Originally Posted by moparx
what would be a "minimum" overlap, or duration at 50, when approaching 11 : 1 static compression ?


It's not that simple: chamber design, piston top design, quench height, camshaft seat duration, LSA... not even all of the variables that can factor into this.

Also, some people say the overlap influences cranking pressure, I've always understood it to be a result of the intake valve closing point. A lot of overlap does impact the ability of the engine to have more complete combustion at lower RPMs That's not cylinder pressure; it's dilution of the air/fuel mixture with residual exhaust gasses.

And, there's been a running debate (about which I've presented my position in the past) of whether the engine build should target cylinder pressure based upon using a "higher" CR and crutching it with a longer-than-normal-duration cam, or targeting a more "typical" CR for the fuel to be used and spec'ing the cam to be aligned with that CR.

I've been through that last topic enough that it's now included in my no-no discussion categories, along with politics, religion, and choice of engine oil.