Im starting to change my thinking about EVO and EVC. Not so much as it relates to overlap but more in general terms how EVC and EVO are affected by rod to stroke ratio and the time that the piston spends around TDC and BDC.
To that end, a higher R/S ratio may want an earlier EVO so that when the piston reaches BDC you are at or near atmospheric pressure to reduce pumping losses. Since the piston is moving around BDC quicker (and I’m assuming faster) if you delay EVO you increase the pumping loss.
Which makes me assume (at least at this point) that when the cam is advanced and the power goes up that it is more likely due to the earlier EVO and reduced pumping losses (even though you may and probably do give up some of the expansion) and not so much to the earlier IVC.
And if that’s the case then a high(re) R/S ratio and a late EVO may be hurting power.
Ive always been of the opinion to delay EVO so that you get as much out of the expansion stroke as you can. But now I’m questioning that philosophy.
I also think that header sizing is impacted by this, as the sound/pressure waves would have to be different with different EVO’s.
The more I learn the more I learn I don’t know much.
