350 frame motor mounts SB VS BB

[aotte1]

1986, C10 with 350 engine and LY6 transmission. Any issues caused by using big block frame mounts? Reason is to raise headers away from ground other then raising the CG of the truck.
Thanks,
Les

[kwmech]

The frame mounts are the same in sb or bb. You may be thinking of the shell that bolts to the block, some of those were a different height. You could also put a factory (found in the wrecking yards) 1/4'' thick shim between the cup and the block

[aotte1]

KW,

I am not very knowledgeable about these trucks, but thought the engine support that goes between the frame and the bolt-in front cross member were different from SB to BB. I think I have two different types of these. The SB ones have a bigger drop, then the ones I think are for BB. Will post pictures of them.

The shim you are referring to, is it similar to the ones used on the 292 straight six on mid 60s trucks? They are cylinders with very thick walls, about 1/2 inch shim.
Thanks,
Les

[Captainfab]

The only difference in the frame brackets for the '73+ trucks that I am aware of is the difference between the C10 brackets and the C20/30 brackets. The C10 frames are taller, so those brackets are taller .

[aotte1]

Captain fab,
Parts books confirms your knowledge for brackets (group 0.029)( this is the bracket that goes from the frame to crossmember), it also shows the next part the "clamshell" to be different for SB and BB (group 0.927) 5.7 is 459021 and 454 is 35717. The next bracket that connects to the engine is different too ( group 0.029) 5.7 is 334601 and 454 is 14067103.

Question if I want to raise engine up in frame ( raise header further from ground) can I use different parts mentioned above. For example the 3/4, 1 ton frame crossmember bracket along with the 454 clamshell and engine bracket?

Thanks for your help,
Les

[aotte1]

Follow-up, continuation of above post, went and looked at my three sets of frame to crossmember brackets and they are all the 361/362 brackets. Two sets were purchased as BB brackets. Picture of bracket purchased as BB below. Then only clam shell is different or they are not BB ???

[aotte1]

Picture for above post

[aotte1]

Another picture

[aotte1]

Another picture of frame - crossmember bracket.

[aotte1]

Number on bracket

[aotte1]

The following are pictures of my original ( 4.3) and what I was told was a BB. The one on the left is the one from 4.3.

[aotte1]

Another picture of them from top.

[aotte1]

This picture shows the different bolt locations for the side with a single bolt. This may be because the BB is longer, therefor, it could need position to attach to the same place on the frame crossmember.

The 4.3 bolted in the center hole of its mount , where as, the reported BB mount bolted in an end hole.

[aotte1]

The one thing I do not have is the bracket that mounts to the block of a BB and via a bolt connects the engine to the frame mount. The size and location of the
bolt hole on this engine bracket may be another place where the BB engine is raised higher from the frame to make room for the exhaust manifolds which are bigger.

Hope this makes sense. I am still researching to see if BB engine mounting parts can be used to make SB sit higher from the ground.
Les

[eric8]

The following applies to 73-87 2wd C10 research that I have done. I wanted to pass this on for the sake of all people using the search function in the future.

There seems to be some misleading info being passed around when it comes to big block/small block interchangeability. Yes, the part everyone gets correct is that you can drop a big block in an original small block equipped truck, using all the small block truck’s original engine mounts, brackets, etc., and it will sit in place.

However, there ARE clear differences in mounting between the two platforms according to GM’s parts catalog.

First, some clarification on terminology. In the photo below, GM refers to item # 1 as the “bracket, frame” item #2 as the “Bracket, engine.” Item #3 is referred to as a “mount assembly, engine.”

Item #1, the frame side bracket, is identical between small and big block equipped 2wd trucks. Item #’s 2 and 3, however, have completely different part numbers for small and big blocks. I am unsure how much difference having “correct” big block brackets and mounts make (in the grand scheme of things) if you’re swapping a big block into your original small block truck. I’m sure it probably shifts the engine up slightly, gives you better fuel pump to frame clearance, big block header/manifold clearance, and would better center your cooling fan if you went all out and got a big block radiator, shroud, and fan.

I am also going to assume the big block specific engine mount assembly (#2) has stronger/thicker/more durable rubber to handle the added torque loads of a big block versus its small block mount counterpart.

I have yet do do this swap, but plan to in the future and this is what I’ve learned, so take that for whatever it’s worth!

[verdell]

Originally Posted by eric8

The following applies to 73-87 2wd C10 research that I have done. I wanted to pass this on for the sake of all people using the search function in the future.

There seems to be some misleading info being passed around when it comes to big block/small block interchangeability. Yes, the part everyone gets correct is that you can drop a big block in an original small block equipped truck, using all the small block truck’s original engine mounts, brackets, etc., and it will sit in place.

However, there ARE clear differences in mounting between the two platforms according to GM’s parts catalog.

First, some clarification on terminology. In the photo below, GM refers to item # 1 as the “bracket, frame” item #2 as the “Bracket, engine.” Item #3 is referred to as a “mount assembly, engine.”

Item #1, the frame side bracket, is identical between small and big block equipped 2wd trucks. Item #’s 2 and 3, however, have completely different part numbers for small and big blocks. I am unsure how much difference having “correct” big block brackets and mounts make (in the grand scheme of things) if you’re swapping a big block into your original small block truck. I’m sure it probably shifts the engine up slightly, gives you better fuel pump to frame clearance, big block header/manifold clearance, and would better center your cooling fan if you went all out and got a big block radiator, shroud, and fan.

I am also going to assume the big block specific engine mount assembly (#2) has stronger/thicker/more durable rubber to handle the added torque loads of a big block versus its small block mount counterpart.

I have yet do do this swap, but plan to in the future and this is what I’ve learned, so take that for whatever it’s worth!

Interesting. I've pulled both 73-87 3/4 ton and 1/2 ton "bracket frames" from the scrap yard and compared them side by side and did in fact see a difference. One of the trucks was an 8 lug and the other a 5 lug but neither had an engine. I'm planning a 5.3/4L60e swap into a '66 and decided to go with the 3/4 ton "bracket frames" as they seem to fit almost perfect (shorter than the 1/2 ton bracket).

[eric8]

Originally Posted by verdell

Interesting. I've pulled both 73-87 3/4 ton and 1/2 ton "bracket frames" from the scrap yard and compared them side by side and did in fact see a difference. One of the trucks was an 8 lug and the other a 5 lug but neither had an engine. I'm planning a 5.3/4L60e swap into a '66 and decided to go with the 3/4 ton "bracket frames" as they seem to fit almost perfect (shorter than the 1/2 ton bracket).

There may be differences between the frame brackets (or “stands” as some call them) between C10 and C20/30 series trucks. I was just saying the frame brackets were the same between big and small block equipped C10 series trucks.