Hi!

I'm putting together a 440 and was comparing piston height. I have two sets of new flat top cast pistons on rods and was trying to figure out what the compression ratios would be for either set if my 440 had a stock deck and stock 906 heads. I know that MOPAR lowered the pistons in the bore to lower compression back in the 70s and was trying to find a guide on line for piston height over the 70s.

My stock 1968 HP2 440 pistons are .060 taller than one set and .040 taller than the other set of new pistons. I know that the pistons that are .040 lover than stock would be more compression but by how much?

My .060 lower than stock are on reconditioned rods that were balanced with new ARP bolts. THe .040 I bought already attached to the rods but these were not reconditioned at all. Any guess as to what the compression ratio would be with either set? (stock deck and heads)

Maybe I shouldn't use either of these pistons for this stock rebuild?

Thanks for any advise.

Carl

Without actually mocking things up & miking everything you could plug in the nominal specs into http://kb-silvolite.com/calc.php? and see what you get for CR. Nominal for the deck is 10.725" then 1/2 of the stroke, rods are 6.768" and your compression heights then the gasket thickness and the head cc's and get a rough estimate of where you are at. EDIT about the "040 lower set" way back I hung some new pistons wo checking the rod big & they were so out of round that I had to find a shop w the fixture that goes under the rod small end to support it as the pistons were pressed back off. 1st what octane will you be running/how wild (or mild) of cam and what CR are you shooting for? and are you interested in getting quench w the 906's? If so it's KB time plus milling the 906 head recesses to equalize the depth and the slope plus milling the flat quench pads on the appropriate KB pistons but achieving quench is for sure worth it imnho.

I was thinking of a 268 cam like the voodoo 60303. I'm not too worried about having to use 91 octane over 87.

I'll do the other measurements and try the formula, but have had problems in the past trying.

Thanks
Carl