mr-tom

i remember reading some were that you can put bbo heads on a sbo any one hear of that too ?

joe_padavano

Unlike Chevy motors, the BBO and SBO use the same architecture (bore spacing, bolt patterns, etc). The main difference is the taller deck height of the BBO to accommodate the longer stroke (plus larger main and rod bearing journals). As a result, yes, big block heads bolt right onto a small block. Whether this is a good idea is a different question.

First, big block heads have 80 cc chambers as compared to the 60-64 cc chambers on small blocks (though later smog motor SBOs do have big-block size chambers). The result is that you need to carefully select pistons and possibly mill the heads to keep a decent compression ratio.

Second is the port size. Big block heads have much larger ports and unless you plan to spin that small block to high RPMs, it isn't clear that this is a benefit. The exception might be a 403, since that engine WILL move enough air to use these ports (as did the big block 400 motors).

Third, the Performer RPM is probably the only intake with enough meat in the casting to allow the mainfold to be ported to match the big block heads. If you don't port the intake, the flow disruption will negate any benefits from the heads.

The big block heads do bring larger valves, but you can easily put these valves in the small block heads, which is what the factory did on the W-31 motors. Everything else about the big block heads bolts right up to the small block (rockers, exhaust manifolds, valve covers). Also, be aware that 76-earlier motors (big and small) use 7/16" head bolts. 77-up motors use 1/2" head bolts. You need to drill out the holes in the early heads to put them on a later block.