[Jay S]

Usually a TRW/Speed Pro replacement OEM piston is .005” shorter than the original OEM cast piston it replaces, cast are usually .015” shorter. Some casts are .020” shorter. I am not sure if .005” is true on the factory forged pistons. Usually can work backwards from factory deck heights and get a decent range estimate for piston to deck height. That seems to apply for all brands. My OEM 71 455 had a piston to deck height of .003”-.004”, compression height measured 1.502” instead of 1.497” TRW/ Speed pros have. Typically a 400 OEM cast pistons I checked are 1.719” instead of 1.714” on a TRW/Speed pro forged. I don’t check them all, but it generally seems to line up with what others are reporting.

I have a 400 that the deck height is .013” taller on one bank versus the other. The taller bank was what you would expect, the shorter side is the anomaly. OEM mfg tolerances are not always as tight as you would expect them to be.