AndyG123

Hey all, I was wondering if anybody could confirm or deny this claim. I read somewhere that an Oldsmobile head is an olds head, and that big block heads fit on the small blocks and vise versa. I have a 307 that I want better heads on, it currently has 7a heads, and a set of J heads are around $150. I know j heads are smog heads, but any head at all is better than the 7a heads, right? And keep in mind I'm kind of on a budget here

oldsmobiledave

7a are 1972 SBO heads. 7A are 307 heads.

Either way stop wasting your time with a 307. Replace it with a 330 350 or 403.

83hurstguy

Don't even try it... the BBO chambers are huge, valves may hit the bores... 307 uses a smaller diameter head gasket than even the 350.

I considered 330 heads at one time, but never tried to figure it out for my old '83. I ended up mildly porting the 5A heads with bigger valves, and milled like 0.055" off them... they worked pretty well, the engine just needed more compression and cam.

joe_padavano

To answer the OP's question, yes the BBO and SBO use the same architecture. Bore spacing, head bolt pattern, and intake and exhaust manifold bolt patterns are the same. The problems are the excessive combustion chamber volume (which will drop compression ratio) and much larger posts that will kill what little torque the 307 has. The different head bolt diameter is the least of the problems.