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Discussion Starter · #1 ·
Puting GT40 heads which i guess are 65cc PLEase correct me if im wrong on that...on a stock 68 302 bottom end drop my CR more than a point??? if so how much anyone know?
 

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You might have to do a little investigation on this one. What were the heads that you took off? Do you know the cc's on those? You might get in the ball park by talking to a local engine builder, and give him the details of what your doing. If you were changing from 58cc's to 65cc's, keeping the same head gaskets, yes, you will lose some compression. You might be able to get a little back by a thinner gasket, but that can cause a few other problems. If you haven't bought the heads yet, maybe another alternative is possible. You're gonna spend some $ on the GT40 heads anyway. Have you looked into a set of Dart Windsor Jr heads? 58cc, already manufactured with 40% larger ports, screw in studs, 1.94/1.60 valves, 3 angle valve job, bolt right on, no special headers needed. You have the best of both worlds then. And you don't have to worry about lowering the comp ratio. I picked my Darts up for $850 complete here in Cincinnati from my engine builder. I think you'll have about the same in GT40's complete with the same type work.
 

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showstang said:
If you were changing from 58cc's to 65cc's, keeping the same head gaskets, yes, you will lose some compression.
That would be 302 GT head (which is the only true 4V Windsor head), all the other were 63cc. If latter, it wouldn't be that radical drop in CR.
 

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Discussion Starter · #4 ·
Im going from the 4b 302 head from 68...53.5CC combustion chamber to something like 64-65 cc.

Is that gonna kill me?
 

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10 cc's is a good sized drop. Still would be best to discuss with an engine builder. But, you could some back with thinner gaskets or milling the heads slightly to clean them up.
 
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