396 402
 

what is the actual difference in the two motors?

.030 over bore in the cylinders, GM did this with a few blks in the late 70's which were out of tolerance for the 396" bore.

Zip.

so can a guy order a rebuild kit for a 396 just 30 over rings? mains a nd rod journals are the same

396 402
 

In 1970 GM had several 400 inch engines. The 396 was bored .030" to be compatible with the sister divisions 400 engines. I had a new 1970 Nova SS 400/402 BBC 375 horse 4 speed in the fall of 1969. I remember when shopping for engine parts at the Chevy dealer this always came up as a question of the difference between the 400 SBC and the 400 BBC.

Anyway, a 402 uses 396 +.030" parts as its standard parts. If you are rebuilding and increasing a 402 +.030" then it is a 396 +.060 listing that you would use.

There are people in Super Stock that are taking 454 blocks and sleeving them down to 396 +.090" over bore to use as a 402 +.060 legally. In fact there is one listed on RJ now like that. I also have a relative who races a 1970 Chevelle SS with that combo too in a NHRA class.