**** 360 Piston Options ****

nm9stheham said
Re-check your WH405CP CR; the top is a dish, not a dome, so the dish volume should be added, not subtracted. The CR should be only fractionally different from the 405CP, if at all. The W stands for 'individual' (not a set)and the H stand for hypereutectic, and the C stand for coated skirt, but they are the same pistons. Both should work out to around 7.6:1 SCR, not 7.0:1, with 69 cc combustion chambers and .051" head gaskets (the number I used for standard Felpro's).

http://www.fme-cat.com/digipubZ/sealed-power-vintage/#?page=402

I hope you will forgive me for saying so, but one problem with the above calcs is that you are modifying from your original CR number of 7.5 based in the assumption that the old pistons were flat topped. Is that known to be the case? (I am assuming they are not...) Plus you are starting from a number derived from a static compression measurement. That compression measurement is limited in accuracy and in its translation to SCR. It is more accurate to work with straight computations.

I used the data provided in the postings for deck height and piston dome volume. A positive dome is sticking up and taking away volume, a negative dome is a relief and adding more.

The way that I interpret the listings is that they specify the piston deck height, and then you adjust for the dome...

My old pistons were flat top with a dish that I measured the volume above the piston myself to be 34 cc, then backed it into my compression calculations to target a flat top piston. Unfortunately, they don't give the piston specs that way and you have to cross reference the compression height with the dome volume to see how it will affect the new engine....

I'm trying to make an educated guess with the information that is provided to get my engine in the ball park where it needs to be...

I just measured a 340 recently that was supposed to have 10.5 compression pistons that came out to 8.11.... You need to take the stack ups for block deck height and cylinder head volume into account, which is what my process does...