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Discussion Starter · #1 ·
I am putting a big block to my original 307 '68 Chevelle. Do I need to change the mounts where the block bolts to the frame?

Also, would you recommend solid mounts for a high HP and torque engine, or would polygraphites do? Anyone has experience with the PST polygraphite, or ES polyurethane mounts?
Thanks for you help.
 

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You will need to find engine frame mounts from a 68-72 Chevelle 350 or BB car. 1970-72 Monte Carlo's also have the right ones. They all had 350's or 402/454's. Your 307 mounts will not work. Good luck in your hunt.
I am using Energy Suspension's motor mounts on my 69 SS396 and they are awesome. I think I feel a little bit more of the engine, compared to rubber mounts, but I feel a lot better about having them in there. I'll be putting them on every car I build from now on.

Nate
 

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yanniz
Nate is correct in the fact that the two stools are different. I went this round with my small block install.
The 307 frame mounts are about 1/2 inch taller than the 350/BB frame mounts.
I installed polygraphite motor mounts in my car and found out there are two kinds of the early style motor mounts. Short/wide and tall/skinny. With the short 350 mounts and the short/wide motor mounts my oil pan hit the cross member
Luckily I had a pair of 307 frame mounts. I had to put the 307 mounts on the frame to gain oil pan clearance with my short/wide motor mounts. This was quicker than returning the mounts and ordering the taller ones.
I have heard of several TC members putting a BB on top of 307 stools. There are really two variables; stools and mounts. Unless you need to be absolutely "correct" there may be more than one way to set that engine in. Keep in mind it's a real PITA to change the stools if the nuts haven't been tack welded inside the crossmember (the factory doesn't do that). The perfect scenario would be to have both motor mounts and both stools on hand, but with your 307 stools, I'd start with the short/wide poly mount. Then if it's too roomy under the oil pan go to the short stool.

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Doug, Chevl71
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The P/N for the 350/454 frame mounts are 3980711, 3980712.

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Tino #28 Gold
72 Malibu 350-300,700R4
83 Grand Prix LJ 305
 

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Discussion Starter · #5 ·
Thanks for all your help guys.
Has anyone put a BB on the 307 mounts. Also, the car had a 350 in it when I boutght it. Could the previous Owner have change the frame mounts to the 350/454? How can I tell which ones they are?

Thanks again.
 

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I have put big blocks in both chevelles and novas with the 307 frame mounts. No problem, just make sure you have the 307 engine mounts to match. Headers always have fit fine, even in the novas where clearances are much tighter.

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Dave (NY)
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
72 chevelle
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Never forget Earnhardt!
 
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