Frame Question

[biohazardbill]

What is the difference between a 66 and a 67 frame as far as motor mounting goes? I thought all the cradles/frames were basically the same for these years.

Currently in my 66 I bought some CPP perches to mount a big block in. I had to do some frame trimming etc, however reading in some of the other forums to do a 454 swap into a 67 you can use perches specificaly for a big block from later model trucks. Why wouldnt we use these same perches in a 63-66?

[Captainfab]

There is no reason not to. I most always use factory motor mounts and brackets. The '63-'66 and the '67-'72's have the same hole configuration for the motor mount attachment. The one difference in the frames, is that starting in '68, when the big block was first available. the top flange of the frame was narrower that the earlier years, to allow cleaeance for the big block exhaust manifolds. So the earlier frames should be trimmed to accomodate a big block. Some guys get away without though.

To install a big block you can use either the '68-'71 big block motor mount brackets, the '72 only big block mounts, or the '73 and up clamshell type motor mounts. If you choose the '73 and up, the motor mount brackets from a C20 fit the early frames better than ones from a C10. The C20 frames are shorter in height than the C10 frames, and more closely match the '72 and earlier frames.

[biohazardbill]

I notice in the 73 and up you did not specify big block mounts. Does this mean either the small or big block mounts will work?

When you say and "73 and up", do you mean up to 87 or higher?

Thanks for all the help...

[Captainfab]

With the '73-'86 C series and '87-'91 R series motor mounts they are not specific to either small blocks or big blocks. They are all the same. The only difference is in the height of the frame brackets between the C10's and the C20/30 trucks.

[rustyrodknocker]

Why did I have to move the motor mounts when I put a big block in a 68 4x4? There was an extra set of holes or something. Anyway the motor needed to move forward or rearward don't remember which or why. But the holes were there and it worked perfect.
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[Captainfab]

That's because GM never put big blocks in the '67-'72 4x4's. You either have to modify the firewall or move the engine forward. Also those motor mounts are totally different than the '73 and up motor mounts.

Originally Posted by rustyrodknocker

Why did I have to move the motor mounts when I put a big block in a 68 4x4? There was an extra set of holes or something. Anyway the motor needed to move forward or rearward don't remember which or why. But the holes were there and it worked perfect.
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[rustyrodknocker]

Originally Posted by Captainfab

That's because GM never put big blocks in the '67-'72 4x4's. You either have to modify the firewall or move the engine forward. Also those motor mounts are totally different than the '73 and up motor mounts.

Did not know that. Wonder why? Also spins me into another tangent. Has anybody ever posted an as the factory coulda woulda done ? Say 396 in a 66' ? Now I'm not going get any sleep at all. Sorry for the hijack Biohazzard.
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[biohazardbill]

Last question... hopefully lol

Will any of the motor mounts you listed above interfere with block hugger headers?

I currently have Chevelle headers but block huggers would help me route the exhaust easier the way I want.

[Captainfab]

The '73 and up motor mounts will not work with block hugger headers.