comp ratio on pump fuel

[aussie455]

I wanna get a set of stage 2 heads for my 455 which I believe bump the compression up to about 12:1. Is this to high? What's the highest compression you can have and still run on pump gas? Does it vary from engine to engine?

[anychevy]

I wanna get a set of stage 2 heads for my 455 which I believe bump the compression up to about 12:1. Is this to high? What's the highest compression you can have and still run on pump gas? Does it vary from engine to engine?

12-1 is high, but with the right cam, and ignition you could probably get away with running on 100 octane (if you can get it)
But just changing the heads to a smaller chamber to increase compression to 12-1 ?
You'll have to retard the timing so much it'll run like crap :(

[aussie455]

Just noticed I posted this thread in the general discussion. Doh.

So what compression should I run? 11.5? 11? I just want throw some 98 octane at it and expect it to run.

[anychevy]

Just noticed I posted this thread in the general discussion. Doh.

So what compression should I run? 11.5? 11? I just want throw some 98 octane at it and expect it to run.

What 455 is it ? If it's pre 71 it should be around 10-1 ? which is good for 98 :D
Give it a little more spark advance, just till it pings and then back it off a couple of degrees and see how it likes it.

[aussie455]

What 455 is it ? If it's pre 71 it should be around 10-1 ? which is good for 98 :D
Give it a little more spark advance, just till it pings and then back it off a couple of degrees and see how it likes it.

nah it's post emissions:(

[anychevy]

nah it's post emissions:(

I'm not that familiar with Buicks, but maybe early model closed chamber heads will bump the CR up ?
But you'll have to do the research and math to get it about 10-1 :confused:
Otherwise it's new pistons, so you might as well call it a rebuild.

[aussie455]

yeah I sought of want to avoid doing that. So what is the max cr I can have? 11:1 would be alright wouldn't it? Like if the heads I get take compression up to high, I can just chuck a couple of extra gaskets in there couldn't I?

[anychevy]

yeah I sought of want to avoid doing that. So what is the max cr I can have? 11:1 would be alright wouldn't it? Like if the heads I get take compression up to high, I can just chuck a couple of extra gaskets in there couldn't I?
what CR is the motor now ?
There are ways of getting more HP from a low (say 8-1) compression engine with the right cam, intake, carb, exhaust and without changing the heads.
If you've got large chamber, small valve, smog type heads then maybe ?
11-1 would be about the limit on a stock engine, any higher and you'll have detonation problems :mad:
Yes you can use 2 gaskets on each head to lower the CR

[OzRiv]

Stage 2 buick heads?......didn't they make only about 75 sets...sold hush hush over the counter and undocumented?

[aussie455]

Stage 2 buick heads?......didn't they make only about 75 sets...sold hush hush over the counter and undocumented?

Nah TA performance make them and the stage 1's aswell and in alloy too.