Made an "un-popular" decision with my 307!

[Warrens69GMC]

Originally Posted by rcbildr

Wouldn't the 305 heads hurt performance? I've heard they don't flow very well...or are you going to give them a port job too?

The 307's of the 68-70's got the 185 heads and I belive they were equipped with 1.72"I and 1.5"E valves.

The 305 heads from the 80-86 HO motors (416 casting) had 1.84"I and 1.5"E valves.

On a rebuild using the flattop piston that will yield 8.7:1 with 64cc piston (.04 compressed gasket, -.02 in the bore) you can achieve ~9.4:1 with its 58cc chamber and choosing a head gasket with a ~.030 thickness.

Both of those items will help the 307.