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      09-23-2012, 02:37 PM   #12
BMRLVR
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Drives: 2011 E90 M3,1994 Euro E36 M3/4
Join Date: Apr 2006
Location: Fort McMurray, Alberta, Canada

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Quote:
Originally Posted by Mike Benvo View Post
We're talking velocity stacks here, not cams. There are companies that offer them which produce gains without tuning.

I have tuned cams on the S85 motor with great results, so yes I have full control of the intake and exhaust cams, both warm and cold (within the factory limits of the vanos system). You can only target positions of the cam within a certain range.

I'm not interested in arguing with you,
so let's agree to disagree peacefully. My tuning speaks for itself.

Well Mike, I am not trying to fight or criticize or argue with you so no need to be defensive. I have no doubt in my mind that you have the ability to tune the VANOS system within the limits of the cam phasers and at the maximum rates of adjustment the phasers will allow.

With the above being said, a person tuning needs to have an understanding of what makes power in an engine. The stock intake system in both the S85 and S65 and every other BMW S engine ever made (with the exception of the S50B30US and S50B32US) used velocity stacks inside the air boxes. The cam duration on the intake side is what allows a velocity stack of a specific length to make power at a specific RPM. Changing the length of a velocity stack will change the RPM the torque peak of the engine occurs. Generally, shorter velocity stacks make peak torque at higher RPM and longer velocity stacks will make peak torque at lower RPM according to the effect of (depending which wave you are using in the resonance pulse that occurs). The torque curve of the later S engines (VANOS Engine are the ones I am referring to) was flattened by continuously changing the cam duration to be able to make this resonance effect occur right through the RPM range rather than at a specifically narrow RPM where they would occur without variable cam timing. So velocity stacks and cams have a very close relationship whether you realize it or not. Engine builders of the past would select their port shape, diameter, cam duration and lift and intake runner or velocity stack length in concert with one and other according to where they wanted the engine to make peak power and torque

Although I am not interested in these velocity stacks for my car and the fact that I don't like the design due to the lack of air filters, the statement that they are not the same as cams for tuning is totally false. If you have the ability to adjust the cam angles in the VANOS tables of the ECM there is no reason you could not write a tune for these stacks to make good power with them and possibly even more than the stock plenum/stack configuration. Having the knowledge of engine tuning fundamentals and applying them to make power is a different thing.

P.S. 58 degress of cam timing adjustment on the intake and 48 degrees on the exhaust at a rate of 360 degrees per second, is lots of adjustment to take advantage of almost any stack configuration over the usable rpm range of roughly 7400 RPM.
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Last edited by BMRLVR; 09-23-2012 at 02:46 PM.