johnH20
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| posted on 5/12/10 at 04:49 PM |
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Can anyone explain this?
Just been reading a back issue of CKC mag about their Riot build. Concerning their use of an Omex 600 to manage the 1.7 Puma (VVT ) engine it is
stated that best power is achieved with full cam advance between 1500 and 5100 rpm but peak power at approx 6300 rpm is achieved with zero cam
advance. Can anyone explain the gas dynamics of this? Alternatively anyone with an aftermarket ECU and a Puma engine able to corroborate this claim?
It seems to fly in the face of Honda, Toyota and Rover experience ( different systems I know ) ie. more overlap at higher engine speeds. For the
record max cam advance on the Puma is 40 deg. and cam timing ( without advance ) is inlet 0 - 68 (ABDC) and exhaust 52 (BBDC) 8 (ATDC).
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MikeRJ
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| posted on 5/12/10 at 05:13 PM |
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Advancing an inlet cam almost always tips the torque curve down, giving better lower end torque and less torque at higher RPM.
In terms of gas flow; at high engine speeds the inertia of the gas (plus any pulse tuning) means the gas will continue to flow into the cylinder for
quite some time after BDC. By advancing the cam you make it open and close sooner in the induction stroke, giving less time after BDC for any extra
air to enter the cylinder. Retarding the cam makes it close later, allowing you to take advantage of higher gas speeds.
[Edited on 5/12/10 by MikeRJ]
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