SBC vs BBC motor mounts

[Tiger Joe]

ok I've read on here before that something with the mounts is different on a small block vs big block truck.

We are converting on 79 C-30 from a factory 350 to a 454. So of course I have everything off the small block, since it was in the truck. I also have the following of the 454, which was in a 1978 c-30:

- Clamshells on motor
- frame stands
- motor mounts.

So which is specific to the big block?

[100%Chevy]

If I remember correctly,it's the frame stands.
Been a while for me!
I did this to my 82 in 1990!
Mike.

[b454rat]

Nothing. The rubber mounts are stiffer but small block will work. I've swapped many small to big and didn't change a thing.....the difference is between car and truck, the clam shells are different.

[KrazyRay]

I just pulled mounts from an 85 3/4 ton big block. The frame stands have a slightly different profile then the small block ones. I also pulled mounts from an 87 1 ton with a big block and they are identical to the 85 3/4 ton big block ones.

[Mr.Chevy4x4]

There's some information on the differences in this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=712655

In most cases you won't run into any problems unless you are trying to run something that is already a tight fit....like Hooker 2455 headers. In this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=713218


Mike

[cheepin]

I swapped a 454 in place of a stock 400 in a 79 1/2ton suburban. The only issue was I had to use a shorter fuel pump then the stock 454 truck pump. IIRC it was for a 70 monte carlo with 454.

[Tiger Joe]

so that's 2 votes for frame stands, 1 for clamshells, and 2 for nothing.

no wonder this is so confusing.

I thought I remember reading somewhere that whatever BBC part you need makes the engine site approx. 1" higher than if you had used SBC mounts

[cochino12]

Originally Posted by b454rat

Nothing. The rubber mounts are stiffer but small block will work. I've swapped many small to big and didn't change a thing......

This

[KrazyRay]

There are many different profile clam shells. There are taller clams for some big blocks than others. I know because I used Suburban big block clams in a truck and it smashed the fuel pump on the 454. GM made the clams specific for both the engine AND the chassis it was going in. That being said, it is rare that any clam won't get the job done. Use all of your 1978 parts and you will be fine.

[walkerb]

Yes they are different. I believe the BBC raises the engine up alittle

[Tash4]

the rubber mounts on the frame are the same and are interchangeable. the metal mounts on engine will work both ways but are taller on one than the other.

[MikeB]

I found this info at GMPartsWiki.com:

79 C10,20,30 BRACKET, ENGINE MT. (aka clamshells) for small block is P/N 334601. For a 454, the P/N is 334605.

Frame brackets appear to the same for small block and big block in C30 truck.

http://www.gmpartswiki.com/getpage?pageid=59067

[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.