CompSyn
Well-Known Member
it has small tube headers. the machine shop that assembled the motor stated 10:1 cr used the .40 replacement head gasket. i ask them to use a .20 shim if needed to get 10cr tomorrow I'll start checking cylinder psi, vacuum leaks again i know I'm just missing something silly appreciate the help
If the shop that built your engine told you 10:1, I'd ask them for the actual measurements they used to arrive at that compression ratio. They'd need to know actual measured CCs of the combustion chambers after machining the heads as well as where the pistons sat in the hole at TDC after cleaning up the block deck.
Using some of the commonly known measurements taken from these production engines; your KB400 piston specs, and the measurements of your compressed head gaskets, your engine is likely 9.0:1 as seen with this Diamond calculator pictured below.
The CompCams #287TH7 calls for 9:1 compression, but the problem I see is that Comp is making the same recommendations on the cam card for both the 383 and 440. That's a significant difference in cubic inches. That said, I still think you're over-cammed with your given combo. Instead of the 287, I'd be looking more towards a 272 or even a 268 for what would be a happier more potent 383.
But really, my next step would be to call and get some recommendations from Bob Karakashian. Bob knows these Mopars really well and can make some suggestions to you.
Last edited: