SBC vs BBC motor mounts

[flatbed82]

The rubber mounts are different for a small block and big block on how they bolt to the frame stands, that is the only difference. Both style of engines share the same two upper bolt locations, the lower hole location is what's different. The lower mounting bolt on a small block mount is on the outer edge (off center), the lower mounting bolt for a big block mount is in the center. The spacing of the upper bolts to the lower bolts is also different between the two mounts. You can use either mounts if your frame stands have both sets of holes. As for the clamshells you can use ones that came off of a small block or a big block and have no problems. Look at the back of the clamshell that is towards the block when bolted on to the engine. If the triangle is facing out to the block there needs to be a spacer plate inbetween the clamshell and the block, if the triangle is indent away from the block no spacer is needed. The spacer usually has a support rod hooked to it going to the transmission or transfer case. Using the spacer with the clamshell with the triangle facing out to the block puts the crossbolt at the same heighth as the clamshell with the triangle facing away from the block. that's why one clamshell is shorter than the other, the spacer makes up the difference.

[PowerdbyChevy79]

Originally Posted by flatbed82

The rubber mounts are different for a small block and big block on how they bolt to the frame stands, that is the only difference. Both style of engines share the same two upper bolt locations, the lower hole location is what's different. The lower mounting bolt on a small block mount is on the outer edge (off center), the lower mounting bolt for a big block mount is in the center. The spacing of the upper bolts to the lower bolts is also different between the two mounts. You can use either mounts if your frame stands have both sets of holes. As for the clamshells you can use ones that came off of a small block or a big block and have no problems. Look at the back of the clamshell that is towards the block when bolted on to the engine. If the triangle is facing out to the block there needs to be a spacer plate inbetween the clamshell and the block, if the triangle is indent away from the block no spacer is needed. The spacer usually has a support rod hooked to it going to the transmission or transfer case. Using the spacer with the clamshell with the triangle facing out to the block puts the crossbolt at the same heighth as the clamshell with the triangle facing away from the block. that's why one clamshell is shorter than the other, the spacer makes up the difference.

Great info here.