got a 5.3 Im building and i was wondering if i use ls1 heads what would the compression ratio work out to be, and do i need the 5.7 head gaskets or the 5.3

 

You should always use head gaskets that match your block's bore. The CR will be close to 1/2 a point lower unless you mill the heads.

 

Use head gaskets where the fire ring (metal part of a head gasket) matches whichever is larger. An exposed fire ring won't last long or seal good.

If you have the 5.3 heads keep them, and get work done to them if you've got some $$ to make it faster. WCCH did (not sure if still does) a stage one job that puts bigger valves/mild porting.

 

always match the gasket to the HEADS! Not all ls1 heads are the same on the under side. some are notched and must be used with the corresponding gaskets or they will leak

 

So what happens when you use a 5.3 head on a ls3? (not that you should,be for arguments sake...) Then you have an exposed fire ring from the bottom.