Been doing some reading on the subject of quench and belive I have a basic understanding of things (there is a good thread on going now), My current build is a sbc 383 with 4.030 bore and forged pistons . My target quench is .045 .
With a Mr.gasket ultra seal I can acheive this with .028 in thickness with a bore of 4.130 in the gasket .
I can get the same thickness in a copper gasket with a bore of 4.060 but am under the impression that copper may not be the best choice of materials for a street car .
If i give up .012 of quench and go to a .040 thickness I have a wide variety of choices of materials and bore sizes . Dont really know what the optimum bore size for the gasket would be .
The short block is done so I really dont want to go back to the machine shop .
Thanks for any suggestions

If you don't mind spending some additional cash for the head gaskets, see what Cometic has to offer. They have most anything and can also make them to spec. Depending on your specifics, you can likely get the quench down to .035" quite safely if you'd like. This is still a very safe number, assuming proper piston fit for a N.A. street engine and also assuming your piston to valve clearance is not already teetering on the borderline, etc.

Somebody correct me if I'm wrong, but I believe you need o-rings when using a copper gasket to fully seal the bores, and there are other things you need to do to the block and/or heads to use them. In any case, from what I understand a composition or MLS gasket is better suited to a street engine than other materials. If you can achieve your target quench with the Ultraseal, then why not use it? It'll be cheap, effective, and the correct size. I don't think gasket bore is vitally important as long as it's greater than the cylinder bore size (obviously).

In fact, it seems you and I have very similar engines. I'm also building a 383 at the moment and will be using the Ultraseal .028 gasket to get me to .045" quench.

Of course, if you want to dial it in some more, there are other companies out there (like Notorious mentioned) that might be able to help you, but you'll have to spend more.

I used the Fel-Pro 1094 Rubber Coated Steel Shim, 4.100 in. Bore, .015 in. Compressed Thickness. Gave me a .040" quench.

BBP