Engine mounts and frame mounts, 455 doesn't fit


Asked by Sep 07, 2015 at 07:52 PM about the 1966 Pontiac GTO Coupe

Question type: Car Customization

I have a 66 GTO and it came with a 455 cid, one of the engine mounts was
broken, so I didn't think much about it, now that I'm rebuilding the engine I
saw that the mounts don't line up, I have the stock 389 engine mounts and
original frame brackets. The engine doesn't fit, it's about 3/4" to wide, so the
mounts font line up.  I thought you could drop a 455 in place of a 389 with no
problems. Any suggestions? Stuck here.  Thanks in advanced

5 Answers

Kelly Mayo

change the mount towers on frame...


In 66, the 389 was the only GTO engine option so your 455 must have been transplanted later in its life causing the mount problem. The options available that year were a 389 4BBL, a 389 with 3 deuces, and a 389 HiPo with 3 deuces.


The 455 is a transplant. It came with the car when I bought it. I'm just trying to get it to fit the mounts now. No combination seems to work. I have the 389 style mounts and frame mounts, but the block and mounts seem to be about 3/4" to wide when one bolt is in.


What mounts should I switch them out with


I basically have! The same issue with my 80 lemans wagon a few years ago. Earlier Pontiac motors have only one set of bolts in the block for engine mounts. Then there was two bolt patterns in 1970 for the new f- body chassis. If I remember correctly. Then later years dropped the early bolt holes and they only had one set of holes in the block. Not sure what year that changed. My earlier block (68 ye code 400) only had the early bolt holes. I had to fabricate my engine side mounts from 301 mounts. If it were me I would locate a set of mounts from a later model engine 70 up and get some later towers and try them. May need to drill holes in the frame for them. Your block will be a 70 on up (70 was first year of the 455). Would look into a matching set of newer mounts say 75 grand prix or so and try them, both engine and frame halves. That should get you on track. Thanx Pontiactivist.

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