DanielRicany

Hey guys, I want to know what my compression ratio will be. I've been using online calculators but they seem to give me confusing and varying answers.

My car is a 1985 Corvette. The engine specs are:

Bore: 4.000"
Stroke: 3.48"
Head Gasket Bore Diameter: 4.100"
Compressed Head Gasket Thickness: 0.015"
Combustion Chamber Volume: 65 CC
Flat Top Pistons
Deck Height: 0.025"

Thank you!

cumbercr

10.2:1

don hall

http://en.wikipedia.org/wiki/Compression_ratio

vetteoz

Are they true flat tops?
Most "flat top" pistons have at least 2 valve reliefs, the volume of which has to be added to the equation

DanielRicany

They should be for 1985. I haven't looked at the pistons yet.

cumbercr

I included +5cc for stock pistons with valve reliefs.

Rohn

I recall the relief is -6cc...

cumbercr

The pistons would have to be domed for -6cc.

Rohn

I believe (-) refers to the valve relief. (+) would be domed...

Am I wrong on that?

cumbercr

It's just the opposite. Add for valve reliefs and subtract for domed. Reliefs increase the volume of air being compressed.

DanielRicany

I read online in a few posts where people said the valve reliefs make up 4 CC, so I typed that into the calculator and got 10.28:1, would that be accurate? Then I can just say 10.3:1 CR.

cumbercr

Since you only have an estimate of your deck height I would say that's close enough for now.

Rohn

Cuc: you are correct. It is piston head volume that is advertised. so a dished flattop for valve relief is in fact a positive number. I see it being +5 cc.....

cumbercr

The SRP flat tops used in my 396 were advertised as +5cc. But I've also seen flat tops with one long relief that were +7cc.

wilcar

What heads do you have on your 85? Stock heads would be the 76 cc 624's. Your stock pistons should be trw forged units with a trough. Where are you coming up with 64cc combustion chambers?? Compression ratio on a stock 85 would be around 9.0, same as an 84.

DanielRicany

AFR 195 Heads

wilcar

Great choice!!

DanielRicany

Thanks! I followed the recommendations from a lot of people. Shooting for 450 hp, but I'll be happy with 430. If I go to a roller cam, and I don't know the exact cam but it's one made by comp cams, it was proven to make around 500 ish hp I believe.