[DeTomaso] 351 C Compression Question

[JDeRyke at aol.com]

In a message dated 12/8/08 6:54:25 AM, tborcich at msn.com writes:

> My 72 351C (low compression open chamber heads) was rebuilt with TRW Forged 
> flat top pistons.
> 
OEM cast pistons were also flat tops in my '72. The large open chambers 
dropped the compression from 10-1/2:1 to around 8-1/2:1, and additionally, the cam 
timing was backed off by retarding the crank chain sprocket. You really need 
to check the compression volume to see what you wound up with after 
block-decking (and maybe boring? You didn't say), but I doubt if its above 9:1. And thats 
about all those open combustion chambers will stand without pinging on todays 
gas. Closed-chamber heads had 2 large squish areas that vastly increased 
turbulence during the power stroke compared to open chambers, so even with domed 
pistons to fill up the space in your open heads, the useable power will be 
notably less. Expect a hp increase of 35-40 horses just from closed chamber heads, 
which also need less ignition advance. I'd continue looking for new heads- 
ideally, aluminum ones- which with your excellent pistons, will give around 
10-1/2:1 as a bolt-on, and will work fine with todays fuel. I've been running SVO 
heads with flat-top TRWs since 1990 and thats what my measured C.R came out to 
be. Good luck, Tom- J Deryke


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