bit. Oil pressure is good.

So I've been raising the threshold a little at a time trying to eliminate the engine noise, but I'm worrying now that in doing so, it may not pick up on actual knock? How much louder is spark knock than a noisy valvetrain?

[shackwrrr]

Update: Got the Lebaron DD'ing again, and have been working on re-tuning nearly every day for a month now. I have come to the conclusion that my valvetrain is setting off the knock light in most cases. Most often I'd see it after lifting to shift in normal driving. It'll come on in the higher revs sometimes under power, but it's not really regular, and boost level doesn't seem to affect it much, only rpm and maybe engine temp. Even out of boost, just running it up to 3500ish in first gear while taking off easy from a light would set it off every time. This is all on completely stock timing and boost levels.

Revving the engine in neutral under the hood, I can hear the valves pretty clearly. Not sure why, as I am running 2.4 lifters w/ the hole in the top w/ a pretty good shim under them. They are used lifters, so I suppose they could just be worn out. The valve springs are also pretty old, they are from an '88 Daytona :D So they may be allowing some slap also? Cam is a stock turbo roller. Checked all brackets on the engine, everything seems to be tight. Engine does have a lot of vibration, shakes the hood and headlight doors a lot at idle (poly mounts), not so bad when revved up but still a little bit. Oil pressure is good.

So I've been raising the threshold a little at a time trying to eliminate the engine noise, but I'm worrying now that in doing so, it may not pick up on actual knock? How much louder is spark knock than a noisy valvetrain?

Hey, I have the other half of my set of 26995 springs. my van hasn't even hinted at setting the knock light since Ive installed them. I have just the springs all you need for retainers are stock gm 3100/3400 retainers.

I bought the springs for 180ish I would sell the other half for 95 shipped if you are interested. I was able to do them on the van with an air fitting and an on car spring compressor.

[Force Fed Mopar]

I actually have a set of those also, just need to get retainers. I think that will be my next real mod on the car. Summit sells a 8mm beehive retainer for Jeep 4.0's that I think should have the right keeper angle for the stock keepers, so I'm gonna order one and see. If so, I'll order a set and install. If not, guess I'll rock some GM retainers like everyone else :)

[zin]

Summit sells a 8mm beehive retainer for Jeep 4.0's that I think should have the right keeper angle for the stock keepers, so I'm gonna order one and see.

I'm very keen on seeing if they do mate up properly, not knowing is the main reason I haven't gone this route... I just don't like the idea of the keepers and retainers not having matching angles... I know the other way works, but I get nervous in regards to the possibility of valves dropping, I've seen what can happen, and I don't what to be "that guy".

Mike

[Force Fed Mopar]

I posted this in another but I'll update it here also. I finally got brave enough to just set the knock threshold to 5v so it wouldn't come on and started tweaking up the timing. So far so good and it feels stronger then it ever has at 15 and 18 psi. Also running it slightly rich seems to make better power also, 10.8-11.0. Could be that my sensor isn't reading right anymore either, it's a few years old now.

[wheming]

I posted this in another but I'll update it here also. I finally got brave enough to just set the knock threshold to 5v so it wouldn't come on and started tweaking up the timing. So far so good and it feels stronger then it ever has at 15 and 18 psi. Also running it slightly rich seems to make better power also, 10.8-11.0. Could be that my sensor isn't reading right anymore either, it's a few years old now.

How are you monitoring knock then, just audibly? Or do you have the det can?

[Force Fed Mopar]

Just listening by ear, no det can yet. I know, dangerous...

[wheming]

I'm not judging...
I ask because I've experienced the similar occurence with Slug after rebuild (which included forged pistons) and using a turbonator cal with the CEL on knock retard.

Now, with MeanMini's rebuild it is observed also at low boost levels.
I'm inclined to believe it is noise or a sensitivity issue, as others theorize. I think it would be nice to have this feature and have it be a true indicator. I'm sure I'm not the first to wonder if we can use a better knock sensor from a different application?

Having at least a det can setup we could hear with our ears, but I'd like the computer to be able to hear "real" knock and then respond with retard and CEL flash.

While it may be agreed to not be an optimum way to tune, we do need to be able to recognize/observe/measure real knock to make sure we maintain a safety margin when trying to optimize a tune.

[ShelGame]

Any knock sensor is really just a microphone. As such, it picks up all noise.

In our system, the noise is used to charge a capacitor. The ecu then reads the voltage stored in the cap. This voltage is then compared to the knock threshold and rpm to determine if its knock, or just normal engine noise.

When you make major changes to the engine, it may naturally make more noise. You will then need to retune the knock threshold vs. rpm table to tell the ecu what voltage levels are OK and what is generated by knock. That's where the det can comes in handy.

If you modify the engine (even by just raising the boost) the stock knock threshold will no longer be valid.

Getting a 'better' knock sensor won't automatically fix everything. You still have to tell the difference between OK noise and knock.

[5DIGITS]

I'm not judging...
I ask because I've experienced the similar occurence with Slug after rebuild (which included forged pistons) and using a turbonator cal with the CEL on knock retard.

Now, with MeanMini's rebuild it is observed also at low boost levels.
I'm inclined to believe it is noise or a sensitivity issue, as others theorize. I think it would be nice to have this feature and have it be a true indicator. I'm sure I'm not the first to wonder if we can use a better knock sensor from a different application?

Having at least a det can setup we could hear with our ears, but I'd like the computer to be able to hear "real" knock and then respond with retard and CEL flash.

While it may be agreed to not be an optimum way to tune, we do need to be able to recognize/observe/measure real knock to make sure we maintain a safety margin when trying to optimize a tune.

What would help these cars is a knock sensor the utilizes 'sensor ground' rather than vehicle ground, to aid in noise isolation.
With the current single wire sensor, injector coil inductive collapse and alternator noise can be induced into the signal based on 'chassis' ground conditions.
If the production sensor is used, discard the passenger side clip-on ground strap and drill the opposing sides of the mount for bolt on wire eyelets.
Furthermore, add an eyelet equipped strap from the injector harness ground to the frame side of the passenger side mount.
This will improve the knock sensor accuracy especially if the sheet metal bulk head ground bolt is stripped or the passenger side mount strap has deteriorated over time.

[zin]

Ken, am I understanding you, in that you're suggesting a better ground to lower the induced voltage in the single wire of the knock sensor?

I'm wondering a couple of things, first, that some folks frustration with knock not being well controlled could be related to 30year old capacitors not holding tolerance and an ECU that still expect such. Which begs the question, can that CAP be replaced?, or is there another "work-around" that would be better?

Second, if my understanding is correct, the sensor we use generates it's own voltage via piezoelectric effect, so adding a "clean ground" between the intake and the sensor wouldn't dramatically help things, but would adding a grounded sheath around that single wire for a distance have benefits worth the investment in time?

Mike

PS Rob, thanks for the explanation of the knock circuit, it helped make things "click" in me brain!:thumb:

[cordes]

Would installation of a multi-wire modern knock sensor be possible with stock electronics?

[ShelGame]

What would help these cars is a knock sensor the utilizes 'sensor ground' rather than vehicle ground, to aid in noise isolation.
With the current single wire sensor, injector coil inductive collapse and alternator noise can be induced into the signal based on 'chassis' ground conditions.
If the production sensor is used, discard the passenger side clip-on ground strap and drill the opposing sides of the mount for bolt on wire eyelets.
Furthermore, add an eyelet equipped strap from the injector harness ground to the frame side of the passenger side mount.
This will improve the knock sensor accuracy especially if the sheet metal bulk head ground bolt is stripped or the passenger side mount strap has deteriorated over time.

Don't know why I didn't think of that myself. Makes me wonder now how many guys that seem to get the knock sensor going off based on 'valvetrain' or 'piston' noise actually just have a bad ground or 2. I can imagine that if your ground wire to the manifold/fuel rail is working well, but another ground to the engine is not, that you could indeed get some bad flyback voltage on the ground wire closest to the knock sensor. The spark plugs / coil would be the prime example as they are grounded thru the block.

- - - Updated - - -


Would installation of a multi-wire modern knock sensor be possible with stock electronics?

We'd have to find a 2-wire knock sensor with the same output characteristics as ours. But, if there is one, I imagine it could be an improvement. At least in reliability.


EDIT:
Perhaps a '95 Neon knock sensor would fit the bill?

http://www.ebay.com/itm/Ignition-Knock-Detonation-Sensor-Senso-AIRTEX-5S2181-/281318654415?fits=Year%3A1995%7CMake%3ADodge%7CMod el%3ANeon&hash=item417fe601cf&vxp=mtr

I think it must have similar (if not the same) output characteristics - the '95 FCC is basically an SBECII, specialized for 4-cylinder only duty.

[Force Fed Mopar]

What would help these cars is a knock sensor the utilizes 'sensor ground' rather than vehicle ground, to aid in noise isolation.
With the current single wire sensor, injector coil inductive collapse and alternator noise can be induced into the signal based on 'chassis' ground conditions.
If the production sensor is used, discard the passenger side clip-on ground strap and drill the opposing sides of the mount for bolt on wire eyelets.
Furthermore, add an eyelet equipped strap from the injector harness ground to the frame side of the passenger side mount.
This will improve the knock sensor accuracy especially if the sheet metal bulk head ground bolt is stripped or the passenger side mount strap has deteriorated over time.


Don't know why I didn't think of that myself. Makes me wonder now how many guys that seem to get the knock sensor going off based on 'valvetrain' or 'piston' noise actually just have a bad ground or 2. I can imagine that if your ground wire to the manifold/fuel rail is working well, but another ground to the engine is not, that you could indeed get some bad flyback voltage on the ground wire closest to the knock sensor. The spark plugs / coil would be the prime example as they are grounded thru the block.


Never thought of this myself either. I think I have a ground from the intake to the firewall, not sure about the motor mount. If it does it's just the clip on type. I'll have to add grounds as mentioned and see how it does.

[cordes]

Don't know why I didn't think of that myself. Makes me wonder now how many guys that seem to get the knock sensor going off based on 'valvetrain' or 'piston' noise actually just have a bad ground or 2. I can imagine that if your ground wire to the manifold/fuel rail is working well, but another ground to the engine is not, that you could indeed get some bad flyback voltage on the ground wire closest to the knock sensor. The spark plugs / coil would be the prime example as they are grounded thru the block.

- - - Updated - - -



We'd have to find a 2-wire knock sensor with the same output characteristics as ours. But, if there is one, I imagine it could be an improvement. At least in reliability.


EDIT:
Perhaps a '95 Neon knock sensor would fit the bill?

http://www.ebay.com/itm/Ignition-Knock-Detonation-Sensor-Senso-AIRTEX-5S2181-/281318654415?fits=Year%3A1995%7CMake%3ADodge%7CMod el%3ANeon&hash=item417fe601cf&vxp=mtr

I think it must have similar (if not the same) output characteristics - the '95 FCC is basically an SBECII, specialized for 4-cylinder only duty.

That sensor could be the ticket. I seem to recall Bucar mentioning that the frequency tuning is based off of bore dia. That would bode really well for us in that aspect. That said, I would still be surprised if it only took a little extra wiring to use it.

[ShelGame]

That sensor could be the ticket. I seem to recall Bucar mentioning that the frequency tuning is based off of bore dia. That would bode really well for us in that aspect. That said, I would still be surprised if it only took a little extra wiring to use it.

That's a good point, the Neon is the same bore diameter and spacing.

Another eBay search tells me that they used the same sensor up until 2003 (which is when they made the switch to NGC electronics, coincidentally).

Since the knock sensor it's basically a microphone, it doesn't really have polarity. You just need to take 1 side to the sensor input, and the other to the ECU sensor ground. The MAP sensor is in the same stretch of harness, so there should be a good place to splice it in nearby.

Oh, and we'll need to find a mating connector for the sensor itself.

Since I'm building the harness right now, I think I'll try this on my Omni. It's the BB rolling testbed afterall.

[Aries_Turbo]

Buyer's Guide: AIRTEX / WELLS 5S2181 Knock (Detonation) Sensor
CHRYSLER INTREPID 2001
CHRYSLER NEON (2000 - 2002)
CHRYSLER PT CRUISER (2001 - 2002)
CHRYSLER SEBRING (1995 - 2002)
CHRYSLER VOYAGER (2000 - 2002)
DODGE AVENGER (1995 - 1999)
DODGE CARAVAN (1996 - 2002)
DODGE GRAND CARAVAN (1996 - 1997)
DODGE INTREPID 2001
DODGE NEON (1995 - 2002)
DODGE STRATUS (2001 - 2002)
EAGLE TALON (1995 - 1998)
MITSUBISHI ECLIPSE (1995 - 1999)
PLYMOUTH GRAND VOYAGER (1996 - 1997)
PLYMOUTH NEON (1995 - 2001)
PLYMOUTH VOYAGER (1996 - 2000)

this is what rockauto has for this sensor. i hope it isnt manufactured that generally..... unless all those vehicles have the same size bore. i mean i know the 4 bangers for all those vehicles have the same bore more or less but the intrepid doesnt have a 4 cyl option as far as i know. its gotta be for 2.7L vehicles as they have a 3.4" bore from what i can find with a quick search.


CHRYSLER PT CRUISER (2001 - 2002)
CHRYSLER SEBRING (1995 - 2001)
CHRYSLER VOYAGER (2001 - 2002)
DODGE AVENGER (1995 - 2000)
DODGE CARAVAN (1997 - 2002)
DODGE NEON (1995 - 2002)
DODGE STRATUS (2001 - 2002)
EAGLE TALON (1995 - 1998)
MITSUBISHI ECLIPSE (1995 - 1999)
PLYMOUTH GRAND VOYAGER 1997
PLYMOUTH NEON (1995 - 2001)
PLYMOUTH VOYAGER (1997 - 2000)

this is what the BECK/ARNLEY Part # 1581245 has for vehicles which makes sense as all of those vehicles could be had with a 2.0L or 2.4L.

that connector pic looks alot like the later model plastic solenoid connectors. i think i may have one of these sensors on a 2.0L neon motor in my garage.

Brian

[Aries_Turbo]

as far as aftermarket controllers, risen and i were working on an arduino based knock control board (TI DSP chip, later wideband sensor, crank angle listening window, per cyl knock values, per cyl/per rpm based noise curve, and a super simple to program and datalog hyperterminal interface) but we got so busy with life.

my neon is still wired with an additional knock sensor and crank/cam sensor taps and 5v/gnd taps to the ecu to drive the board. i was testing in the testing phase but i really needed some more time to install a det can (to audibly listen for knock) and to make sure the car wasnt knocking at all for some baseline data. and then make a hot air intake, put crap gas in it and make it actually knock so i could get some valid test data.

ill see if i can get ahold of him and see if we can revive it. i suck at coding so id need help from someone who doesnt.

Brian

[5DIGITS]

I'm starting to wonder how the tables and related cal constants are being manipulated.
It may be helpful to understand the true issue(s), whether it's a calibration problem or a knock light code problem so the effort avoids re-inventing the mouse trap.

For example, the following table has been reliably used on a T-II with a 'G' head, two-piece intake (with support bracket installed - it matters!!) and slider cam at 22 PSI.

RPM VOLTS
992 .350
1504 .630
2016 1.590
2528 3.310
3040 3.860
5984 4.000

[zin]

....(with support bracket installed - it matters!!)...

This sounds like the beginning of an interesting story(s)... care to share?:)

Mike

[Reaper1]

Probably has something to do with vibration attenuation and how it affects resonance at certain rpm that can make the knock sensor send a false signal. Just guessing...

[zin]

Don't spoil the story!:p

Mike

[5DIGITS]

Probably has something to do with vibration attenuation/amplification and how it affects resonance at certain rpm that can make the knock sensor send a false signal. Just guessing...

Well said - yes.
A reference visual is a pool diving board and the effect of attaching a bracket from the side of the pool to the end of the board.

[zin]

Awe come on, I'm looking for the, "we pulled our hair out for weeks trying to figure out this gremlin" story!

Mike

[Reaper1]

So was it simply the structural design of the 1-piece that made the bracket obsolete? How should people be thinking about this while making custom intakes that utilize the 2-piece lower runners?

Oh...and the story! ;) (I hope we don't bother you like 5 year olds for a bedtime story, but it truly is fascinating to hear about the behind the scenes development behind this stuff...especially since it pretty well set how computer controls work)

[5DIGITS]

So was it simply the structural design of the 1-piece that made the bracket obsolete? How should people be thinking about this while making custom intakes that utilize the 2-piece lower runners?
Oh...and the story! ;) (I hope we don't bother you like 5 year olds for a bedtime story, but it truly is fascinating to hear about the behind the scenes development behind this stuff...especially since it pretty well set how computer controls work)

In my opinion, the one piece should have also had a support bracket.
Even the old aluminum intake 3.3 and 3.8 V6 engines had them and ironically on the added TB hung mass end of the intake.
It's simply too much mass to hang off the head unsupported.

Thankfully the exhaust side received a bracket due to the turbo mass and added tugging of exhaust system.

[Force Fed Mopar]

So those support brackets eliminate vibrations that can affect the knock sensor? I don't remember if I have either one on mine.

[Ondonti]

as far as aftermarket controllers, risen and i were working on an arduino based knock control board (TI DSP chip, later wideband sensor, crank angle listening window, per cyl knock values, per cyl/per rpm based noise curve, and a super simple to program and datalog hyperterminal interface) but we got so busy with life.

my neon is still wired with an additional knock sensor and crank/cam sensor taps and 5v/gnd taps to the ecu to drive the board. i was testing in the testing phase but i really needed some more time to install a det can (to audibly listen for knock) and to make sure the car wasnt knocking at all for some baseline data. and then make a hot air intake, put crap gas in it and make it actually knock so i could get some valid test data.

ill see if i can get ahold of him and see if we can revive it. i suck at coding so id need help from someone who doesnt.

Brian
I would say I have been waiting but I have done nothing but be busy :(

So those support brackets eliminate vibrations that can affect the knock sensor? I don't remember if I have either one on mine.

Thinking of all the brackets I have deleted makes me wonder about interpreting knock voltage. How about other vibrations that people even complain about feeling through their steering wheels?

[acannell]

Heres the two things that stick out to me regarding knock sensors for our engines:

#1 - Shadow has apparently been using the stock sensor with success at very high power levels. Right there is a show stopper as far as developing any new way of doing things, as far as I can tell. Or at least it raises the question "Why is anything else required?"

#2 - If someone is going to develop and/or modify things to be better, the place to start is characterizing the knock signal. You cant figure out how to detect knock or improve knock detection without knowing exactly what signal you are trying to detect. Otherwise how do you know if you are successful or whether your algorithm/electronics package is correct? For the engineers here, just pretend you are doing this at work. Your boss comes in and says "Okay Bill, I'm putting you in charge of the new 2.2/2.5 knock detection project." "Okay Boss. So what does this knock signal look like we're trying to detect?" "I dunno just tweak whatever already exists and make arguments about why it should work." "Thanks Boss."

[5DIGITS]

Heres the two things that stick out to me regarding knock sensors for our engines:

#1 - Shadow has apparently been using the stock sensor with success at very high power levels. Right there is a show stopper as far as developing any new way of doing things, as far as I can tell. Or at least it raises the question "Why is anything else required?"

#2 - If someone is going to develop and/or modify things to be better, the place to start is characterizing the knock signal. You cant figure out how to detect knock or improve knock detection without knowing exactly what signal you are trying to detect. Otherwise how do you know if you are successful or whether your algorithm/electronics package is correct? For the engineers here, just pretend you are doing this at work. Your boss comes in and says "Okay Bill, I'm putting you in charge of the new 2.2/2.5 knock detection project." "Okay Boss. So what does this knock signal look like we're trying to detect?" "I dunno just tweak whatever already exists and make arguments about why it should work." "Thanks Boss."

The electrical issue with erratic KS readings are poor grounds while considering the sensor being used on the 2.2/2.5L.
The mechanical issue with erratic KS readings on the 2.2/2.5L configuration is the use of tired or out of spec. hardware components.
These can usually be monitored, isolated and/or tested under lighter load conditions while monitoring the knock parameters/signals.

For the determined, Kistler cylinder probes or Kistler spark plugs provide the insight necessary to differentiate whats being detected.

http://www.turbo-mopar.com/forums/attachment.php?attachmentid=54276&stc=1

[Ondonti]

Heres the two things that stick out to me regarding knock sensors for our engines:

#1 - Shadow has apparently been using the stock sensor with success at very high power levels. Right there is a show stopper as far as developing any new way of doing things, as far as I can tell. Or at least it raises the question "Why is anything else required?"

#2 - If someone is going to develop and/or modify things to be better, the place to start is characterizing the knock signal. You cant figure out how to detect knock or improve knock detection without knowing exactly what signal you are trying to detect. Otherwise how do you know if you are successful or whether your algorithm/electronics package is correct? For the engineers here, just pretend you are doing this at work. Your boss comes in and says "Okay Bill, I'm putting you in charge of the new 2.2/2.5 knock detection project." "Okay Boss. So what does this knock signal look like we're trying to detect?" "I dunno just tweak whatever already exists and make arguments about why it should work." "Thanks Boss."

Shadow is running enough octane that HP would probably fall off the earth before it started knocking. If he wanted to optimize his pump gas setup and knock was happening before power peaked, then he would get some cool gains with cylinder specific knock detection.

[acannell]

Shadow is running enough octane that HP would probably fall off the earth before it started knocking. If he wanted to optimize his pump gas setup and knock was happening before power peaked, then he would get some cool gains with cylinder specific knock detection.


Okay so then that explains that (unless Shadow indicates otherwise).

So I think we can agree there wouldnt be a problem with designing a system that could detect knock at power levels that arent destructive, because we can actually force knock to happen at those levels, measure the signals, and design based 100% on testing.

The problem is with higher power knock, where we cant measure the signals, because we'll be breaking parts (unless someone wants to take one for the team lol)

But, I think if we make one assumption, that knock at 500hp will be at least as high in amplitude as knock at 150hp, we can still design a system where we have a high confidence level.

First, force knock to occur at low power levels, say 10psi, and with forged pistons just as an added measure (and since our new system would likely be used with forged).

Record the knock sensor output with a digital scope, including the background noise level.

Then, raise the power level to 500hp (or whatever), with proper AFR.

Record the background noise level.

Then design the system to detect the low-power knock signal, but with the high power background noise. If thats possible, given what the data shows (i.e. high power background noise not burying low power knock signal), then I think thats a good start.

And of course, measuring knock at the low power level is probably going to require a few different scenarios, perhaps varying timing, etc.. to account for things which may move or alter the knock signal.

[wheming]

I'd like to see exactly how this 2pc intake support bracket looks, and to what bosses it mounts.
Can this still be accomplished with a TU header?

I'm very happy to see the suggestion of both the main electrical & mechanical reasons for erratic KS readings. I had intended to go through and make better grounding wires in some areas, but did not know it may specifically fix something i may be experiencing. I just knew these grounds weren't great by now given the age.
So thank you very much for those tips! :beer:

[5DIGITS]

I'd like to see exactly how this 2pc intake support bracket looks, and to what bosses it mounts.
Can this still be accomplished with a TU header?

I'm very happy to see the suggestion of both the main electrical & mechanical reasons for erratic KS readings. I had intended to go through and make better grounding wires in some areas, but did not know it may specifically fix something i may be experiencing. I just knew these grounds weren't great by now given the age.
So thank you very much for those tips! :beer:


http://www.turbo-mopar.com/forums/attachment.php?attachmentid=54281&stc=1

Bolts from the underside of the TB neck to the front upper boss of the cylinder head.

[5DIGITS]

This was posted further upstream in the thread and useful as we go full circle.

__________________________________________________


As indicated within the thread, this area of calibration does not typically require excessive effort and recalibrating the knock sensor should not be considered an approach to mask mechanical issues or support increased spark advance.
But for those who are interested in gaining additional information, the following steps can help identify what the levels are and where the peak values are realized.

The production knock sensor calibration values were set to avoid any and all audible knock, for customer satisfaction purposes.
This also includes an effort to preserve the head gasket, avoid dealership repair downtime, and the resulting warranty costs.
The result has the spark reduction process somewhat hyperactive and over-sensitive even in the stock configuration.
Considering that many of the vehicles on the forum are modified, the challenge becomes understanding how the modifications have affected the mechanical and combustion noise levels, relative to the knock sensor.
This is where a CAS (Combustion Analysis System) would be very useful but without it there are a couple ways to understand the back ground/operational noise levels, specific to your vehicle.

Considerations:
The engine should be in good mechanical condition, for obvious reasons.
Please make sure all engine and sensor grounds are intact and the controller is free of any faults that would alter the results.
High output ignition systems can impact the sensor noise levels - consider testing with and without.
Confirm that the injectors metal body do not contact/touch any portion of the intake manifold.
When this occurs, the injector will transfer its mechanical noise into the intake.

Getting started...
Considering that combustion noise will vary as a function of load/MAP and the mechanical noise is best identified with minimal cylinder pressure, we can attempt to isolate them and determine a general baseline for each.
The following steps are best completed while monitoring/recording engine RPM, MAP, and knock sensor voltage, via any safe means possible.
Again, this is far from combustion analysis but it can provide added insight, for those who are interested.

Mechanical Evaluation :



Retard spark advance via the distributor or in cal (for DIS) by 4-6 degrees throughout all operating conditions
(Depending how much spark advance is being used, this reduces the opportunity for detonation while testing)
With a warm engine, start at the lowest possible throttle angle/load, record the knock sensor voltage while slowly increasing the engine RPM from 1000 to the safest peak RPM
Decelerate the engine slowly, to avoid rapid low-load engine unwind
Let the engine idle for several minutes to de-aerate the oil and minimize any resulting valve-train/piston noise
Repeat the data collection process and confirm consistency with each previous run
These steps should not exceed ten (10) inches of vacuum, to remain at minimum cylinder pressures
At this point, a 'general' mechanical baseline has been identified, as seen by the knock sensor
If there's interest, a test can also be done between 2500-3500RPM while dithering the throttle
This induces varying combustion chamber pressure levels which excites wrist-pin and piston slap noise


The mechanical traces should be fairly consistent producing essentially a single knock sensor voltage curve, for the narrow MAP range used.


The next steps duplicate the previous process but introduces load.
The load intervals should be selected based on what you're willing to repeat up to elevated boost levels.
(For example: 2.5, 5, 10, 15psi, increments etc... )
This typically requires dragging the brakes under elevated torque conditions - USE CAUTION !

Combustion Evaluation :



Retard spark advance via the distributor or in cal (for DIS) by 4-6 degrees throughout all operating conditions
(Depending how much spark advance is being used, this reduces the opportunity for detonation while testing)
With a warm engine, start at atmospheric load, record the knock sensor voltage while slowly increasing the engine RPM from 1000 to the safest peak RPM
Let the engine idle for several minutes to de-aerate the oil and minimize any resulting valve-train/piston noise
Repeat the data collection process at the selected load to confirm run to run consistency
With repeatable results, increase the load to your next chosen level and repeat the previous steps
Considering the testing process, repeat the above steps only to a peak boost level that your comfortable with
At this point, the impact of increased cylinder pressure is identified as the growth of knock sensor voltage that exceeds the previously recorded mechanical results



The load based knock sensor curves will elevate as MAP increases but they don't always increase at the same rate between the tested boost levels.
This is the reason for collecting multiple load results and this should be considered when determining the knock table voltages for boost levels beyond the test levels.

I hope this helps and enjoy.

[wheming]

So that just is supported back to one of the bolts on the side of the head?
I'll have to see how best to adapt a braket with the Lengel upper plenum.
Thanks for the pic!

[wheming]

I'm starting to wonder how the tables and related cal constants are being manipulated.
It may be helpful to understand the true issue(s), whether it's a calibration problem or a knock light code problem so the effort avoids re-inventing the mouse trap.

For example, the following table has been reliably used on a T-II with a 'G' head, two-piece intake (with support bracket installed - it matters!!) and slider cam at 22 PSI.

RPM VOLTS
992 .350
1504 .630
2016 1.590
2528 3.310
3040 3.860
5984 4.000

Do you have any data for a 2.5 turbo running similar components and boost for comparison purposes?
Or would you be inclined to think these settings would add safety margin if the only difference was 2.5 vs 2.2?

[5DIGITS]

Do you have any data for a 2.5 turbo running similar components and boost for comparison purposes?
Or would you be inclined to think these settings would add safety margin if the only difference was 2.5 vs 2.2?

The 2.5 peak combustion efficiency occurs at lower RPM and the delta knock table will need to reflect that.
Send me a PM with what your running for a cam, intake, turbo, head, compression, etc...
If I have a closely resembling cal, I'll pull the table for you.

[Force Fed Mopar]

I'm starting to wonder how the tables and related cal constants are being manipulated.
It may be helpful to understand the true issue(s), whether it's a calibration problem or a knock light code problem so the effort avoids re-inventing the mouse trap.

For example, the following table has been reliably used on a T-II with a 'G' head, two-piece intake (with support bracket installed - it matters!!) and slider cam at 22 PSI.

RPM VOLTS
992 .350
1504 .630
2016 1.590
2528 3.310
3040 3.860
5984 4.000

I put those values into a cal on MP Tune to get a visual of the curve, looks like the noise ramps up quickly until 3k. Not sure what turbo you had but I know the stock turbo hits full song by that point.

[5DIGITS]

I put those values into a cal on MP Tune to get a visual of the curve, looks like the noise ramps up quickly until 3k. Not sure what turbo you had but I know the stock turbo hits full song by that point.

Agreed and good point.
When the knock signal is free of outlying issues, the curve typically mimics the efficiency curve of the engine for obvious reasons.
The turbo was a T3/T4 hybrid with a modified Turbonetics/Chrysler turbine housing.