I know off the bat that this is a difficult question. I know quench, piston shape, deck height, etc has a huge effect on the combustion chamber.

However, it seems that there is a significant connection between the efficient combustion chamber design of, say, vortecs, and a good BSFC number -- to the old bathtub design combustion chambers of smog heads and a bad BSFC number.

In addition, the careful construction of an engine contributes as well. Winston cup engines probably get amazingly constructed engines and probably get incredible BSFC numbers. How about us regular folk?

That said, what heads most effectively contribute to a good BSFC number. Ive read good things about the vortecs. Ive heard good things about most 'kidney' design combustion chambers.

So far, the best numbers ive seen from a repudable street engine build was from some AFR 180 heads and BSFC numbers close to .42

What do you think?

 

I don't know for sure, but I'm following this thread to find out, when someone does know.
If I were to guess, it would be some heads similar to vortecs, or as you mentioned the AFR 180s.