Decided on the 455 - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 08-11-2013, 08:12 AM Thread Starter
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Decided on the 455

Hi folks after month of trying to decide between the 455 and 400,I decided to redo the 455.The car is just a street car. My question is which heads should I use for the 455.
I have three sets of heads a set of 6x-8 a set of 6x-4 and a set of 64's
what combo will give me the best cr for pump gas.

Thanks in advance
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post #2 of 4 (permalink) Old 08-12-2013, 07:48 AM
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I recommend the 6x-4's. At 94 cc's chamber volume (please DO measure and verify yourself!!) on a +0.030 455 with flat top pistons and everything else "factory nominal", you'll be right at 9.3:1 compression ratio which is dang near perfect for pump gas.

If you're going to be replacing pistons "anyway", then consider having the block zero-decked and using pistons with D-shaped dishes and having a total of 10 cc's additional volume in them. That'll still have you at 9.3:1, but with the added benefit of excellent quench area characteristics (helps combustion efficiency and provides additional detonation "insurance".)

Another option: If you do zero-deck the block and use the 6x-8's instead and flat top pistons, you'd wind up just a hair shy of 9.1:1. You'd be leaving a little bit of power on the table (but not much, probably just a couple of HP) and still be getting the benfit of better quench.

Yet another option: Run the 6x-8's but have them milled .015 (again DO measure the volumes first so you know for sure where' you're starting from!). Your goal here is to get the chamber volumes "down" to 98 cc's (from factory nominal 101). Zero deck the block, run flat top pistons. This would put you at 9.3:1 and give you excellent quench properties.

Point is: You've got some very good options available to you depending on how much you want to spend on machine work and also the availability of a good machinist who knows this isn't "just like a chevy".


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post #3 of 4 (permalink) Old 08-12-2013, 08:27 AM Thread Starter
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Thanks Bear
Sounds like first option the way to go and saves me a few bucks from not machining the 6x-8's. That leaves me with a set of 64 heads that the castings check out good but need a rebuild. Any idea what they may be worth I know they are hard to come by these days.
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post #4 of 4 (permalink) Old 08-12-2013, 09:48 AM
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Roy, I was looking for some 64's awhile back for my 400, as they are the perfect bolt on solution for today's fuel. They came on 1970 GTO's with the 455. They used to go for about $600-$800 a pair, ready to run. I ended up cheaping out and buying less expensive heads. Long story short, they are worth what you can get for them. Bare and needing rebuilding? Probably less than $400. The availability of quality aluminum aftermarket heads has devalued some of the old stuff. The cost of rebuilding an old set of iron heads can easily approach the cost of a brand new set of aluminum ones. Don't ask me how I know!
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