How would ported head affect ignition needs?

[tryingbe]

Since I put in the 2.2L with a ported head (bought a car came the engine, I assume the head work is done by forward motion over 10 years ago) couple months ago, car is knocking slightly under boost around 7psi, using AZ winter blend 91 oct gas. The knock is verified with the OTC 4000E scanner, I can see the knock voltage goes up and ignition timing being pulled. I'm using turbonator LM calibration, using stock 87 TII ignition timing for ignition all tables, 10psi, 11.5 a/f. Since I am working on my other car, I haven't done much other test, other than driving it easy.

Yesterday, I mixed in 4 gal of E85 and rest with 91 octane gas, kept the same tune, while WOT a/f is up from 11.5 to 12.5, no knocks! I've driven 130 miles so far, not a single knock. So, I'm going to pull even more timing off the ignition table so I can have a good 91 octane calibration.

How would a ported head affect ignition timing needs? I know G head need more ignition timing while Swirl head doesn't. Is it possible a ported head would need less timing than a stock Swirl head?

Here's the head in question.


This is the only decent picture I have of the porting done. Before the head was cleaned up and installed.



Thanks for any and all advises.

[mopar-tech]

1) That chamber already looks like it has had some work done to it to desensitize it for pressure spike and increase flow.

2) Are you getting knock in a certain rpm band? does it go away at higher boost level? Knock at 7 psi but not 10 would be very unusual.

3) Cranking compression?

Gary

[Vigo]

I doubt that the issue here has anything to do with the chamber work on that head. Is it pulling timing pretty evenly across all cylinders?

[Force Fed Mopar]

My stock swirl is pretty sensitive between 2700ish-3500, right when it spools. Which with the stock turbo and a 2.5, it'll spool hard, like 20psi at 3k. Below 14psi it seems much more tolerant though.

[puppet]

How would a ported head affect ignition timing needs?

A lot of assumptions are going to be made here mostly 'cause the head is on the block. I'm guessing that you don't have any measurements of the combustion chambers total volume ... and frankly, how relevant that might be (to ignition timing) considering you've changed fuel during the comparison. Is one cylinder knocking or all of them?

In general, chamber size will dictate time of burn. However, a more efficient chamber may allow for a faster burn overall. Faster burning fuels (lower octane) will obviously want reduced timing. Your E85 mix is obviously burning faster and maybe cooler. (aluminum heads will like that) Is the fueling matched to the heads flow capability? Preferably, on a dyno, you could find the total ignition timing sweet spot for max power/torque. Your introducing variables right now that will have a direct impact on where the spark should be.

[OmniLuvr]

what else has changed on the build besides the head, was the bmf intake on there before or is that a new item too? cam? cam timing? maybe there is a lot more flow happening with the bmf and ported head?

Your E85 mix is obviously burning faster

^slower and cooler, but results vary because its more blended, nice to kind of give you an idea, but not suggested

[Ondonti]

Well first of all I can't imagine you guys are pulling enough timing at that RPM when you are running 4x stock boost a peak cylinder pressure rpm (peak torque). Ignoring changes made to the combustion chamber, anything you do to decrease backpressure or change "in" flow will change your timing requirements. Less backpressure always means less timing required.

[puppet]

^slower and cooler, but results vary because its more blended, nice to kind of give you an idea, but not suggested

I disagree here. At a 1:1 air fuel ratio, gasoline burns at 26cm/sec and ethanol burns at 41cm/sec.

[OmniLuvr]

It burns at a much cooler temperature and slower than gasoline. Consequently, this slower burn rate, around 18 to 22 percent slower depending on the conditions

I just googled it very quickly, and pulled that ^ from hot rod magazine (not very scientific sorry, and have read other contradicting facts, im going off what I have experienced also)... the slower burn and cooler temp is what gives ethanol its higher octane rating at the proper afr's...

burning faster, or too fast is what causes the pressure wave colliding with itself we call detonation... so if knock went away when adding e85 to his fuel, then he added more octane, there for a "slower" burn... lower octane = quicker burn...

I don't wanna fill this thread with e85 crap (but id like to see more threads on the subject), so im hoping we will get answers on everything that was changed from previous "engine" to now, including tune. moparules was also "possibly" having some knock problems after installing the bmf intake (not sure, he may have found other problems too) but this could be exciting news to me do to higher flowing characteristics of the new intake...

[puppet]

OmniLuvr, I'll agree not to turn this into an E85 thread but as it relates to what Harry is doing (mix and comparison to pure petrol as it relates to timing with a ported head) is comparing apples and oranges and doesn't help in understanding the issue he's experiencing. E85 tuning strategies on forums are all over the place as are the why(s) you can do xyz with it over plain petrol tunes. I'll submit that some engines want more ign advance but can't get there with pure petrol. The charge cooling changes that. You see some FI alky tunes running rich in the mid rpm range w/adv timing (to help spool times) and leaning out the AFR in higher rpms while reducing timing for best power. The burn rates vary with the in cylinder volume of fuel present in these cases.

I'll just throw this out there FWIW and as it relates to the topic at hand. Alcohol(s) cools the charge temp. It stands to reason that you can run more ign advance if knock was heat related. Alky injection kits prove this. Do those kits add octane or cool the charge so far (as it relates to knock) that a guy can increase timing? If providing more advance enables the engine to make better power then that's great. It also may not ... but with alky(s) present, you can still advance timing because knock is being suppressed, thinking (lacking dyno data) that you're still making power. This scenario doesn't speak to how the ported head affected the timing though. Make sense?

Harry needs to pick a blend and tune for that. The ign timing he ends up with will be relative.

[tryingbe]

1) That chamber already looks like it has had some work done to it to desensitize it for pressure spike and increase flow.

2) Are you getting knock in a certain rpm band? does it go away at higher boost level? Knock at 7 psi but not 10 would be very unusual.

3) Cranking compression?

Gary

I can only answer #3 for now.

170, 167, 160, 162

I'm also not using a stock intake manifold, using Asa's BMF sheet metal intake manifold with the knock sensor block welded between #2 and #3 runner.

[GLHS60]

Probably should re phrase your question Harry:

"How would a BMF intake with a remounted knock sensor affect ignition needs along with a slightly deshrouded swirl head"

and higher than normal cranking compression, Good catch Gary.

Good discussion !!

Thanks
Randy

[mopar-tech]

I can only answer #3 for now.

170, 167, 160, 162

That is a lot of cranking compression, not sure I recall one with more. 110-125 is fairly normal on stock TII engines.

[shackwrrr]

What cam and did you degree it in? That high of cranking compression sounds like a possible over advanced camshaft.

[shadow88]

I noticed increased knock sensitivity with my ported and deshrouded head as well, over the previous ported head with untouched combustion chambers.

I'm betting that it had to do with partial removal of the quench area.

[Vigo]

Even a fresh rebuilt TBI engine doesn't have cranking compression that high. I also suspect an over-advanced camshaft at this point.

[cdavis]

That is a lot of cranking compression, not sure I recall one with more. 110-125 is fairly normal on stock TII engines.

Yeah, I agree with Gary. I just did a comp test on mine this weekend. It's freshly rebuilt, but with slightly lower comp ratio. It was 125 on all 4. This is with a tbi cam.

[OmniLuvr]

This scenario doesn't speak to how the ported head affected the timing though. Make sense

so what your saying is that the new combo is making so much more heat that it used the alcohol to cool the charge temps down enough that there wasn't a knock problem anymore?

what im trying to say is that the new combo could be flowing so much more at lower rpm's that he needs less timing at the same boost level because the resulting combustion process is greater than it was at the previous boost level, the e85 masked the knock problem because of increased "octane" rating.

so alcohol burns "faster" outside of an engine, but inside the intake port and combustion chamber, the cooling effect is so great that it increases "octane" which will "slow" the burn time down.

I was hoping I was going to get more answers from my original questions, 1 was the bmf intake is a new addition! wooo! I was also wondering about cam timing, or if the cam had been changed. also, what has been said before about the quench area being removed is a big part of it! why I don't like swirl heads personally.

[puppet]

OmniLuvr ... at this point you should probably check out some sites that actually deal with tuning on high alky fuels. What I'm saying is that e85 is a high octane fuel that cools the charge better than race gas (great knock suppression) but burns quicker.

I've read on other forums, posts by good engine builders, that don't support the "on paper" quench characteristics to the point of not being too concerned about it either way in their builds. They tend to optimize the chambers for better, more complete, burn. Their focus is power. Piston quench is down the list a ways. So, I don't know how much of a real issue that would be in this case.

[OmniLuvr]

I've read on other forums, posts by good engine builders, that don't support the "on paper" quench characteristics to the point of not being too concerned about it either way in their builds. They tend to optimize the chambers for better, more complete, burn. Their focus is power. Piston quench is down the list a ways. So, I don't know how much of a real issue that would be in this case

the only problem with this is comparing our cylinder head design to other engine designs, that's apples to oranges other than the fact they are both fruits. the valve placement and angle, the size of the pistons and combustion chamber in realation to that all have an effect. I am no way an "engine builder" but have built (a reasonable amount) and tuned a few engines on e85. ive also been in plenty of cars that had been "tuned" on e85 by someone who "knows" how to tune, and felt they were absolute garbage! my neighbors friend had his n/a vega tuned on e85 by someone who "knew" what they were doing and it "blew up" so they both think the stuff is voodoo now.

when I build an engine I try to make a combo that will make good power with less timing, more compression, on lower octane fuels by focusing on quench and squish areas. I found that on my most recent engine I built for myself that when running e85, I ran much less timing and fuel at idle and cruise then people believe is necessary because I was running it leaner (which gave it a "quicker" burn) but didn't ping or knock (what I believed) because I was running very tight squish (bout .038) and full quench pads on my g-head (and flat top pistons). but when actually making boost/power I did have to fatten it up quite a bit below maximum torq to keep it from knocking (so I guess I should say more stable burn instead of slower?). its the different afr's that make e85 act very differently, which can be a rewarding or defeating game to play...

so instead of blasting each other, what is your reasoning that knock went away when adding e85 to the mix? im just trying to gain knowledge through this forum, id like to hear what you have to say...