A friend of mine is looking at getting an 86 Iroc. It has the LB9, 305 TPI engine. The engine has a bad head gasket, and to get some more power out of it we are thinking of putting in a thinner gasket. In another thread I read about using a FPP-1094 Shim, and that it is a .17 thickness, compared to the stock .32. How much will this raise the compression in this engine. It has the original heads on it, 58cc. Another problem is that this block is already a .030 overbore. Will this head gasket work on this engine. Won't the size of the hole for the piston in the gasket be wrong? What other gaskets would you guys suggest to raise the compression a little bit?

 

You'll raise it about .2

I would not recommend steel shim gaskets unless the block and heads are VERY flat. They are much tougher to seal up than a composition gasket.

 

Screamer,

At 0.030" overbore, you're already at 9.6:1 static (with all other things being equal). Unless the replacement pistons were different than the stock cast pistons (domed, only 2 reliefs, etc.) the 9.6"1 should be correct with a 0.032" head gasket.

I'd tend to agree with Damon. A shim gasket on a street engine can be a problem. They can work out just fine, but the tendency to allow creep and leakage is greater. If you're going to pull the heads to replace gaskets, a little trimming of the heads usrface is a safer way to increase compression, if you really want to. Approaching 10:1 on pump gas can be a little problematic with a batch-fire system and our older ECMs. Spark retard is not as refined as the newer PCMs, so there may be a net loss unless you are willing to run higher octane all the time.