Needin' some help trying to figure what my compression will be when I get my heads back and using various gaskets. I found this webpage, http://www.smokemup.com/auto_math/compression_ratio.php

I have no idea what any of the numbers should be for a stock LT1. Anyone know?
Thanks
Jeff D.

 

I found this site that calc. for f-bodies. Still need the piston dish volume on a stock piston. Anyone?? Using the default setting gives a 10:91:1 ratio which I believe is high.

http://www.gafba.com/calculators/cmpratio.asp?mode=ntr

Jeff D.

 

ne1?

 

how about today?

 

dobedo...anyone today?

 

Bore: Stock is 4.00. If cylinders are .030 overbore: 4.030

Stroke: Stock is 3.48. A 383 istoker is 3.75"

Rod Length: Stock is 5.7". Some use 6" rods on 383 rebuilds

Cylinder Head Volume: Stock is about 56cc. May be larger after bowl work. Check head volume with machinist

Deck Height, Gasket Bore, Ring Land Height, Cylinder Wall Clearance: Use Default Numbers.

Gasket thickness: Fel Pro: .039", Impala: .029

Piston Dish Volume: Stock pistons are flat tops so volume =0

Hope this helps

 

Thanks for the reply. Still getting over 11 to 1 when I type in the stock numbers. The calc on the website must be wrong or something.

Jeff D.

 

All right, Poorman, I'm going to attempt to clear this up... Yes, the stock LT1 has flat-top pistons, but they have valve reliefs cut into them, which has to be taken into account; AND you have to account for the .025" the top of the piston sits below the block deck surface. Let's just start from stock, shall we? A stock LT1 has the following specs:

Bore: 4.00
Stroke: 3.48
CC's per cylinder: 716.6cc
Combustion chamber volume: 54.8cc (as quoted from Phil, I'll definitely take his word for it)
Compressed head gasket thickness: .050"
Compressed head gasket volume: 10.95cc
Compression ratio: 10.5:1

Using the compression ratio formula backwards, you end up with a total combustion area of 75.4cc.

If you're still using the stock short block (stock pistons, block not bored/decked, etc.), all you need to do is add/subtract the number of cc's in the areas that you're changing.

In my case, my combustion chamber volume changed to 53.6cc and I went to the Felpro 1074 head gasket; .039 compressed thickness and 8.54cc volume. Before you say I calculated that wrong, remember that you have to use 4.125" for the bore size of the head gasket.

OK, with all that being said, my total combustion area changed to 71.79cc. Then, it's back to the compression ratio formula, and I get a 10.98:1 compression ratio. I know, long post, but I hope it helps a little.

 

piston to deck clearance is an issue too

 

You got that formula handy? Thanks for the reply. That will help alot if I can see what formula you are using.

Jeff D.