the difference is in the head.

 

I agree with lsVtec, but its also the computer...b18a1 is obd-0 and b18b1 is obd1...

 

the heads are the same, the casting is the same. ive heard some of the 90-91 b8as MAY be slightly smaller, but no one is for sure. I know the 93 i had was the same as a b18b head. THe intake manifold and exhaust manifold are the main differences, the block is essentially the same. THe valve covers are different from 96+

 

There is pretty much no difference in the 92-93 B18a1 to the B18b. But in the 90-91 b18a the cams are different

 

oh yea those too.

 

i believe the b18b has a little more torque