417 Head Gasket size
 

Looking for a double check here, I have a 417 LS3, 4.075 bore, 4.0" stroke. Pistons are -10cc dished.

Advanced Induction has finished up my heads, 280cc with a 75cc chamber.

I want to run thinner heads to keep compression up.

Cometic .040 comes in 4.100 bore, that'll work for this build?

Thanks!

That’s a good combination right there

You'll want to check the chamber on the head before you order a gasket to make sure there is no gasket hanging into the chamber if it's larger than the bore.

Best way is to put Dykem on the deck of the head then put the bare head on the bare block and from underneath, lightly scribe the bore on the deck of the head. You can also reach up inside and feel if the chamber is larger than the bore.

Then place a stock gasket on the deck and see where it sits. The gasket bore should be at least .005" larger than the chamber or head whichever is the bigger of the two.

Also, you can have Cometic make a gasket with whatever bore size you want. They may even have a "standard" part number for it that Summit or Jegs carries, but may not have it listed on their site/catalog.

Agreed! Go for it.

KW

I agree, he might be safe, but it doesn't hurt to double check.

The reason I stress this is because in the OP's original post, he said the chambers are 75cc's. That sounds to me like the chamber could possibly fit a larger bore than 4.075". If that's the case and the chamber is sized for a 4.125" or larger bore, then the 4.100" gasket will be hanging in the chamber by .0125" or more per side.

Probably not a huge deal, but I wouldn't want to chance it.

If the chamber is smaller than the bore, the he could go the other way and run an even smaller gasket and gain as much compression as possible while also reducing the "crevice volume" and help emissions and knock sensitivity.