The SpeedPro Hypers ALMOST NEVER (I would say "never", but that's a very dangerous word to throw around...) have the same compression height as stock. That is, they are "designed to fit" an engine with a nominal compression height of 1.425", which is NOT the same as saying their CH is 1.425".
Nearly all of them add the usual "rebuilder" .020" of deck clearance, since it's alot less of a problem for a rebuilder if the motor comes out with slightly lower than stock compression and works, than it is if they have to deck the block to repair a blown head gasket scour or something, and then the pistons hit the heads.
Note that their compression spec is lower than you get when you put .025" deck clearance into whatever "calculator" you're using. Instead, it matches what you get when you put .045" deck clearance into the calculator. That should be a red flag to you that the CH is NOT 1.425".
Measure with a mic between the top of the pin bore and the top of the piston. From that number, subtract half of the pin diameter of .927", which would be .4635". If the pistons are REALLY 1.425 CH, the measurement will therefore be 1.425" - .4635", or .9615". More likely, the measurement will actually be .9415", indicating the extra .020" of deck clearance, or about .045" "down in the hole" at TDC.
Nearly all of them add the usual "rebuilder" .020" of deck clearance, since it's alot less of a problem for a rebuilder if the motor comes out with slightly lower than stock compression and works, than it is if they have to deck the block to repair a blown head gasket scour or something, and then the pistons hit the heads.
Note that their compression spec is lower than you get when you put .025" deck clearance into whatever "calculator" you're using. Instead, it matches what you get when you put .045" deck clearance into the calculator. That should be a red flag to you that the CH is NOT 1.425".
Measure with a mic between the top of the pin bore and the top of the piston. From that number, subtract half of the pin diameter of .927", which would be .4635". If the pistons are REALLY 1.425 CH, the measurement will therefore be 1.425" - .4635", or .9615". More likely, the measurement will actually be .9415", indicating the extra .020" of deck clearance, or about .045" "down in the hole" at TDC.
