Cam tuning info and guide

[D-Dayve]

On four stroke engines, it is important to realize that the cam rotates once for every two rotations of the crankshaft.

Volumetric efficiency is based on cylinder fill. If a 2.0L engine is filled with 2.0L of an air/fuel mixture, we say its volumetric efficiency is 100%. If a 2.0L engine fills with 3.0L of an air/fuel mixture, we say its volumetric efficiency is 150%. A forced induction engine will have a larger than 100% volumetric efficiency since the intake charge and combustion chamber are being pressurized. A naturally aspirated engine can also have a slightly larger than 100% volumetric efficiency, but it will only happen for a short duration, and is usually only in the peak of the powerband.

The art of designing camshaft profiles is meant to increase the volumetric efficiency in the RPM range that the customer requires. Camshafts don’t make magical horsepower from nowhere, they simply move the powerband around by changing the volumetric efficiency to attain the desired results.

The four strokes of the engine are:
Exhaust
Intake
Compression
Combustion
**The “start” is not important because it’s a CYCLE, meaning it repeats**

Looking at a camshaft, the sequence would be as follows:
The exhaust lobe pushes open the exhaust valve and the piston comes up to push the exhaust out, then starts to close. The intake starts to open, just as the exhaust is closing, piston goes down, and the intake valve closes. Then both valves stay closed for the compression and combustion strokes. This means that the first lobe to come through the rotation will be the exhaust lobe, immediately followed by the intake lobe.

Overlap is the point where the exhaust valve is closing, and the intake valve is just opening.

To increase overlap, you have to RETARD the EXHAUST, and/or ADVANCE the INTAKE.
To reduce overlap, you have to ADVANCE the EXHAUST, and/or RETARD the INTAKE.

Simple cam tuning rules for NATURALLY ASPIRATED engines:
Advancing both cams => more low-RPM power, less high-RPM power
Retarding both cams => more high-RPM power, less low-RPM power
Less overlap => more low-RPM power, less high-RPM power
More overlap => more high-RPM power, less low-RPM power

In a naturally aspirated engine, the extra overlap is called "scavenging". Scavenging is using the out-flowing exhaust to help draw in the next intake charge (partially causing lumpy idle).

Simple cam tuning rules for BOOSTED engines:
Advance intake and exhaust => more low-RPM power, less high-RPM power
Retard intake and exhaust => more high-RPM power, less low-RPM power
Less overlap => lower EGTs, faster turbo spool, less fuel
More overlap => higher EGTs, slower turbo spool, more fuel

Boosted engines don’t like overlap. The incoming cold air and fuel cools down the outgoing exhaust charge, condensing the exhaust gasses. This is VERY counter-productive in a turbo application since the engine needs no help from scavenging to fill the cylinder. I've heard this being called "turbo chill".

Cool, condensed gasses in the same space push less hard on the turbo, causing lag. HOT gasses are better at spooling the turbo, thus the advanced exhaust timing to open the valve sooner in the power stroke. This steals some of those hot, expanding exhaust gasses to help spin the turbo a little faster. When the piston is near the bottom of the bore, hardly any energy is going into rotating the crank anyway, so stealing expanding gasses won’t hurt anything. The retarded intake just helps cut down the overlap further.

Retarding overall cam timing:
Retarding overall cam timing is better for high-RPM power. This is because the valves are closing later. The intake valve is closing AFTER the piston has started to travel back up the bore for the start of compression stroke. This is terrible at low RPM because the intake air velocity is low, and air that was once in the cylinder is now being pushed back into the intake manifold and causing turbulence.

At high-RPM, the rules change. Air has weight, and thanks to Sir Issac Newton, we know that once it is moving, it doesn’t want to stop moving. This means that the air can continue to flow into and fill the cylinder, EVEN AFTER the piston has begun to travel UP the cylinder bore. This can allow an engine to exceed 100% volumetric efficiency, if even by a small amount.

Advancing overall cam timing:
Advancing overall cam timing is better for low-RPM power. This is because the valves are closing a little sooner. The intake valve is closing AT or NEAR when the piston is at the bottom of the bore for the start of the compression stroke. This is great at low RPM because the intake air velocity is low and easily affected by changes in the direction of piston movement in the engine. Almost as soon as the piston gets to the bottom of the bore on the intake stroke, the valve gets slammed shut so no air can escape as the piston begins to travel back up the cylinder on the compression cycle.

At high-RPM, this may become a restriction since the air has inertia and responds a little slower to pressure changes, potentially choking the air flow to the engine a little.

Conclusion:
This information is aimed at allowing tuners to understand what happens when cam timing is altered. When a larger duration camshaft is being installed, unless the lobe centerlines have been changed, the overlap will be increased. If installing larger camshafts in a turbo application, advancing the exhaust and retarding the intake will reduce the inherent increase in overlap caused by upgrading to a larger profile. Most cam grinders, especially regrinders, put the new profile in the same position as the old profile because it is easier, or the only way possible. This has to be changed when the cams are installed in an engine to attain the desired result.

A forced-induction engine should idle smooth when properly tuned, and a naturally aspirated engine should be “lumpy” and have a lope if it is tuned aggressively towards the high-RPM range. If a forced induction engine is loping at idle, fuel is being wasted, turbo spool time is being increased, and power is being lost.

I know this is a lot of info, but I wanted to write this in a way that it would be informative for someone who is a novice, or someone who is a full-on tuner, wanting some concrete info on how to tune cams.

-Dave Atchison

 

[D-Dayve]

I have this posted on *another forum*, but I wanted to share this with this community as well. I hope it's useful enough to maybe become a sticky as this seems to be a fairly frequently asked question.

If anyone needs any help or would like some pointers that aren't available in this post, please feel free to PM me. I was a cam grinder for 7 years, and designed several N/A and boosted profiles. I also worked at a shop dyno-tuning cars both a/f ratio, cam gears, and several other aspects.

An important thing to note is that if you are tuning your cam gears after you've tuned your air-fuel ratio, you have to re-tune your fuel because the change in air-flow characteristics will change your air-fuel ratio.

 

[cuel]

Thanks Dayve. Hopefully we can get this stickied either here or in the general mkiii section.

 

[suprahero]

Thanks Dave, and for those of you that don't know him, he has answered numerous questions for me reguarding my cam's on my 1jz. He's a little smarter than I am, o.k. he's a whole lot smarter than I am. Thanks again Dave, Jay

 

[suprahero]

Dave if I remember correctly, I had my exhaust advanced about 8degrees and my intake retarded about 4 degrees and this seemed to be the best for my application. I also noticed that changing the intake side didn't really affect that much. Is this normal or should I notice a substantial change when adjusting the intake side?

 

[Ma70.Ent]

Saw this on SF. Stickied!

 

[Doward]

A couple notes:

1) Volumetric efficiency = (Actual air ingested) / (theoretical air ingested) * 100%

A 191ci motor spinning 6400 rpm @ 14.7psi boost should be ingesting 707.407cfm of air. If it is actually ingesting 656.436cfm of air, we say the engine's VE at that point is 92.79% volumetric efficiency.

The *only* way to have greater than 100% VE is to have a tuned intake/exhaust system that allows proper air wave pulse harmonics IN ADDITION TO the actual pressurization of the intake.

2) Overlap is the period that both exhaust and intake valves are open. (Just a little clarification)

3) Boosted engines not liking overlap is a myth. Boosted engines with abnormally high exhaust pressures not liking overlap, is truth.

4) The statement "A forced-induction engine should idle smooth when properly tuned, and a naturally aspirated engine should be “lumpy” and have a lope if it is tuned aggressively towards the high-RPM range. If a forced induction engine is loping at idle, fuel is being wasted, turbo spool time is being increased, and power is being lost." is wrong. See Duane Stephens for proof of concept.

Just wanted to clarify a few incorrect statements. The generalizations of advancing/retarding the camshafts are crude, but correct enough for most.

*edit* This - In a naturally aspirated engine, the extra overlap is called "scavenging". Scavenging is using the out-flowing exhaust to help draw in the next intake charge (partially causing lumpy idle). - is incorrect. Scavenging is using proper exhaust pulse harmonics to help draw out spent gases from the combustion chamber, at the moment overlap is present - this low pressure inside the combustion chamber is what draws the intake air/fuel mixture in.

 

[D-Dayve]

Dave if I remember correctly, I had my exhaust advanced about 8degrees and my intake retarded about 4 degrees and this seemed to be the best for my application. I also noticed that changing the intake side didn't really affect that much. Is this normal or should I notice a substantial change when adjusting the intake side?

That's pretty much right on. Bigger (performance) cams generally need a bit more advance on the exhaust and a little more retard on the intake in order to cut the overlap down more. The bigger the cam profiles, the larger the inherent overlap. If you tune an engine for a certain set of cams, then put in larger cams, you'll probably end up increasing whatever you did with the smaller cams (assuming they are ground on the same centerline).

Believe it or not, the exhaust is where most of the power is made on performance cams. Of course, you do need a larger intake in order to flow more air, but the power gains are usually found in the exhaust. If you were to just upgrade one cam in a DOHC setup, the exhaust would make you more horsepower compared to an equal increase in size on just the intake camshaft.

So, to clarify, most of the gains in performance camshafts are found in the exhaust, but at a certain point, the intake becomes the weak link and must be increased as well.

 

[D-Dayve]

A couple notes:

1) Volumetric efficiency = (Actual air ingested) / (theoretical air ingested) * 100%

If you want to be picky, that's correct, but the "theoretical air ingested" is usually the displacement of the engine (meaning 100% of the engine's volume). Since the theoretical displacement of the engine is 100%, if you were running boost, it would be much easier to be running higher than 100% volumetric efficiency. Even naturally aspirated engines can reach over 100% volumetric efficiency. That's all about what performance camshafts do. They don't create power, they re-tune your engine to be more volumetrically efficient at a certain point. It's not uncommon for an N/A engine to have a volumetric efficiency of even 106% at a certain point in the RPM.

A 191ci motor spinning 6400 rpm @ 14.7psi boost should be ingesting 707.407cfm of air. If it is actually ingesting 656.436cfm of air, we say the engine's VE at that point is 92.79% volumetric efficiency.

This is correct ONLY if you mean that 14.7psi is atmospheric pressure (your boost gauge = 0). If you mean 14.7psi on a boost gauge, you are incorrect since that's psig (your boost gauge = 14.7)

psia = the normal pressure around us compared to a vacuum (a psia gauge would read 14.7 at rest)
psig = PSI of the gauge you are reading compared to atmosphere (a psig gauge would read 0 at rest)

I think this is where the confusion lies.

The *only* way to have greater than 100% VE is to have a tuned intake/exhaust system that allows proper air wave pulse harmonics IN ADDITION TO the actual pressurization of the intake.

I completely disagree. Guys who have been telling me this are usually tuning a megasquirt where VE has almost become an abstract concept which changes whenever the injector size is changed. The VE in a megasquirt is more closely related to injector dutycycle.

2) Overlap is the period that both exhaust and intake valves are open. (Just a little clarification)

Agreed. Looking at the stroke sequence above, it's where the exhaust is just closing, and the intake is just opening.

3) Boosted engines not liking overlap is a myth. Boosted engines with abnormally high exhaust pressures not liking overlap, is truth.

There are all sorts of arguments to this. What I'm saying is what's true for 99.9% of all street driven cases that would be found on this or other forums like it. Engines that run abnormally high (for street use) RPMs utilize overlap, even in boosted applications. If you want to rev your engine to the moon, overlap and boost go quite well together. I haven't seen a street-driven car that was able to justify this.

Almost every turbo engine I've ever seen has abnormally high exhaust pressures. It's what's know as the "turbo drive pressure", and is usually VERY close to your boost pressure (although a little higher). Turbos aren't magical devices that create pressure from nothing. What you are doing is using the expanded exhaust gasses (which are mathematically larger due to heat expansion) to blow the significantly cooler (and mathematically smaller) intake charge in. If your turbo was producing 20psi of boost on the intake, you'd be seeing something like 22 psi or more of exhaust drive pressure in the manifold. To me, this constitutes "abnormally high exhaust pressure".

4) The statement "A forced-induction engine should idle smooth when properly tuned, and a naturally aspirated engine should be “lumpy” and have a lope if it is tuned aggressively towards the high-RPM range. If a forced induction engine is loping at idle, fuel is being wasted, turbo spool time is being increased, and power is being lost." is wrong. See Duane Stephens for proof of concept.

I know Duane Stephens, his phone number is in my phone. I'm one of the electricians who does the electrical work at the CNC shop he works at. I haven't had this conversation with him yet, but I have spoken to him in depth about tuning, and we usually tend to agree. He's also in a different class than 99.999% of the people on here.

I'm not making up these concepts, I've proven them on a dyno, time and time again on countless engines from domestic V8s to Hondas.

I'd like to emphasize the fact that I'm talking to the 99% majority, not the 1% minority where the rules don't apply the same.

*edit* This - In a naturally aspirated engine, the extra overlap is called "scavenging". Scavenging is using the out-flowing exhaust to help draw in the next intake charge (partially causing lumpy idle). - is incorrect. Scavenging is using proper exhaust pulse harmonics to help draw out spent gases from the combustion chamber, at the moment overlap is present - this low pressure inside the combustion chamber is what draws the intake air/fuel mixture in.

Harmonics have very little to do with what I'm talking about. We're not designing intake and exhaust manifolds, we're talking about cam timing. Pressure equalization is what we're dealing with. Harmonics have to do with pressure waves at different reflective frequencies, based on the volume of the "container" in question... meaning the exhaust or intake. That's why flow testing is used, rather than harmonic sound waves to measure the value of a given intake or exhaust manifold... Not to say that harmonics don't play a part in the system though.

Doward, I thank you for contributing to this thread, and I hope that we and others can continue this discussion in a meaningful and mature manner.

-Dave

 

[bowsercake]

I read your information from Supra Forums before. I am running 9mm cams and I do not have cam card so I could not degree the cam. But I found that running the Exhaust 4* advanced and the Intake *2 retarded to reduce overlap helped a lot. I had too much overlap at first and the car sounded aggressive but it didn't run well.

Thanks for your information. I will be tuning my cams on a dyno some time in the near future.

 

[MrWOT]

All of the above D-Dayve posted is correct, if you're working on a bone stock setup. Doward is correct if you have a system in which the exhaust backpressure is greatly reduced through either a big turbine setup or a specialized low reversion setup. But most folks don't use a ~>.80 a/r turbine and associated parts, or cant make/cant afford the cams/headwork/exhaust manifold/wastegates/exhaust neccissary to use high overlap with a ~<.80without jacking up your EGTs. You are wasting fuel if you have a loping idle, but that doesn't mean it won't make more power.

The rod/stroke ratio of the 7M actually lends it to being a bit more tolerant of larger cams.

 

[Doward]

If you want to be picky, that's correct, but the "theoretical air ingested" is usually the displacement of the engine (meaning 100% of the engine's volume). Since the theoretical displacement of the engine is 100%, if you were running boost, it would be much easier to be running higher than 100% volumetric efficiency. Even naturally aspirated engines can reach over 100% volumetric efficiency. That's all about what performance camshafts do. They don't create power, they re-tune your engine to be more volumetrically efficient at a certain point. It's not uncommon for an N/A engine to have a volumetric efficiency of even 106% at a certain point in the RPM.

It's not about being 'picky' - it's about being correct. Engine tuning still has this incredible stigma of being a 'black art' and that is so far from the truth, that it really gets on my nerves. Camshafts do create power by optimizing delivery of air/fuel into the combustion chamber at certain RPMs. As I explained before:

The *only* way to have greater than 100% VE is to have a tuned intake/exhaust system that allows proper air wave pulse harmonics IN ADDITION TO the actual pressurization of the intake.

To further elaborate, see my next point.

This is correct ONLY if you mean that 14.7psi is atmospheric pressure (your boost gauge = 0). If you mean 14.7psi on a boost gauge, you are incorrect since that's psig (your boost gauge = 14.7)

psia = the normal pressure around us compared to a vacuum (a psia gauge would read 14.7 at rest)
psig = PSI of the gauge you are reading compared to atmosphere (a psig gauge would read 0 at rest)

I think this is where the confusion lies.

I apologize, but again, you are wrong. You live in a constant pressure of ~14.69 psi, depending on your altitude and current barometric pressure. An NA engine is always seeing ~14.7 psi. This is the absolute pressure seen. When you see 14.7psi on a boost gauge, you are in fact seeing 14.7(boost) + 14.7(absolute atmospheric) = 29.4psi of absolute pressure in the intake. This is why you need a 2 bar map sensor, to run 14.7psi on a turbo motor.

I completely disagree. Guys who have been telling me this are usually tuning a megasquirt where VE has almost become an abstract concept which changes whenever the injector size is changed. The VE in a megasquirt is more closely related to injector dutycycle.

Again, VE IS NOT injector duty cycle. Many standalone systems do not report the 'true' VE of the engine, they only report a number that can be used to 'fudge' the fueling of your engine. Some people are ok with that (as hey, the engine runs doesn't it?) but again - there is right and there is wrong. I'm a firm subscriber in knowing exactly what is going on, and not resorting to 'black magic' for fueling

Just to re-iterate, the only way to go beyond 100% VE is using pulse harmonics to pull the current air charge in quicker, using the fluid's inertia to help.

Agreed. Looking at the stroke sequence above, it's where the exhaust is just closing, and the intake is just opening.

Yep - just wanted to clarify a little

There are all sorts of arguments to this. What I'm saying is what's true for 99.9% of all street driven cases that would be found on this or other forums like it. Engines that run abnormally high (for street use) RPMs utilize overlap, even in boosted applications. If you want to rev your engine to the moon, overlap and boost go quite well together. I haven't seen a street-driven car that was able to justify this.

Almost every turbo engine I've ever seen has abnormally high exhaust pressures. It's what's know as the "turbo drive pressure", and is usually VERY close to your boost pressure (although a little higher). Turbos aren't magical devices that create pressure from nothing. What you are doing is using the expanded exhaust gasses (which are mathematically larger due to heat expansion) to blow the significantly cooler (and mathematically smaller) intake charge in. If your turbo was producing 20psi of boost on the intake, you'd be seeing something like 22 psi or more of exhaust drive pressure in the manifold. To me, this constitutes "abnormally high exhaust pressure".

My jaw hit the floor when I read this. Incredibly wrong. You are not using 'expanding gases' to drive the turbine!! You are using exhaust gas VELOCITY to drive the turbine. NOT heat or pressure! Yes, the gas is expanding (or contracting, if you put your turbo further away) so you take that into account.

PRESSURE IN A FLOWING SYSTEM IS RESISTANCE TO FLOW - Always. You have to look at your entire engine as system, pick a point that you want maximum power at (in my case, I'm building mine to produce maximum torque @ 5000rpm, with a 7200rpm ceiling)

The stock turbo (and any other 'small' exhaust side turbo) spools quickly because the velocity of exhaust gas is high, at a low rpm. Once the exhaust velocity begins to disrupt the laminar boundary flow, you hit the 'choke' point of your exhaust setup. You want this choke point to happen right before you hit maximum rpm of the engine.

I know Duane Stephens, his phone number is in my phone. I'm one of the electricians who does the electrical work at the CNC shop he works at. I haven't had this conversation with him yet, but I have spoken to him in depth about tuning, and we usually tend to agree. He's also in a different class than 99.999% of the people on here.

I'm not making up these concepts, I've proven them on a dyno, time and time again on countless engines from domestic V8s to Hondas.

I'd like to emphasize the fact that I'm talking to the 99% majority, not the 1% minority where the rules don't apply the same.

The rules *always* apply the same. Whether one chooses to adhere to them, is up to them.

Harmonics have very little to do with what I'm talking about. We're not designing intake and exhaust manifolds, we're talking about cam timing. Pressure equalization is what we're dealing with. Harmonics have to do with pressure waves at different reflective frequencies, based on the volume of the "container" in question... meaning the exhaust or intake. That's why flow testing is used, rather than harmonic sound waves to measure the value of a given intake or exhaust manifold... Not to say that harmonics don't play a part in the system though.

Harmonics have everything to do with the camshaft. The entire point of the intake pulse tuning is to reflect the wave back to the valve at the moment it opens, is it not? How can you say harmonics has little to do with the camshaft? The camshaft CONTROLS the harmonics you seek!

Doward, I thank you for contributing to this thread, and I hope that we and others can continue this discussion in a meaningful and mature manner.

-Dave

No problem. With so many variables in an engine, it can get difficult to keep track of them all. I take a very systematic approach to engine design, building, and tuning. I only want to make sure the correct information is presenting. After all, it's up to the user to decide what is in his/her best interest

All of the above D-Dayve posted is correct, if you're working on a bone stock setup. Doward is correct if you have a system in which the exhaust backpressure is greatly reduced through either a big turbine setup or a specialized low reversion setup. But most folks don't use a ~>.80 a/r turbine and associated parts, or cant make/cant afford the cams/headwork/exhaust manifold/wastegates/exhaust neccissary to use high overlap with a ~<.80without jacking up your EGTs. You are wasting fuel if you have a loping idle, but that doesn't mean it won't make more power.

The rod/stroke ratio of the 7M actually lends it to being a bit more tolerant of larger cams.

LOL, that was vague enough If you want high power, with high reliability, you must ensure everything works together. I didn't want to get into the mechanics of the 7M, but yes, the R/S ratio does work pretty well with a larger cam. And yes, you are correct - reducing backpressure (either through larger turbine area, or optimized head/cams/manifolds) goes hand in hand with increasing power without through EGTs through the roof.

 

[D-Dayve]

Well, I can't put this any simpler than:
100&#37; VE means a 3.0L engine uses 3.0L of air over a complete cycle (2 revolutions). If you run boost, you can get say 4.0L of air into a 3.0L engine, meaning you have a VE of 133.3%. That's the way it is, plain and simple. If you don't agree with me, fine, but if you do a little research (wikipedia says: "Volumetric efficiencies above 100% can be reached by using forced induction such as supercharging or turbocharging"), and that's how I and all the tuners I've known have always understood VE. If you don't agree with me, that's fine, but it is what it is, and I can't explain it better than that.

Just to re-iterate, the only way to go beyond 100% VE is using pulse harmonics to pull the current air charge in quicker, using the fluid's inertia to help.

No, see above and research a little. There are actual volumetric efficiency charts of STOCK NA Honda engines (and I'm sure several others) that have volumetric efficiencies even up to 107%. This is because air has inertia and at higher RPMs (even in a regular, stock, street-driven motor) air continues to fill the cylinder as the piston has begun to travel up the bore, allowing an over-fill of the chamber. This is all thanks to the fact that air has weight, and thus inertia and momentum.

What you are doing is using the expanded exhaust gasses (which are mathematically larger due to heat expansion) to blow the significantly cooler (and mathematically smaller) intake charge in. If your turbo was producing 20psi of boost on the intake, you'd be seeing something like 22 psi or more of exhaust drive pressure in the manifold. To me, this constitutes "abnormally high exhaust pressure".

My jaw hit the floor when I read this. Incredibly wrong. You are not using 'expanding gases' to drive the turbine!! You are using exhaust gas VELOCITY to drive the turbine. NOT heat or pressure! Yes, the gas is expanding (or contracting, if you put your turbo further away) so you take that into account.

I don't think you're understanding what I'm saying... I'm saying that the hot EXPANDED (past tense) gasses are mathematically larger than the intake air due to the EXPANSION (because they're hotter than intake air), and they flow through the exhaust side of the turbo. Not that the gasses are expanding into the turbo if that's what you thought I said...

Harmonics have everything to do with the camshaft. The entire point of the intake pulse tuning is to reflect the wave back to the valve at the moment it opens, is it not? How can you say harmonics has little to do with the camshaft? The camshaft CONTROLS the harmonics you seek!

The intake plenum size controls harmonics. The harmonics are created by the valves opening and closing, but the camshaft does nothing to control harmonics. Harmonics are controlled by the intake plenum size, which should be calculated so as not to create a standing harmonic wave that would interfere with airflow. I'm not sure if you are actually grasping the concept of what harmonics are. Here's a website that should make more sense: http://v8soarer.com/intakerunners/index.shtml. Harmonics aren't controlled by camshafts, but by intake manifolds through calculations based on intake plenum volume, diameter, engine RPM, and displacement.

The rules *always* apply the same. Whether one chooses to adhere to them, is up to them.

I'd like to see you try out for an engine tuning job in F1. The "LAWS" always apply the same, the way in which you have to deal with them changes. It's the same reason why a super-sonic jet is shaped like an arrowhead with straight edges, and a regular jet liner has a blunt, round nose. The super-sonic jet has different rules because airflow changes at the speed of sound. Of course, this has nothing to do with engines, my point is that you have to compare apples to apples. My grandmother's Chevy Celebrity's engine uses VERY different rules for tuning than Duane's 7M.

Thanks,
Dave

 

[MrWOT]

The intake plenum size controls harmonics. The harmonics are created by the valves opening and closing, but the camshaft does nothing to control harmonics. Harmonics are controlled by the intake plenum size, which should be calculated so as not to create a standing harmonic wave that would interfere with airflow. I'm not sure if you are actually grasping the concept of what harmonics are. Here's a website that should make more sense: http://v8soarer.com/intakerunners/index.shtml. Harmonics aren't controlled by camshafts, but by intake manifolds through calculations based on intake plenum volume, diameter, engine RPM, and displacement.

It's your rod to stroke ratio that determines the wave, piston position specifically. The plenum and runners control the timing of those waves, but the cams do most definetly play a role as the valve position determines how those waves are transmitted and reflected.

 

[D-Dayve]

Yes, the cams play a role in the harmonic waves, I never said they didn't. I said they're controlled by the intake plenum and runners though.

At any rate, this has little to nothing to do with people tuning their street driven, modified, or even reasonably high performance vehicles. I'd like to keep this discussion down to cam tuning to help the average person tune their cams. I'm also here to answer any questions people have about cam tuning.

What I'm NOT interested in doing is filling this thread up with useless information that is far beyond the comprehension of someone who simply wants to dial their cams in to something other than 0 and 0. Arguing standing waves, harmonic back pulses, plenum design and rod to stroke ratio should be in another thread.

-Dave

 

[Doward]

Only problem - if you don't truly understand the mechanics behind what you are trying to accomplish, you can not possibly maximize the potential in your engine.

LOL, Wikipedia is wrong on VE, sorry I'm saying that as an engineer, not Joe Schmoe.

Just think about your calculations for a second - ((ci * rpm)/(1728 * 2)) * PR * VE = cfm of air ingested, correct?

Take this for my own 7M @ 5000rpm, 14.7psi, 97&#37; VE =
((191*5000))/(3456) * 2.0 * 0.97 = ~536cfm of air.

Now let's say we do this your way. I'm putting just under 6.0L of air into a 3.0L motor. So 197% VE. ((191*5000))/(3456) * 2.0 * 1.97 = ~1089cfm of air.

So which is it?

A link for you:
http://www.bentleypublishers.com/gallery.htm?code=GTUR&galleryId=805

Turbocharger exhaust gases. Yes, they are hotter. Also, there are less moles of gas. Less pressure there. When you talk heat, you are talking pressure. Pressure is not what you are worried about when spooling your turbo, exhaust velocity is. Period.

Another clarification: It is not the actual inertia of the air that keeps it flowing into the cylinders. Please, think for a moment:

The standard 4 stroke engine goes through 720 degrees of crankshaft rotation, to complete one cycle. During those 720 degrees of rotation, the camshaft is only open for (generally) 200-240 degrees. The air spends most of its time, sitting there, held back by the intake valve.

What does Sir Isaac tell us? Object at rest wants to stay at rest. The air DOES NOT WANT TO MOVE. You can actually stall your airflow, running a small camshaft at extremely high rpms (gee whiz, I wonder why increasing camshaft duration increases the rpm of max torque, generally speaking?).

How do we overcome the air's natural tendency to sit on its ass? Well, when the intake valve slams shut, yes, the inertia of the air tries to keep it moving. It slams into the back of the valve, and forms a pulse wave that flows back up the intake runner. Once it hits the plenum, most of the compressed air wave dissipates, but some of it actually reflects back toward the valve. You actually get between 1-4 orders of harmonics going in this whole process (I'm dumbing it down significantly here) depending on length of intake runner.

I'm not sure if you are grasping the concept. LOL, look at the link you provided - it's agreeing with me completely. Camshaft and harmonics are tied together, intrinsically I'm sorry if you want to ignore this.

You grandmother's 2.8L V6 in her Celebrity follows the same laws as an F1 engine, which follows the same laws as a Concorde, which follows the same laws as my little brother's 10 speed Huffy. They are known as 'Physics'

I *highly* suggest you get Corky Bell's book, "Maximum Boost: Turbocharger Systems" and give it a thorough read. Come back after you have done so.

I'm sorry you are not interested in discussing this (or as you put it, "filling this thread up with useless information") but my job here @ SM as an SME, is to prevent misinformation.

Besides, I'm waiting to see if MrWOT is going to sit down and give us his thoughts on all of this. So far, he's only chimed in mechanically speaking, but he's dead on the money thus far

When you are dealing with as many variables as we are talking about here, you can get extremely similar results, using different methods. The difference, IMHO, is understanding how you got your results. Fudging up numbers to cover partial misunderstanding won't cut it in my book, sorry.

 

[jdub]

What I'm NOT interested in doing is filling this thread up with useless information that is far beyond the comprehension of someone who simply wants to dial their cams in to something other than 0 and 0. Arguing standing waves, harmonic back pulses, plenum design and rod to stroke ratio should be in another thread.

-Dave

You can't look at cam timing by itself, it's only part of the equation that makes the motor work as a system. Dow is pointing that out and the info he's posting illustrates it.

Kinda important for the guy tuning his motor to realize changing one aspect will change another.

 

[Adjuster]

Interesting debate and discussion going on here.

My personal thought is the stock 7MGTE cams do a pretty good job of working with the stock motor, and stock intake etc.

Higher lift might be a good improvement, and perhaps some extended duration without too much overlap that would screw up the nice idle and low end power that this engine has to have for street use.

Personally, the best bang for the buck on this motor is just to turn up the boost and add more fuel... (Simplistic, but it's basicly a sound recipe for solid power gains on a budget, as long as the air fuel ratios are controlled, and monitored.)

I've often wondered what effects the custom FFIM's are doing to the harmonics on this motor, and if it really makes any difference in low engine speed power and tourqe. We know the short runner v/s longer runner manifolds do change low end v/s high end numbers. I'm sure the cams and any degree changes or adjustments will also affect this stuff. (But not as much as just adding more air and fuel.. )

Keep up the dialog. This is just getting interesting.


One thing to knock around here.
On my FZ1, it has a 1.0L I4 engine that will spin all day at 12,000rpm. It is a screamer! (Basicly a slightly de-tuned R1 engine.) It has subthrottles that the computer controls to both limit the peak power in the lower three gears, or under 100mph. (So you do not just nail the throttle, and end up on your ass doing the super wheelie..) The harmonics on this super high performance engine get quite LOUD at 5,000rpm. With my modified air box, the harmonics bark up under the gas tank, and it makes quite the intake roar/racket. Oh, and this NA motor with slightly less than 1000cc's of displacement puts out over 150hp. (There are quite a few bikes with 148 to 151hp at the wheel, so quite a good improvement over the 150hp crank claims stock that yield about 128 to 132hp at the wheel stock. I figure mine is somewhere in the 148rwhp area, but I have not put the bike on a chassis dyno. What is the VE on that engine LOL

Many have either zip tied them open and disconnected the servo that operates them, or they have cut down the plates in an effort to get around the lack of power in the lower gears/sub 100mph/7000rpm. I tried it with them open, and WOW it was loud. I thought something was broken for a second. Not the case, it was just harmonics. So, I tried to cut them down, allowing more air around them, but still providing a "wall" to reflect some of the harmonic pulse.. And I have found a good compromise of power, and smoother engine operation.

Yamaha has gone even farther now with variable intake stacks, and the throttlebodies. (Along with a throttle by wire setup.)

I wonder who will be the first bike maker with a completely variable cam timing setup like BMW/Nissan and others are using that removes the need for even a throttle body to regulate the air. (It is all done with the cams and valvetrain.) Should be the hot ticket for both harmonics, and max engine power from idle to redline.

 

[MrWOT]

Just think about your calculations for a second - ((ci * rpm)/(1728 * 2)) * PR * VE = cfm of air ingested, correct?

Take this for my own 7M @ 5000rpm, 14.7psi, 97&#37; VE =
((191*5000))/(3456) * 2.0 * 0.97 = ~536cfm of air.

Now let's say we do this your way. I'm putting just under 6.0L of air into a 3.0L motor. So 197% VE. ((191*5000))/(3456) * 2.0 * 1.97 = ~1089cfm of air.

So which is it?

Your solution is the correct one (assuming a few things like 100% IC efficiency and 0 pressure drop), but the equation is a little off. It's not pressure ratio you want, it's density. Your can reduce the pressure if you cool the air, but the airflow requirement is still higher.

Turbocharger exhaust gases. Yes, they are hotter. Also, there are less moles of gas. Less pressure there. When you talk heat, you are talking pressure. Pressure is not what you are worried about when spooling your turbo, exhaust velocity is. Period.

Well, you are still worried about the pressure, for the sake of reversion and the differential across the turbine, but for the purposes of getting it up to speed, not so much as it's obviously going to be fairly low at the point anyway, velocity is what matters at this point.

The standard 4 stroke engine goes through 720 degrees of crankshaft rotation, to complete one cycle. During those 720 degrees of rotation, the camshaft is only open for (generally) 200-240 degrees. The air spends most of its time, sitting there, held back by the intake valve.

That's true for the air at the back of the valve, air in the runner/port and plenum are constantly in motion.

How do we overcome the air's natural tendency to sit on its ass? Well, when the intake valve slams shut, yes, the inertia of the air tries to keep it moving. It slams into the back of the valve, and forms a pulse wave that flows back up the intake runner. Once it hits the plenum, most of the compressed air wave dissipates, but some of it actually reflects back toward the valve. You actually get between 1-4 orders of harmonics going in this whole process (I'm dumbing it down significantly here) depending on length of intake runner.

^Right on the money. But air wave? :sarcasm:

You can't look at cam timing by itself, it's only part of the equation that makes the motor work as a system

Exactly

I've often wondered what effects the custom FFIM's are doing to the harmonics on this motor, and if it really makes any difference in low engine speed power and tourqe. We know the short runner v/s longer runner manifolds do change low end v/s high end numbers. I'm sure the cams and any degree changes or adjustments will also affect this stuff.

Well, once you are under boost equalized distribution is far more important, because of the pressure differential in the plenum vs. runners/ports. Long runners tend to run out of gas so to speak up top because when the velocity gets high enough, you break the boundry layer and the air hits the port roof, causing a tumbling, which mucks everything up. I'm actually pretty surprised noone offers a dual plenum manifold (that I have seen, haven't looked that hard as my MKIII isn't my turbocharged car). That is THE way to go if you want a "good" turbo manifold, unless you have ITBs.

(I'm also more then just a little tipsy at the moment, so I'll look this over in the morning again if I remember)

 

[Doward]

heh, caught that on the PR - I generally use PR as a quick and dirty 'ballpark' figure (especially since the weather will be different on any two days ) Besides, to determine the actual pressure ratio, you have to know the density of the air as well.

And correct as well, at the simplified equation holding many things constant. Pressure drop across the IC, vacuum between the filter and turbo, and IC efficiency all play parts in the process.

Dammit, yes, air wave! Just simpler to think of it that way - it's actually a compression wave, but I was trying to dumb it down (and may have gone too far)

Adjuster - your VE is over 100&#37;, most likely. I'm too damn tired tonight to do the calcs, so I'll just wing it.

I'm going to run stock intake, stock cams, 18psi. I want to see what my torque curve is (and plot my VE to see where the cams run out - current dynos I've seen, show around 5200, then a sharp drop) so I'm thinking I want some 212-216 @ .050" cams, with about .375-.400" lift. I'll design an ITB manifold from there, to maximize harmonics @ 5500-6000 rpm.

just to stress this point, the engine is a system - changing any one thing affects everything!