Quote:
Originally Posted by renault_megane_dci
36 tooth sounds familiar for cams in general.
I might be wrong but I think whatever you do on a motorbike engine is detrimental to top end, since those engine are very optimised.
Delaying the inlet would have the effect of "atkinsoning" the engine though, wich should be good for MPG but bad for high speed.
QUESTION :
Is your goal to vastly improve FE while not affecting top speed ?
OR
Is your goal to reach a given MPG (100 IIRC) and try to get as much speed as possible ?
If you are looking for the second option, the compromise is gonna be trickier I think ...
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I don't think this is true. Anything with fixed cam profiles isn't optimized anywhere because it's a compromise for everything. With phaseable cams you can have 1 optimal operating point (for power), and an optimal "curve" for efficiency. For example the CBR600RR has a 15k+ rev range, peak torque at 11k, peak power at ~13k. BMEP at power peak is actually somewhat poor considering how much overlap is available.
Car engines with close to zero overlap at the top end can achieve higher BMEP at peak power (typically 100Nm/L ish), though car engines don't rev as high so it's a little easier to hit higher BMEP, though if you look at liter bikes the story is still the same. By retarding the intake cam on a bike, the "midrange" (which is like the 7-11k range or something lol) will suffer a bit but the very top end probably gains a little. All in all, a peakier powerband, but possibly more peak power, and less torque down low but better combustion stability from less overlap. At least that's what I think should happen.
Bike engines have so much duration that they're essentially already "Atkinsoned", but there's way too much overlap for good part throttle efficiency.