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Oversquare Pistons
Posted:
Tue Nov 19, 2013 9:44 amby VtwinFTW
Not sure if this is the right palace to post this.
Whenever I build an engine, making the pistons oversquare hurts performance. The engine doesn't rev any higher, even at extremes (lowest stroke, greatest bore) and I just get hp losses. Am I missing something?
Re: Oversquare Pistons
Posted:
Tue Nov 19, 2013 10:13 amby Der Bayer
The problem you described sounds to me like you are having valve float issues. Does the engine die because of valve float or bottom end problems? If it's valve float, choose better top end parts (more valves) or increase the cam profile. As long as you are not running into valve float, shorter stroke will rev higher than long stroke.
Re: Oversquare Pistons
Posted:
Tue Nov 19, 2013 11:17 amby Daffyflyer
Larger bore also mildly increases head flow, as there is room for bigger valves in the head. Sounds like you might be getting held back by other factors.
Re: Oversquare Pistons
Posted:
Wed Nov 20, 2013 10:16 amby VtwinFTW
5 valves per cylinder DOHC.
Direct Injection
Maxed out cam profile
Racing intake and exhaust
No flow problems here. No valve float warning either.
Shorter stroke SHOULD allow higher revs, due to reduced piston speed. Not sure if the simulation takes that into account though.
Re: Oversquare Pistons
Posted:
Wed Nov 20, 2013 11:41 amby Daffyflyer
VtwinFTW wrote:5 valves per cylinder DOHC.
Direct Injection
Maxed out cam profile
Racing intake and exhaust
No flow problems here. No valve float warning either.
Shorter stroke SHOULD allow higher revs, due to reduced piston speed. Not sure if the simulation takes that into account though.
It only allows higher revs if the limitation you're running into is the strength of the bottom end. If the bottom end is strong enough, then making the stroke shorter won't help any further.