TU and F4 Camshaft Follow-on Discussion

[glhs875]

With the previous engine combination I ran everywhere from 8.35:1- 8.78:1; The higher CR iteration had better low end torque (slightly) but a narrower tuning window (also slightly). By changing chamber volume and selecting the desired stack thickness of the MLS head gasket you can make small changes to the CR.
With the header and smallish turbo it would spool up fast either way, too fast actually, as it had too much bottom end.

The new engine is presently at 8.53:1. The newest cam I had made I narrowed the LSA 2 more degrees (112). My plan was to kill off some low end torque for traction, and push the rpm up and make the car work more on the top half of the track. I was concerned that with the bigger turbo and cam I would have trouble getting it spooled-up against the convertor as the car needs to "leave" at about 3800rpm, and at least 7-9psi boost. Turns out I am able to load the convertor to about 3300rpm with the turbo charge pipe disconnected, as in all motor.
I don't know how it would spool with a manual trans, but it takes a loose convertor to make it all work now. I run the cam advanced between 2-5 degrees, depending on conditions.

I know you said the LSA of your current cam is 112 degrees. Is the intake centerline also at 112? If so, are you advancing the cam 2-5 degrees from the 112 or some other number?

[acannell]

okay I measured my exhaust pressure. At the moment I only have two numbers, but technically I can log data at 10hz for exhaust pressure. Ill do that when I have a higher power/boost level so things are more interesting.

but anyhoo, peak boost was 16.5psi, peak exhaust pressure was 22.5 psi, so a pressure ratio of 1.36:1? this is measured a couple inches from the head on the exhaust primary

http://www.turbododge.com/forums/f4/...ml#post3571297

does this seem about right for a stock swirl head, cam, tubular header, and stage 1 wheel in a 0.63? how much data do we actually have for backpressure measurements on TD's?

[moparzrule]

What swingvalve and exhaust? Bottlenecks don't just stop at the turbo, you can have higher/lower backpressure from stuff after the turbo.

What header are you running?

That sounds about right though, assuming you have good flow after the turbo, actually pretty good with a stage 1 wheel. But then again it is only 16.5 boost. The higher you go the higher the ratio will probably get.

[acannell]

What swingvalve and exhaust? Bottlenecks don't just stop at the turbo, you can have higher/lower backpressure from stuff after the turbo.

What header are you running?

That sounds about right though, assuming you have good flow after the turbo, actually pretty good with a stage 1 wheel. But then again it is only 16.5 boost. The higher you go the higher the ratio will probably get.

The header is a homebuilt mandrel tubular 4 to 1 with 14" to 19" primaries, the swingvalve is whatever size is biggest without modification before a 3" is. The exhaust is 3" straight to the bumper.

Yes I think the 25psi data will be alot more interesting than the 16.5 psi data. Especially if I plot the boost vs backpressure, and we can see if its linear or starts going straight up at some point.

[moparzrule]

I'm almost positive with the stage 1 turbine you'll get to atleast 1.5:1 at 25 psi. The stock head is helping keep the backpressure down though right now, as that's more of a restriction than the turbine wheel. If you had a ported head I suspect you'd already be at 1.5:1 at 16psi.

[Shadow]

how much data do we actually have for backpressure measurements on TD's?

Dic! There are Some #'s from the higher powered cars, but even then, there are those that don't even post their #'s when asked

Crazy that your drive pressure is already that high! (even with the .63!) and with a Stock head. This would be a Great time to test exhaust mads and confirm that even at your power level and with low boost, the 3" mandrel (right off the S/V) IS the Greatest gain for bringing drive pressure Down

[acannell]

Dic! There are Some #'s from the higher powered cars, but even then, there are those that don't even post their #'s when asked Crazy that your drive pressure is already that high! (even with the .63!) and with a Stock head. This would be a Great time to test exhaust mads and confirm that even at your power level and with low boost, the 3" mandrel (right off the S/V) IS the Greatest gain for bringing drive pressure Down

This brings up an question. Sort of an academic one for several reasons, but hey until we get some numbers from somebody to discuss then I'll take the mic (eeeyooowweee) For any given pressure ratio (speaking here of exhaust backpressure over boost pressure, not compressor map things), there are multiple possibilities as to power level. For instance, my car has 1.36:1, so may some 600whp V8 (reading the turbo mustang forums seems to show turbo V8's in that range of pressure ratios). Not enough info in it by itself to mean anything. Then, getting more specific, specifying a pressure ratio at a specific boost pressure doesn't seem to help much either. For instance you could still have an engine making 1000whp at 16.5psi boost and 22.5psi backpressure flowing 5 times as much air as my engine, and probably call it a wild success given real world limitations of how big you can make all the tubes and holes. So this leads me to think that the only meaningful things that one can conclude about pressure ratio is "lower is better" and "making holes/tubes bigger/smoother makes it lower ". Is there anything else? Yes this would be a great time to swap swingvalves. To do so I'll have to either make one from scratch or take out my tubular header, because my header hugs the 2.5" SV within a mm or so. So I guess that means I'm going to make one.

[glhs875]

Dic! There are Some #'s from the higher powered cars, but even then, there are those that don't even post their #'s when asked

Crazy that your drive pressure is already that high! (even with the .63!) and with a Stock head. This would be a Great time to test exhaust mads and confirm that even at your power level and with low boost, the 3" mandrel (right off the S/V) IS the Greatest gain for bringing drive pressure Down

Yes! That would be some very interesting data by getting the backpressure readings after a nice mandrel bend downpipe was installed keeping everything else the same for the test!

[Warren Stramer]

I know you said the LSA of your current cam is 112 degrees. Is the intake centerline also at 112? If so, are you advancing the cam 2-5 degrees from the 112 or some other number?

Sorry for the delay, I've be pre-occupied. In the case of my current cam, I'm running it 2-5 advanced from 112.

[Shadow]

So after all of this, and getting back to original topic for the title of this thread. It would seem that the R5 has Less duration than the F4, but More lift.

Does everyone get this Same conclusion after reading through all of this? Or does this confuse things More? lol

[acannell]

So after all of this, and getting back to original topic for the title of this thread. It would seem that the R5 has Less duration than the F4, but More lift.

Does everyone get this Same conclusion after reading through all of this? Or does this confuse things More? lol

Was something said in the thread that gave more info about the R5 than what Chris originally posted? BTW is that on intake and exhaust or just one?

So I'll take a stab at trying to understand the consequences of increasing lift and decreasing duration, all other things remaining the same, on a hypothetical cam.

This would shorten the valve event in time, but without knowing the specific relative change, its not clear how the "area under the curve" would change. It could stay the same, decrease, or increase.

So without knowing that, the intentions and results are less clear. But lets say for discussions sake that the area remains the same. Does the area remaining the same actually translate into the same mass of air being transferred, just over a shorter period of time? Or do the flow physics not work that way? How sensitive are the results to RPM?

Shortening the event while maintaining a fixed area could allow for less overlap and therefore less sensitivity to exhaust backpressure, correct? Seems like the intent there would be to take advantage of mechanical changes which allow an increase in intake flow, but without a proportional increase in exhaust flow.

????

[moparzrule]

So after all of this, and getting back to original topic for the title of this thread. It would seem that the R5 has Less duration than the F4, but More lift.

Does everyone get this Same conclusion after reading through all of this? Or does this confuse things More? lol

How have you determined that? Were specs posted that I missed? We really need the F4's specs at .050 to determine anything. Duration at .006 is nearly worthless, and comparing a cam .050 to .050 is still also not that great (although gets you a better idea than .006).

I don't think you have enough info to come to any conclusions. I can tell you this, on the R5 cam, at .010 cam lift the durations are 10 degrees apart but at .200'' the durations are the same on intake/exhaust. Until we have a cam card for the F4 you will never be able to accurately compare anything.

[Shadow]

Was something said in the thread that gave more info about the R5 than what Chris originally posted? BTW is that on intake and exhaust or just one?

Nothing else was said AFAIK, i'm going off what info we have on the table Now, and that would be for Both.

So I'll take a stab at trying to understand the consequences of increasing lift and decreasing duration, all other things remaining the same, on a hypothetical cam.

This would shorten the valve event in time, but without knowing the specific relative change, its not clear how the "area under the curve" would change. It could stay the same, decrease, or increase.

So without knowing that, the intentions and results are less clear. But lets say for discussions sake that the area remains the same. Does the area remaining the same actually translate into the same mass of air being transferred, just over a shorter period of time? Or do the flow physics not work that way? How sensitive are the results to RPM?

Shortening the event while maintaining a fixed area could allow for less overlap and therefore less sensitivity to exhaust backpressure, correct? Seems like the intent there would be to take advantage of mechanical changes which allow an increase in intake flow, but without a proportional increase in exhaust flow.

????

In a Nutshell, and from what I understand, when you Increase lift, without any other change to cam profile, you allow for more power without changing the rpm (powerband). So More power Potential without moving powerband to the right. This will only work (actually make more power) IF all of the other components in the build can Support the added lift of the cam. Usually, when lift is Increased, Duration is Increased as well.

Increasing Duration, on the other hand, Directly effects the rpm that the motor operates in and moves the curve to the right (higher in rpm range) by allowing the motor to Breath More from the valve event (time) being increased.

So Increasing Duration, increases the time the valve stays open. Increasing lift, Does Not increase time the valve stays open, it just opens the valve More in that same time frame.

[Shadow]

How have you determined that? Were specs posted that I missed? We really need the F4's specs at .050 to determine anything. Duration at .006 is nearly worthless, and comparing a cam .050 to .050 is still also not that great (although gets you a better idea than .006).

I don't think you have enough info to come to any conclusions. I can tell you this, on the R5 cam, at .010 cam lift the durations are 10 degrees apart but at .200'' the durations are the same on intake/exhaust. Until we have a cam card for the F4 you will never be able to accurately compare anything.

I determined this from the info contained within this thread. I simply asked the Q to see IF anyone else is paying attention

[moparzrule]

Well like I said I might have missed something. I wasn't really watching the thread like a hawk or anything.

Some specs of the R5 cam for those interested-

[Shadow]

Way to break the Ice Bro! I should be able to get some accurate specs for comparo when I dial in the next F4 cam on the 2.5 that's sitting in the shop.

[acannell]

In a Nutshell, and from what I understand, when you Increase lift, without any other change to cam profile, you allow for more power without changing the rpm (powerband). So More power Potential without moving powerband to the right. This will only work (actually make more power) IF all of the other components in the build can Support the added lift of the cam. Usually, when lift is Increased, Duration is Increased as well.

Increasing Duration, on the other hand, Directly effects the rpm that the motor operates in and moves the curve to the right (higher in rpm range) by allowing the motor to Breath More from the valve event (time) being increased.

So Increasing Duration, increases the time the valve stays open. Increasing lift, Does Not increase time the valve stays open, it just opens the valve More in that same time frame.

Ah so I have a question (raises hand)

When we say something like "the powerband moves up in rpm", what that really means is the peak power band moves up in rpm. It doesn't necessarily mean there is less power at some original lower rpm, than there was before, does it? So the result ends up being more power everywhere, with the peak moved up in rpm. Yes?

For instance, increasing duration would not reduce the power at a lower rpm, would it? The only reason I could see that happening is if the intake tract is tuned in a way which requires a certain valve timing to make use of the waves somehow, and by actually opening the valve longer that relationship is lost or reduced.

So with the case of a heavily modified intake and ported head, any hope that the intake tract is tuned a certain way is pretty much lost, yes? So in that case, it becomes purely a choice of where peak power is desired.

For drag racing, where is it ideal to locate peak power? That would depend alot on the transmission and traction yes?

[4 l-bodies]

Way to break the Ice Bro! I should be able to get some accurate specs for comparo when I dial in the next F4 cam on the 2.5 that's sitting in the shop.

I'm guessing those are Cam-Pro numbers, which would mean a poor comparison to real engine #'s. I have Cam-Pro #'s and degreed the same cam in by hand and you would have thought you were comparing two different camshafts. IMO, compare Cam-Pro to Cam-Pro or two camshafts degreed in by hand is only way to compare apples to apples.

[acannell]

I'm guessing those are Cam-Pro numbers, which would mean a poor comparison to real engine #'s. I have Cam-Pro #'s and degreed the same cam in by hand and you would have thought you were comparing two different camshafts. IMO, compare Cam-Pro to Cam-Pro or two camshafts degreed in by hand is only way to compare apples to apples.

can you explain this further? I can understand why measuring the lobe does not translate directly into valve position depending on the multiplication of the follower. But why would cam pro measurements vary from one cam pro to the next? How does the cam pro work?

And why would degreeing the cam affect how well you can measure it? Can you analyze the cam geometry independent of an engine entirely?

[4 l-bodies]

Ah so I have a question (raises hand)

When we say something like "the powerband moves up in rpm", what that really means is the peak power band moves up in rpm. It doesn't necessarily mean there is less power at some original lower rpm, than there was before, does it? So the result ends up being more power everywhere, with the peak moved up in rpm. Yes?

For instance, increasing duration would not reduce the power at a lower rpm, would it? The only reason I could see that happening is if the intake tract is tuned in a way which requires a certain valve timing to make use of the waves somehow, and by actually opening the valve longer that relationship is lost or reduced.

So with the case of a heavily modified intake and ported head, any hope that the intake tract is tuned a certain way is pretty much lost, yes? So in that case, it becomes purely a choice of where peak power is desired.

For drag racing, where is it ideal to locate peak power? That would depend alot on the transmission and traction yes?

Asa,
What I have found is running aftermarket camshafts is there is a definite loss of low end torque in lower RPM band, then of course "hopefully" there will always be a crossover point (RPM) where larger cam will be overtake the smaller camshaft and make it worthwhile.

For example it was found that Taft S2 gives up like 20 lb/ft down low (below 3500 RPM), approaches stock cam torque by 4000-4500 RPM and adds another 20 HP and 10 lb/ft above 4700. The larger S3 lost 30+ lb/ft below 4000 RPM. Then above 4700 RPM, it crushes the stock cam!

Many times what happens in not well thought out powertrains is powerband becomes tighter or more narrow because rest of powertrain isn't up the the task of increased RPM with the larger duration camshaft. Could be rod ratio, could be valvetrain limitations, turbo, gearing, converter, Say for example running a large duration camshaft in an engine that doesn't want to run much RPM, or tiny duration camshaft in a high RPM engine. Probably not a good combo, either way.

A perfect example of a not very well thought out powertrain was an old friends 351 4bbl (4V) Cleveland Mach 1 Mustang 25-30 years ago. Put in much bigger camshaft, and slightly higher stall converter, single plane manifold, along with not very deep gear. The vehicle was real dog until 4800 RPM. Way too big of ports for that size motor, not enough gear, and probably needed a looser converter. Very narrow powerband. From 4600 to 6400 it pulled pretty good, but then it was over. Made for a boring and lazy car to drive on the street. His buddies 351 Cleveland 2BBL headed Grande Mustang would eat it alive on the street. At the track, the 4V headed 351 would prevail, because he was always in that very narrow powerband. My 69 Z-28 was also another low torque dog. Huge duration factory solid lifter camshaft. At least that had a much larger powerband. Not much below 4000 RPM, then WOW! The factory knew it was going to need deep gearing, so they came with 3.73 gears from factory. It needed an even deeper gear. That 302 needed 4.56/4.88 gears to really wake it up. Needed RPM to keep in correct powerband. Same deal with the Ford Boss 302 and the Boss 429 Mustangs.

IMO, when selecting a camshaft, there are definite compromises to be considered, just like turbo selection. Bigger isn't always better. It will almost always effect something like low RPM torque, ecomomy, driveability, emissions, powerband, valvetrain life, etc. It also obviously has many positives too. That is one reason why turbo and NA used a different camshaft profile. Compromises...

Todd