Alright, I'll be doing an STS kit in the next few months and have a question about head gaskets. The engine is a 2003 LS6, completely stock with all the bolt-ons. The STS has the GT67 upgrade, a FMIC and meth injection. I'm swapping the 243's for a pair of 317's to drop the compression and going back to stock manifolds with hollow cats. I have a new pair of GM graphite head gaskets as well as a new pair of GM 6.0l MLS gaskets. First, can the graphite LS1 gaskets be used on the 317's or is the chamber too big? Second, without going to Cometics, would the slightly thinner graphite gasket and the slightly better quench be a better choice than the MLS gaskets or won't the graphite hold up under boost? With stock pistons I probably won't turn the boost up much past 8 or 9 lbs. Thanks!

 

I'd use either the 6.0L or the new 6.2L 5-layer GM MLS...

 

How thick are they? I think the graphites are around .050" and the MLS are something like .052"-.054" I believe. I read on here somewhere that our engines average around .004" out of the hole. This puts the quench at .046" with graphite and .048"-.050" with the MLS. None of those numbers are great if you ask me, but it seems the Cometics don't like to seal too well with anything less than a perfect mating surface. I'm just trying to optimize my quench to try and stave off detonation as best I can with stock pistons. Not that forgings can hold up to severe detonation either, but they do a little better.

 

I'm running a TT set up on a 347 cubed LS1 with 317 heads. With a stock bore size, I always heard you will get a better seal if you match the gasket to the block bore size so I would go with the 2002 -up MLS stock LS6 GM gaskets or Cometics same size.