I'm going to buy cometics .040 thick head gaskets for my stock block with 243 heads. Do I need 3.910 bore or 4.030 bore gaskets and is the 0.3 bump in compression ratio worth the chance in the gaskets leaking (with copper spray)

And what else will I need for the head swap, Don't want to forget anything. I think they are LS2 heads so I could reuse the compcams 7.400's that only have 1000 miles on them. Thanks.

 

I just finished my 243 heads Sat. night with the exact same gaskets, 3.910 bore are the ones. The heads are not LS2, but LS6. This was the third time I have used Cometics with no leaks and no copper spray, make SURE your block surface is well prepped! Your cylinder heads surfaces as well, and don't open the gaskets untill the moment you are going to use them. www.ls1howto.com will tell you what all you'll need for completion. If you need any tips or run into a work stoppage while you are installing them I am quite fresh, so ask away. Good Luck!

 

The cylinder heads I bought said they are brand new/never ran so hopefully they have a mirror finish, I'll clean the block very well too but what is the estimated bump in horsepower from going from the stock gasket with 243s @ 10.65 compression to the .040 gasket @ 10.90-10.95 compression. I'd rather save the $100 and know it will seal if it's only going to be about 5 hp. Thanks.