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Cam timing vs VE vs max power

Variable Cam Control Tuning

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Discussion and questions related to the course Variable Cam Control Tuning

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Just a concept that I am having trouble grasping. Why on the dyno(in the cam tuning course), are we not getting the most power when max VE is achieved? To me I think it would make sense to tune the cam timing based on maximizing VE, which can be done without a dyno using fuel correction factor in closed loop. Then tuning ingition timing for MBT. What are the factors that cause more power to be made at less VE for a specific load and rpm?

Hi Derek,

Max VE typically happens at peak torque, and the VE maps shape should mimic the torque curve of the engine.

As Steven said, TRUE VE is a measure of actual cylinder filling and is normally around peak torque - think of it as the biggest bang.

Whereas power is best thought of as being roughly (there are variables to consider) proportional to the amount of air passing through the engine - think of it as the size of the bangs times how many there are a minute. As RPM rises, we can trade off the poorer cylinder filling (bang) for more of them - see first equation..

It certainly is possible to design the engine to produce maximum torque (biggest bangs) at higher rpm, but this will tend to reduce torque at lower rpm and make the useful rpm range smaller - sometimes referred to as a 'peaky' engine.

The actual equations for the rpm, torque, and power are quite long, but for simplicity we use a constant of 5252 (been a while since I did it long hand, but IIRC, it's actually around 5252.02 - anyone? So close enough!).

They are

P = T x rpm/5252

T = P x 5252/rpm

rpm = P x 5252/T


P = horsepower

T = torque in lb.ft

rpm = engine speed in revolutions per minute.

I think I may have worded my question wrong. I am refering to each individual tuning cell. In the cam timing lesson, Andre is using the dyno to find peak torque for each cell by adjusting cam timing. I am understanding that peak torque should occur at peak VE for each tuning cell. Can I just tune the cam timing for each cell by finding what position gives the highest VE? Shouldnt that give the best end result, before going back and tuning ignition? I feel like I should be able to tune the cam timing without a dyno by finding the cam timing position that requires the most fuel to meet the target A/F. Would that not result in the highest torque(once the rest of the tuning is complete)? If not, why? (I am primarily refering to intake cam timing)


Assuming you are talking about using the ECU’s wideband fuel trim as a SD VE feedback tool then yes, I can’t see any reason why what you are proposing isn’t reasonably accurate and it’s exactly how I have been tweaking cams remotely for clients as a COBB Protuner. I log the fuel trims average over 3 runs in a histogram, tweak the cams then have the client do me another few pills and do the same.

If the fuel trims move more positive at any point in the pull we can safely assume that the engines VE has improved at that point.

it’s an interesting topic to be fair, it’s disappointing that you didn’t have much take up on it.

Assuming complete combustion and no fuel blow through during overlap, more Injection Pulsewidth for the same AFR should be representative of higher VE, I think. But with the way real world engines operate, I don't think how accurate that method would be.

It's very accurate, based on my experience. Do you have a counter example / data other than "based on the way real world engines operate".

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