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Hey guys,
I did a search and read all the articles on conversion from small block to big block on my '70 chevelle. It's still clear as mud. Some say the same frame stands and motor mounts are used for both. Some say you must use small block mounts for clearance for the '70. Is there a definitive word on this. Will my small block frame stands work with the new big block motor mounts I bought? HELP!

Thanks much!

Tim
 

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I just got done pulling my small block and installing my 454 into my 72 chevelle vert about 2 months ago. I didnt change the frame mount location, I just went out and bought new motor mounts for the block (smae as the small block anyway) and dropped it right in. I have done this 3 times now 2 71 chevelles 1 72. You do not have to move the frame mount location or flip them around just drop the motor in.
 

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1970 Chevelle Convertible & 1965 Chevelle SS Convertible
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Tim,

Back in 1979 I swapped a small block to a big block in my 71 Chevelle - same result as Steven. Just used the big block mounts for the block. Fit perfect.

Rich

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70 SS - L34
Member # 442
www.chevelles.com/showroom/richr1
 

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Kevin,

Your answer is a bit confusing. Does this mean that if you had a 307 and are now going to a 454 that the mounting brackets on the frame are the same and do not have to be moved, but that you just need big block motor mounts?

Please clarify.

Thanks,

--Andy--

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1970 Chevelle SS Convertible
1937 Master Business Coupe
1996 S-10 Blazer

Yup, I'm Chevy Prejudiced!!!!
 

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Kevin, I have the same question. Please clarify. I have been using the same old 307 frame and engine mounts on my Big Block for about 15 years with no problem. If the frame mounts are the same shape and size as the 307 mounts, but built stronger, then that would make sense. I read that same info somewhere, so I just bought new frame mounts for a BB, but have yet to compare them with the original 307 mounts.

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1970 Chevelle SS Clone 502-540HP-560ft-lb
1992 Trans Am Conv(4Sale)
1992 Taurus SHO
Mercer, PA
sswinger.home.att.net/
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Lets make sure we are all talking about the same parts. Engine mounts are a rubber/metal combination that mounts on the block with three bolts. All V8's will interchange, but differ in appearance. The 350 and big blocks have an interlocking safety feature, but the 307 does not. That is the only difference. Other than the safety feature, they are physically the same size. Frame mounts (towers to some) are the all metal stand mounted to the crossmember. They attach to the engine mount on the block with one large bolt on each side. In 68-72 cars, the frame mounts can be used in either big block or small block cars. HERE IS THE IMPORTANT PART!. Although they are interchangable, the engine will sit in a slightly different spot than original if you use small block frame mounts with a big block. It's not normally noticable,but there can be a clearance problem with some headers in some cars. Hooker warns of this problem on the large tube supercomp headers. It's not always a problem, but it can be. We have sold lots of headers with only a small few comming back for this reason.



[This message has been edited by OPGI (edited 12-22-1999).]
 

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So what is the difference in height? Will the small block mounts leave the engine higher or lower?

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1970 Chevelle SS Clone 502-540HP-560ft-lb
1992 Trans Am Conv(4Sale)
1992 Taurus SHO
Mercer, PA
sswinger.home.att.net/
[email protected]
 

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Guys here's what happened with a friend's 70 Chevelle. He had a 307 car and dropped in a 454. The engine motor mounts didn't sit correctly on the "towers" and he had to use some washers as shims. In addition he had some interference between his Hamburger oil pan and centerlink. He called a friend of his at a Chevy dealer and found that the frame mounts have a different part number than those for the other V8s. He got the 350/BB mounts out of a junked Monte Carlo and now everything fits beautifully.

I am not saying you can't make it work, just relaying my experience.
 

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307 frame mounts are a hair wider than other V8 motor mounts. The tech ref here says they're different, and I was a doubter as well until I tried it and my new Energy Suspension motor mounts would not fit down over them. Luckily I found a front end from another car at the boneyard and used those frame mounts and it worked great. I didn't try to use the 307 engine mounts because I wanted something that I knew would keep my 454 in place.
 

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The 307 mounts are smaller than the 350 mounts. My wife's 70 Chevelle had a 307 and my 70 Chevelle has a 350 and both cars were bought new by us in '70. If you put the two mounts side by side, the 350 mounts are heftier. Noticed this the first time I changed the mounts many moons ago. Still have a pair of 307 mounts in the garage.
 

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Help!
yikes I just put my 350 into my 72 ss el camino
(that used to have a big block in it.(402) long gone blown up.
and I used big block motor mounts on the engine( came with the truck.)
(engine just dropped in easy) will i have to change the mounts to the 350 type? i noticed the mounts had a tab on the side of them (interlock?)
as the 350 mounts dont have this....:clonk:
 

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Guys here's what happened with a friend's 70 Chevelle. He had a 307 car and dropped in a 454. The engine motor mounts didn't sit correctly on the "towers" and he had to use some washers as shims. In addition he had some interference between his Hamburger oil pan and centerlink. He called a friend of his at a Chevy dealer and found that the frame mounts have a different part number than those for the other V8s. He got the 350/BB mounts out of a junked Monte Carlo and now everything fits beautifully.

I am not saying you can't make it work, just relaying my experience.
Interesting I have 307 frame stands. I am having a clearance issue with a hamburger pan. It is a SBC and it is very tight to the centerlink. So the answer is to get some new 350/BB frame stands and I should be all set?
 

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Interesting I have 307 frame stands. I am having a clearance issue with a hamburger pan. It is a SBC and it is very tight to the centerlink. So the answer is to get some new 350/BB frame stands and I should be all set?
You can replace the frame mounts or you can use 307 engine mounts that match the frame mounts you have. Why they made the 307 engine/frame mounts different than the 350 & up ones is beyond me.
 

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Interesting I have 307 frame stands. I am having a clearance issue with a hamburger pan. It is a SBC and it is very tight to the centerlink. So the answer is to get some new 350/BB frame stands and I should be all set?
Are the motor mounts that you have on your engine the 307 motor mounts or are they the 350/454 mounts? My understanding is that if you have them matched, you won't have an problems. The problems start when you mix them.
 

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Are the motor mounts that you have on your engine the 307 motor mounts or are they the 350/454 mounts? My understanding is that if you have them matched, you won't have an problems. The problems start when you mix them.
Yea, that's what I was trying to say. As long as the engine mounts match the frame mounts you can use either type.
 

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Hummm... I thought sb/bb motor mounts was the same 70-72 and prob some other years...72 chevelle here, had a 305 in it when I got it but factory 307 car. bought some heavy duty motor mounts the poly ones jegs sell,plated(pretty nice). Besides the fact, went to drop the bb down and the ears didn't want to fit over nicely...pissed me off i wanted to beat it in there lol... pulled it back up put some motovation on the ears, and wahhhhlaaa. fits nicely!!! Didn't have to do any rocket science or move anything or look for other mounts... Running a stock oil pan, no probs here! Can't beat factory! As for engine height no issue's. I think I learn something new everyday when im on here. Love this site, very educational.
 

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I forget exactly where I actually saw a side-by-side picture of an assembled 307 stand & motor mount next to the 350/BB stand+mounts, but I recall the overall heights were the same. They are just not interchangable. So the 307 stand was taller, but had the short, inferior, non-interlocking motor mount.

I had a '67 SS350 Camaro that ripped the driver's motor mount in half and managed to lock the throttle rod linkage wide open!!!! Fortunately, I had the wherewithal to yank the gas pedal and release it. What a ride :noway:

Suppose there was a reason they redesigned them... ya think?
 
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