400 magnum compression

[72_rallye]

Does anybody know a formula to figure out my compression on my 72' 400. It has stock replacement pistons but the block has been deck milled off by .060. Heads were milled .010. The heads are 1970 906's, with Felpro blue gaskets.   Thanks,,,,,,Nick

[RD]

how far in the hole are the pistons?  2 bbl version were mostly rated at 8.2 to 1 whereas 4 bbl HP versions had 9 to 1 pistons (i believe, it could be 8.5 to 1 or 9.5 to 1, not too sure on that).  Either way, the only way to accurately determine compression is to (1) CC the head chamber (2) see how far the pistons set in the hole (only if they are flattops, domes require more calculation) and (3) calculate the above in regards to head gasket thickness.

[Nacho-RT74]

8.2:1 in stock 400 4bbl ( magnum 400 ).

I don't thiking by now on milling down my heads but thinking on replace stock gaskets for the metallic ones ( already in my hands ).

definitelly I won't mill down the block, just heads.

[firefighter3931]

The factory rating was 8.2:1 but in reality they were closer to 7.8:1....yours will be better due to the machinework. If there's been .060 removed from the deck....you will have intake manifold alignment problems ; be prepared 

Ron

[72_rallye]

Motor is together with about 15,000 miles on it, Pistons are flatops, don't know how far down they are in the holes. They did mill the head surfaces to match the intake. I just changed cams in it and seen that It had 1970 heads on it.  Thanks for all your input !!!!!!

[Chryco Psycho]

you can use the Speed pro low comp piston for a 440 in a 400 & get a high comp flat top if you are changing pistons