WOW!!!! You guys are all great, thank you all so much for giving me so much information!!! I cant thank you guys enough, you have helped me in so many ways, already my car is running better and everything!!! Thanks again,
-John

 

$20 is an incredible deal, but my engine is pretty new, im not sure if i need them right now, my car is at my friends shop getting some new little things put on, i have to check tomorrow when i get my car to see if i need them, if i do i will defeintally buy them, but if not then thank you anyway, you are a really huge help!

 

Hey ws6transam.. even the LG4's had a 9.5:1 compression. Not only the L69's. Just thought I would inform you.

 

You might be partially right.

According to the 1984 GM service manual, the L69 sports a 9.5:1 compression ratio whereas the LG4 (VIN code H) sports an 8.6:1 compression ratio. Further, the L69 has a tigher specification on valve seat width of 1/32 to 1/16 whereas the LG4 has a valve seat specification of 1/16 to 3/32, which would indicate that perhaps GM threw an extra valve machining process into the L69 heads. I hadn't gone much past the 1984 specs before. However, this is what I found when I did:

The two engines use different pistons: The L69 uses a cast aluminum piston which is a flat-top, four relief design ( P/N 14081291) , whereas the LG4 uses a dished cast aluminum piston (P/N 364702).

At least, that was the case through 1984.

Then, in 1985 through 1986, GM changes the LG4 (known as the 305H engine) to use the 14081291 piston, which raises the potential compression ratio. All three 305's use them for those two years: VIN F, G, and H. However, ??Guess What?? The Canadian market LG4's are still saddled with the 8.6:1 compression ratio P/N 364702 piston.

Then, in 1987, a new change: The 14094013 piston gets used by the 305H (LG4) and the 305F (TPI) engine. The Canadian LG4 engines also get a different piston, the P/N 10049082, so they are probably still saddled with a lower compression version of the 305. The piston change is probably due to the new centerbolt cylinder head designs:
The 1987 through 1992 305F (LB9) and 305H(LG4) used cylinder head P/N 10159553, whereas the 1988 through 1992 305E (L03) used cylinder head P/N 10159551.

In 1988 through 1992, both versions of the 305 get the 14094013 piston, and there is no mention that the Canadian versions get anything different.

So, although it looks complicated, the news is that before 1985, the LG4 was 8.6:1 compression, whereas afterwards, it looks to have been bumped to 9.5:1 compression ratio.

One note: All 305's use head gasket P/N 10105115 from 1982 through 1992. This is a 0.015" thick, coated steel head gasket. If you ever open up your engine, remember to use a similar gasket and NOT a regular ol' 0.041"thick smallblock chevy head gasket, or your compression ratio will suffer a serious drop.

 

I know for a fact that the '85's and up use 9.5:1.. but thanx for the additional info, that was very helpful. Would a gasket-kit by Felpro or whatever have .015" thick head gaskets?