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Originally Posted by bruce.augenstein@comcast.
My position would be that variable cam timing can be used to widen the torque bump due to header tuning, so you can in effect make header tuning work over a wider rpm range.
How does VANOS affect duration? This is new to me.
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I am pretty sure The camshaft phasers in the VANOS system on the newer BMW engines have the ability to adjust the cam while it is on the ramp....... Since the cam is changing position while the valve is open it is affecting duration. This is one of the reasons why cams show relatively small gains on the S65 and S85
Quote:
Originally Posted by bruce.augenstein@comcast.
Seriously? What would rpm have to do with VANOS' "need for speed" to alter cam phasing?
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The VANOS phasers on the S65 have a rate of adjustment of 360 degrees per second. As RPM's climb higher there is less time to adjust the camshafts (since combustion events are happening at a higher rate) therefore you want to tune the intake and exhaust to work best near higher RPM. The reason for this is that you want the amount of cam adjustment required to open the valves at the proper time to meet the resonance wave to be minimal since there is less time to do so.
Quote:
Originally Posted by bruce.augenstein@comcast.
At some other rpm than the resonance range, you just lose the resonance. Second order resonance is miniscule.
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You don't lose the resonance, the valves just open at the wrong times for the resonance wave to have an effect. In an engine with VCT the intake and exhaust valve timing is varied so that the resonance wave is not used at a specific RPM but rather over a wide range of RPM's
Quote:
Originally Posted by bruce.augenstein@comcast.
My perusing of S54 exhaust manifolds shows shorter runners.
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Yeah they sure are shorter........ I was thinking of the primaries on the headers on the S50B30 euro engine like in my 94 Euro M3..... And even they are probably not longer but are close to the same length of the S65. Torque peak on that engine is 236 Lb/Ft at 3600 so not a good example to prove my point anyway.
Quote:
Originally Posted by bruce.augenstein@comcast.
given you my thoughts on the discrepancy between intake and exhaust runner length on the S65, and why this is so. So give me your thoughts on why this is so. You think this is an accident?
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No I am sure there is no accident in the runner length as I am very sure there was extensive R&D and engineering to obtain the final product.
Everything you say is correct and with a proper thought process. My only argument is that I don't think that the header design is the single thing that moves the torque peak lower on this engine. I feel that the intake and header design was a compromise to get a torque curve that stayed flat almost till redline with the help of a sophisticated variable cam timing system.