How much head milling = how much more compression?

[92b]

No, only if it's a known combo in identical condition sealing-wise, with no other changes....just chamber volume...if You knew the measured ratio before, You could then calculate the new one based on that. But again, even the method/conditions have to be identical,.....ambient temp, eng temp, battery level/cranking speed, throttle position, number of compression pulse count per test, oil pressure while cranking....bleed down rate diffs in hydraulic lifters will make identical packages register different...sometimes dramatically different.
The upshot is, there are only 2 ways to definitivly check it w/o disassembly, & unless somebody is feeling really generous with their time &/or equipment....it's costly.
The OP is planning on disassembly to improve on it anyways, all the lazy costly ways are pointless here.

I agree with this post except " Lazy, costly and pointless" unless I am misunderstanding you.

 

[slantsixdan]

What part of "you're going to have to measure" do you not understand? We cannot tell you what your compression will be because we don't know what it is now. And you cannot use 8.4 as a starting point, because that ain't what it is either. […] YOU NEED TO MEASURE what you have now and CALCULATE what the difference will be after the .100" cut. There is no magic wand to wave to tell you the answers WITHOUT MEASURING. No matter how many times you ask the same question differently the answer is YOU HAVE TO MEASURE.

⬆︎That's the answer the OP needs. Maybe not the one they want, but that's a different question.