compression test question

nm9stheham said
125-135 psi is NORMAL for a stock 225 /6 motor in very good condition. I got 130 psi +/- on all cylinders with a solid, fresh rebuild with fresh bores, pistons, and moly top rings, the head shaved a bit, and a very mild cam. The compression ratio is just not there for higher numbers in a stockish /6. And yes, the throttle being open vs closed makes about a 5 psi difference on a /6.

Acceptable leak down %? I gotta laugh about this one. 4 cylinder piston aircraft engines are allowed far,far more leakage than is being cited here when cold! Something like 30%!

Air cooled?That would be a whole nuther story.
But,even if liquid, those engines have much different operating parameters.
Our land engines have it pretty easy. They operate over a very narrow temp,and barometric pressure, window. The timing and fueling can be optimized over that window fairly easily. I've never worked on aircraft, but I have heard that they operate over a very narrow rpm band, but with widely varying air pressure and density.Plus IIRC they run a completely different fuel formulation. I have to wonder how that figures into their design.