Originally Posted by cdminter59
All right let's do a review on your block and parts. Let's start with the block. Suppose you were to install the crank and a piston at all four corners to calculate piston to deck height. The factory block height of a SBC is 9.025. Most likely you will end up with different measurement on each corner anywhere from .020-.025. To find the deck height you measure from the centerline of the crank to the top of the deck. To find out if the rotating assembly will fit into the block you measure (half the crank stroke - rod length - compression height) = parts stack height. Using yours for an example 1.875 + 6.0 + 1.425 = 9.300. This means the pistons will be .005 above the deck. This would take a .051 thick head gasket for a quench of .046. Your static compression would be 10.492 and the DCR 8.437. Be sure to use modeling clay to check valve to piston clearance. Using 5.7 rods, 1.875 + 5.7 + 1.425 = 9.000. This means the pistons will be below the deck .025. Say you want to use a .027 thick head gasket which cost around $100 each. For me it's easier to mill the deck to .005 and use a stock .039 thick head gasket with a bore of 4.166. You would have a static compression ratio of 10.492 and a DCR of 8.472 which will run on 93 octane gas with the correct timing. With the quench close like this there is less chance of detonation. BTW the 400 engine is not designed for high rpms. Your camshaft has an operating rpm range of 1800-6000. The crank probably has a safe rpm range of 6000-6500 rpms. Rpms is what kills engines not horsepower.
Okay im confused now, firstly if the deck height is 9.025" and with 6" rods the stack height is 9.300" then the piston would be .275" out of the block....and secondly i thought that no matter what rod you use, that doesnt change compression....