How far in the hole 318 pistons

James Clews said
Does anyone know how far down a 1972 318 pistons are? In a book I have it states in 1972-1981 they are .056 down from the top of the bore but with those calculations in the Diamond racing compression calculator it gives about 8.5 to one compression but our factory manuals state 8.2 compression ! I tend to think that the pistons are further down in the bore. I would like to find out the real comp before I pull the heads off as I would like to custom order a camshaft but need a more accurate reading on my compression ratio as it may take a few months to get a custom ordered roller cam and I would not like my engine sitting unassembled for many months.

By 72 emissions were kicking in and the CRs dropped into the outhouse basement. Between either dish pistons or 0.040" to 0.100" down and combined with open chamber heads the combustion was terrible and prone to detonation. Best bet would be figure new pistons to zero deck it with modern rings with 1.2mm width. This reduces friction. You want pistons with 2 valve reliefs not 4 and flat top. Also plan on in the future getting heads like the Edelbrock closed chamber for good quench which is high mixture motion. Good for efficient combustion.
Calculate your compression based on that and order a cam, lifters and pushrods to match. You can change the pistons next winter and then the heads the year after that.