[dbiscayne]

Trying to figure out what the compression ratio would be for the following:
1995 351W stroked to 388ci with a 3.85" stroke crank, deck height is 9.5", not bored,
stock length rods at 5.956",
stock Ford forged 302 pistons w/1.605" compression height out of a GT motor but I don't know what the dish volume is,
GT-40P heads w/61cc chambers, stock valves for now,
Cam will be around 0.510 to 0.540 lift max with an overlap around 112 deg.

I'd like to be close to 10:1 or just above, will mill the heads if I have to. If I knew what the piston dish volume was for a stock GT forged 302 piston was I could probably get an answer, heres a good link for figuring the compression:
http://www.torinocobra.com/Randys_tools.htm

 

[ckelly]

Should be around 11.5:1 with the pistons .010 down from the deck using 5cc dish. That's guessing, since you don't have deck info, the dish volume and head gasket data. It'll be 392 CI if it's bored .030. If not it'll be 388 and 11.33:1. 11.22:1 if you used the rod, stroke and pin height and a 9.5 deck - which it almost never is. To get accurate figures you have to mock the engine up.

 

[Is1BadFord]

Aren't factory 302 heads more like -13cc's? I know with one set of valve relief's my custom pistons are -6cc's...and if you double that for four 'eyebrow' valve relief's, and include the dish milled into the center, I'd think quite a bit more than 5cc. I don't know for sure!! Just saying, I think it's a bit more than that.

Anyhow, with a 13cc dish, I'm getting roughly 10.38:1, using a 4.00" bore, 3.85" stroke, 61cc heads, a .039" compressed head gasket, with a 4.1" gasket bore.

Anyhow hope that helps, ckelly's data is also very accurate, if his measurements match your parts better.

Cris

 

[dbiscayne]

Thanks thats the kind of info I'm looking for.
Somewhere I read that the factory 302 pistons with the 4 valve reliefs and a shallow round depression had a dish volume of about 4.6cc's? If that is the case that puts me at about 11:1 with GT-40P heads (62cc comb. chamber's).
With a dish volume of 14cc's that gives me 10:1, that would work too.