Offenhauser Heads

P

paleot

Senior Member
I just bought a set of offy heads stamped 375 anyone have any Idea what the compression ratio may be?
Tony
 
The heads have 57 cc combustion chambers. Used on a stock 239 w/no relief the CR will be ~8.41:1, with a relief ~8.09:1. The CR will increase as the bore size increases. In a 255 (Merc) you're looking at ~8.90:1 with no relief, and ~8.56:1 with a relief. The reliefs quoted above would be .0100" and gaskets above would be at 0.057" thick. John
 
Best to measure them, the casting can be all over the place. The 375was for Valve lift, but this didn't clear the Max #1 in most cases with out some clearancing.
 
Thanks John and Ol' Ron info will be a big help. Ron I am planning on running a Winfeild ¾ Cam do you think I will have valve clearance problems?
 
That's impossable to answer. Depending on the net lift and if the heads have ever been milled. are they new or used.
 
Used, but they don't look to be milled at all. I will fit up a couple of valves and guides and check my clearance what is safe?
 
.050" over pistons and the valves should clear, for a street engine the valve clearance isn't that important. the closer the higher the CR
 
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