I recently came across a 76 455 4bbl engine and was considering purchasing it for my 69 Convertible which has a 350. A couple of questions:
- Will this bolt up the same as the current Pontiac 350?
- Is the 455 an internal balance engine such that my manual transmission flywheel will bolt up?
- The compression ratio is low, 7.6:1 what is the easiest way to increase this to around 9:1 or so to maximize the engine power?
- What is the most cost effective method to increase the performance of this engine? It is currently only rated at 200 hp @ 3500 rpm and 330 ft-lbs @ 2000 rpm.
- Are there any known problems with these engines that I need to keep in mind?
Thanks,
Tom

Should bolt right in. Pontiac 350,400,428 & 455 are basically the same block (differnt bores & stroke). You can up the compression by changing heads or milling the ones you have. There are a lot of other things you can do to increase HP, depends on what your tryin to do.
Later blocks had lower nickle content and arent as strong as the earlier blocks.

Per Wallace:

http://www.wallaceracing.com/engine.htm

all 455's have 5 mount holes so they will go in pre-70 and 70 and up cars (with the correct motor mounts).

You can run into trouble installing a mid 70's and later 400 into a FGF if it only has the new mount config.

thought about doing the same in mine, I found a 76 455 and was thinking about using my 670 heads on it in order to get compression down from the 400 they are on. Hope we're not looking at the same one. I found one on cl

Using 670 heads on a 455 will result in about 12:1 compression. This is WAY too high for any "pump" gas. 110 ONLY. Unless a "race car", not a good choice.

Milling .060" off the current 6X heads (or are they 6Hs?) will get you CLOSE to 9:1. If 6Hs, find some 6X-8s... 6Hs can't be milled "enough" to raise the compression without compromising the intergity of the head's "deck surface".

In lower compression engines (under 9.5:1), we use Comp XE cams. For the 455, XE274H is a good choice. It offers good power and a fairly "broad" band, as well as a "hint" of a lope.

Very important: Before buying ANY parts, consult a true Pontiac "builder" to assure the combination is good. More Pontiacs have been abandoned or blown up due to a "bad combo" than any other reason. Each of us has our own "approach", so "mixing" builders' advice may not be a good idea. Pop always said "Pick a horse. And RIDE IT!"

There is nearly an unlimited amount of modifications that CAN be made. The '76 block should be kept under 600 HP, though. It's the "lightened" version (less iron).

Jim

The engine is a 76 455 with 6H heads and roughly 76k miles. I saw this on the St. Louis craigslist so it likely is the same engine.

The engine appears to be in fairly good shape but finding a decent set of heads seems to be pricey. Is the 455 worth the extra cost? The low compression, 7.6, has got to be a performance killer and most heads will put the compression way too high as you stated.

This would be for the street. The car presently has a TKO500 5 speed with 4.10 gears in the rear. I also have a 2.78 posi rear so the torque of the 455 was attractive. But I suspect the current gear would be too much for a lower rpm engine.
Thanks for all the responses.
Tom

I found some that were a little cheaper on KC craigslist, I'll probably keep my 670's on the 400, that 455 is just 20 minutes away if you need someone to check it out, I drive by it twice a week to take my son to baseball practice. I have a set of 6x heads that would fit it