Big Block vs. Small Block frame mounts [Archive] - Chevelle Tech

: Big Block vs. Small Block frame mounts

Jul 5th, 06, 6:25 PM
Can anyone tell me the difference between the motor mounts for a big block and a small block on a 1966 Chevelle? I have a pair of small block frame mounts and what I believe to be a pair of big block motor mounts. However I need to use them on a 454. Someone has told me that "technically" the frame mounts are different for a big block but many people have used the SB ones. Apparently the only difference is that the block will sit a little bit closer to the radiator support if I do use the SB mounts. Is this true? If so, how much further will the motor sit towards the front and will this cause problems when I use the stock driveshaft?

Mr Chevelle
Jul 5th, 06, 7:01 PM
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The frame stands for SB and BB are dimensionally the same except the BB stand has an indentation for the motor mount safety lock feature.

The difference between a SB and BB motor mount is the BB mount has the T-lock or safety lock feature.

The BB frame stand will accommodate both BB and SB motor mounts. The SB frame stand will NOT accommodate BB motor mounts because of the safety lock feature.

The frame stand determines the motor mount regardless of engine displacement.

All Chevrolet V8 engine blocks from 1958 up have the same motor mount boss configuration regardless of displacement.

I hi-jacked the picture below. I can't remember the author of the post but they did an excellent job. The BB frame stands are middle of the top two rows.

Jul 5th, 06, 7:55 PM
Would it be ill advised to cut off the "T" lock to get the BB mounts to work with the SB frame stands?

Jul 6th, 06, 12:56 AM
Would it be ill advised to cut off the "T" lock to get the BB mounts to work with the SB frame stands?


Installing a big block with big block mounts on small block frame stands will result in an engine that sits higher than it would with big block frame stands as well. Some header manufacturers dictate that their BBC headers will only fit if big block frame stands are used so this should tell you something.