why the limit of 9.5:1 built a teen-3 1 ton truck block with 68 flat top rv pistons and 340 j heads (63 ccs) and used felpro gaskets as i rember it figued out to about 9.6:1 used 88 oct reg gas back then now running it on 87 u/l crap with 8 degrees advance and 36 degrees total mach advance and about 15 degrees vac. advange with out and problems