compression 455 olds

[dgie]

I did a compression test on my motor yesterday and the cyl had between 127-140 psi is this good I know about the 10 percent between cyl, most however most seem to hover around 127-130 one is at 140 (outlier). I was told that it is probably just sealing a little better then the others, is that sound right? Also how do you bump up the compression on a motor? I have a stock setup, so I assume I am running low compression pistons (dish on top) could you put in better pistons and cam to bump this compression up? what does it do for the motor overall?

[Wally_Gator]

Up the compression ratio?
There are several ways to do it...
1. Mill the head
2. Deck the block
3. Different Pistons.
4. Thinner head gasket.
These are some of main ways that compression ratio is adjusted. Usually all of them ar tweaked to achieve a desired compression ratio.

[IDK]

My 455 is a 390 hp crate engine from 1970 and a year and a half ago my compression test had 190 in a few cyl and 200 in the rest I think my engine is 11 to 1 comp. If you want to raise the comp. you should change the pistons the standard piston in a 455 has a dish that is about .300 deep the dish in my pistons is about .100 deep I hope this helps you . Roger

[dgie]

Up the compression ratio?
There are several ways to do it...
1. Mill the head
2. Deck the block
3. Different Pistons.
4. Thinner head gasket.
These are some of main ways that compression ratio is adjusted. Usually all of them ar tweaked to achieve a desired compression ratio.
Wally Gator, I am a learner here, when you say mill the head what does that entail and also when you say deck the block what does that mean? Also what is the benefit of a higher compression?

[Wally_Gator]

Wally Gator, I am a learner here, when you say mill the head what does that entail and also when you say deck the block what does that mean? Also what is the benefit of a higher compression?
Milling the head and decking the block both require complete motor disassembly. You then take the heads or the block to a machine shop and they will then take off a feqw thousandths of an inch. this does two things..
1. Ensures a perfectly flat sealing surface.
2. reduces your combustion chamber size on the heads.
Compression ratio gains you more hp at the cost of having to run higher octane gas among other things.
I measured my heads, (cc'd) as well as the deck height. There is a formula that includes all of the following:
Head combustion chamber volume
Piston dish volume or negative volume as in a domed pistion.
deck height (piston top to the top of the block)
thickness of the head gasket.
Stroke of the crankshaft.
size of the cylinder...
I am set at 9.56:1 on my olds.
It rungs strong and I run 91 octane gas.
We are still tuneing the carb. It would have been done sooner. But have to have some fun in the process as well as a bad fuel pump gave some faulty readings..
Looks like all I need now is a different power valve and I should be set.
I hope this helps.
Walter (wally_gator)