Large rpm drop

OK, well I'd expect that if the eyebrow/notch volume is being deduced from the down-fill method, then some of that volume is actually from the crevice volume down by the top of the piston. That usually works out to 1-1.5 cc in the size range of these bores. I add that to the published eyebrow volume (or reduce the net dome-eyebrow volume for a domed piston) to account for that. Pretty much the same end result either way.


It can be but I seal off the top of the piston with grease to eliminate crevice volume. You can calculate that too later on, and it also matters how far out of the bore the piston is, because sticking the piston out of the hole will reduce crevice volume.