L-48 vs L-82 compression

[john davis]

I have a 1975 L-48 it says 8.5 to 1 compression ratio the L-82s have 9.0 to 1 where is the 1/2 point of compression difference they both have 76 cc heads is it in the pistons? Now that I have the edelbrock 64 cc heads any body care to guess my compression? I dont know gasket thickness all I know is it was a felpro thanks

 

[Tom Bryant]

compression

John, I would guess that the L48 had a slight dish and the L82 had flat top pistons. I'll bet your are in the 10 to 10.5:1 range now. How does it run on pump gas? You should be able to run more timing with the aluminum heads over iron.

 

[john davis]

I run 87 octane with no problem I kinda figured I was tunning around 9.5 to 1 compression

 

[Stingray6974]

Hi John,
59Tom is correct about the pistons changing compression. Your L-48 will have a dished piston with 4 valve reliefs and a beveled outer edge. Posted compression is 8.5 but actually it's closer to 8.2. Fel-pro composition gaskets compress to .039, so with 64 cc heads your comp will be close to 9.3. If you change pistons to L2256, that will give you approx. 9.8. L2417 pistons will give you 10.1
Hope this helps,
Mike

 

[Tom Bryant]

thermal barrier coatings

Thermal barrier coating on the piston tops, combustion chambers and vavle faces will greatly reduce detonation and allow more timing as well as keep the heat in the combustion chamber making more horsepower. Might be cheaper than new heads but a lot of work. Worth asking, I guess.