BB vs SB motor mounts

by 74Malibu383 Thu Aug 07, 2014 12:22 pm

All - Is there a difference between the small block and big block engine to frame brackets?

by 1973 454 MONTE Thu Aug 07, 2014 12:59 pm

i think the frame brackets are the same.
but the clam shell might be different.

back in the day i went to put a 350 in my monte with the 454 clams.it would not fit into the proper location. some people tell me i was nuts,but trust me they would not work. i had to put 350 clams on it,and it set right in.

by 74Malibu383 Thu Aug 07, 2014 1:11 pm

Thanks Chris. Anyone else have experience installing a BB?

by Oldschool454 Thu Aug 07, 2014 1:19 pm

My car was originally a sb, swapped to a bb. The mounts that bolt to the block are the same I remember. The mounts that bolt to the frame are different though. I just looked them up on my parts computer at work and they have diff part #s. The BB lists a 31-9192 and the SB lists a 31-2361. That's a CarQuest part number and I looked it up for 73 chevelle btw. Hope that helps. They also bolt to the frame in different holes but I'm sure you knew that. lol

by 74Malibu383 Thu Aug 07, 2014 2:01 pm

Thanks! Found this on Summit.
http://www.summitracing.com/parts/ani-2395/applications/make/chevrolet/model/chevelle?prefilter=1

Sure does look similar to the Small Block ones I already have.

by bracketchev1221 Thu Aug 07, 2014 2:13 pm

Generally just keep the clamshell and frame mounts together. If you had 350 frame mounts use the 350 clamshells and it will go together.

by Oldschool454 Thu Aug 07, 2014 2:37 pm

Let me go pull some off the shelf and take a look at them side by side....

by 74Malibu383 Thu Aug 07, 2014 2:44 pm

I'm slightly confused with some of the responses. Maybe it's just me...

I've always thought of the "clamshell" as the shell that actually holds the rubber/polyurethane insert, which bolts to the frame.

There is also the bracket that bolts to the engine.

With that said, I am gathering that the engine bracket is the same from SB to BB, but the clamshell is different????

by Oldschool454 Thu Aug 07, 2014 2:50 pm

I wish I could put up pics from work but unfortunately I can't. I put them side by side and they're remarkably similar. I even thought they were same before putting side by side. But they are different. If you put them back to back the mounting holes are about 1/3 onch taller on just one side. The other side matches up though. And height wise, the BB one is slightly taller too. The rubber inside looks beefier on the BB one too and the hole through the rubber for the bolt is bigger. They're common parts. If you're still in doubt you could always just go to your local parts store and compare them for yourself side by side. Most places should stock them.

by Oldschool454 Thu Aug 07, 2014 2:53 pm

74Malibu383 wrote:I'm slightly confused with some of the responses. Maybe it's just me...

I've always thought of the "clamshell" as the shell that actually holds the rubber/polyurethane insert, which bolts to the frame.

There is also the bracket that bolts to the engine.

With that said, I am gathering that the engine bracket is the same from SB to BB, but the clamshell is different????

Yes, to answer that. That is what I'm under the impression of as well. I'm still young and learning so I had actually never heard of it called a clam shell before now. lol, but I googled "clam shell mount" just to be sure which mount you guys were talking about and the one with the rubber came up mostly. But yes, I remember for sure I'm using the same mount for the block that was on my SB. So I'm sure those are the same. But when I did mine I just bought new mounts that go to the frame with the rubber. So I never really campared to my old 530 ones until now. But yes, they are different...slightly

by 74Malibu383 Thu Aug 07, 2014 2:53 pm

That's awesome. Thank you so much for the help on the clamshells. Can you tell if the 2 "rods" that flank the hole through the center look like they have the same dimensions? IE - distance/pitch? If so, that might verify the bracket that bolts to the engine is in fact the same.

by Oldschool454 Thu Aug 07, 2014 3:08 pm

The length for the bolt will be the same since the SB/BB mounts to the block are the same. Plus I just measured the 2 different mounts to be sure. As far as bolt diameter, I would assume you need a slightly thicker bolt. I know on my car I used the same bolts as the SB but I probably needed to get different ones. lol I measured the diameter of the hole in the rubber the bolt goes through on both mounts, and the SB hole is 1/2 in. The BB hole is 1/8 in. larger (5/8ths right?). Hope that helps. I would get different bolts.

by Oldschool454 Thu Aug 07, 2014 3:11 pm

Sorry, I misunderstood what you were saying in your last post. lol But yeah, because since the length of the rubber from end to end where the bolt goes through on the SB and BB mounts are the same I have to asssume those brackets are in fact interchangeable for sb/bb. Only difference for the bolts that I can see would be diameter like I was saying.

by 74Malibu383 Mon Aug 11, 2014 2:31 pm

How about BB Headers?
What are you running?
How was the fit?
Do you have any photos?

by Oldschool454 Mon Aug 11, 2014 2:47 pm

I have pics I can post later tonight. (at work now) I just have hedman shorty headers. That's another problem I heard of if you find a way to make sb mounts work since they're shorter you will have clearance issues with headers. I'll find the link for the headers I have and post it. with my headers I have 1/8 in or so between pass side header and the frame so it's already a tight fit. And on the drivers side had to make a veeeery small "ding" in 1 of the tubes so it wouldn't rub on frame. But nothing too bad. They fit well.

by Oldschool454 Mon Aug 11, 2014 2:48 pm

http://www.summitracing.com/parts/hed-68610?seid=srese1&gclid=CK6e7-zvi8ACFQwEaQod20cAeA this is what I have.

by Oldschool454 Mon Aug 11, 2014 2:50 pm

My car is pretty low up front too so this is just about the only header I could use. I like them. Just wish I had ceramic coated to help keep some of the heat in the tubes.

by Oldschool454 Mon Aug 11, 2014 9:42 pm

This is the closest pic I could find until I can go out and take some closer pics, if you want. It's a snug fit.

by Oldschool454 Mon Aug 11, 2014 9:44 pm

I can bet that if I had used small block mounts no header would have fit.

by Fishgrinder Tue Aug 12, 2014 7:44 am

Hmm.. I also thought the frame mounts were the same between small block and bigblock. There is a difference between the
small block and big block engine brackets, if you read the information provided by 1973_454Monte here:

http://www.g3gm.com/t3390p195-1975-monte-carlo

I ended up using small block brackets when I installed my 454, and they landed on the frame mounts just fine. The clearance between passenger side header and frame is marginal though.

by 74Malibu383 Tue Aug 12, 2014 12:05 pm

Thanks for the thread! I see there is a slight difference. So the question now is: Does anyone have any BB engine brackets that are for sale???

by bigredlaguna Wed Aug 13, 2014 12:59 am

So what 3 numbers are you going end your stage name with? Or are you going to keep it 383 for sleeper effect, lol.

by 74Malibu383 Wed Aug 13, 2014 1:16 pm

HA! Thought about that. Not sure I'll change my stage name, but the increase is 189...

by BlackChevelleSS Thu Aug 14, 2014 12:37 am

Big block will drop right in with the sb mounts, Done it multiple times. I was using the Hooker Comp headers 2" primarys and they fit GREAT only issue with them was we had to grind a notch in the clamshells for one of the primary tubes to clear.

by Trbulnc Fri Aug 15, 2014 1:48 pm

There is a small difference as said with frame mounts. BB side sits higher on one side (can't remember which side but I think drivers side) to provide some additional clearance.

Having said that I have installed them both ways without issue on many cars. Haven't ran into a problem yet but that is always hanging out there.

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