as one old f--- to another I use .020 to .022 on the top with any bore over .4.3 and .024 to .028(depending on the exact application of the motor and its induction system or power adders and so on) on the second rings. Looser ia always better than to tight on a race engine, especially on ring gaps! My 512 stroker 400 block (9.25 to 1 comp. on pump gas) makes 609 hp on the DTS engine dyno at 5600 rpm with ported 906 heads.