it really depends on chamber style, valve job angles, valve back profile, port floor height, and operating range with a respect to cros ssection and displacemnt.

usually 92% on the intake and 89% on the exh,, with 45 degree seats and atleast a 30 degree top ngle thats .060 or so wide,, nothing flatter for a top or else you make the throat smaller. if its a flat machined chamber you make the throat smaller, if its a 30 degree seat you make the throat smaller,,, if its a 55-58 seat you make the throat larger..

also depends on seat width,, if its a true sreet car you run wider seats to help dissipate heat off the valve head,, so then you make the throat smaller,, if seat widths are .050 or wider, the above 92% intake is for a .035 or so wide seat, exh .045


if you take alot of factory heads and goto oversize valves you can get into trouble going 92% cause the casting wont support it, the bowl cant be made large enough.......