I'm trying to determine how much to mill 862 5.3L heads on a stock LM7 5.3 and every compression calculator i use gives me different off the wall ratios I would like to be around 10.1 compression to 10.5 here are the specs i been typing in

Bore 3.779 / stroke 3.622 / .054 head gasket / Deck Height .008 / -8cc piston dome

 

Here are the things Im running into when reading what you typed out. I am assuming, which I hate to do, that your deck height is representing the piston being .008" above the deck, and you have a -8cc "dished" piston. Dome in my mind is the exact opposite of a dish.

But with calculating things as I have assumed them, you would likely need to mill roughly .0325" to get the chambers small enough to get the compression to around 10.1:1. OR you could mill .020" and run a .040" gasket as opposed to the .054 and get about 10.2:1. OR drop in a set of 4.8 flat top pistons with .051-.054 head gaskets and no milling to the heads and be at about 10.5:1.

This was figured using the Cam Motion calculator.

 

Forgot to add, what cam will you be running in this motor? Id strongly suggest measuring your PTV clearance before final assembly to make sure you havent gotten things too close for comfort on the valves.

 

Ill be running a TSP 216/220 low lift cam has .550/.550 lift

 

This is the compression I get when I just type in all OEM specs with factory cc chamber

 

.054 on the head gasket thickness will fix that

Otherwise, thats one hell of a head to block spacer you've got at over half an inch, haha.

But back to business, since the cam you will be running should be nowhere near having PTV issues (Id still measure, just to be safe) Id go with option 2 if you want to mill the heads and run a thinner compressed gasket (just so the chambers dont end up even smaller) or option 3 and get a set of 4.8 pistons and new rings and dont mess with milling the heads at all.

 

Thank you i figured it would be something stupid like that

 

No problem man. Ive done the same thing myself many times