The magnum heads respond real well to porting. I have a 5.2 with ported magnums with the 1.97 in valve and they flowed 241 cfm at .500 lift. My little 5.2 with a ported m1 efi intake, hooker headers, 210/220 @ .050 cam and 8.86 to 1 comp ratio put down 290 rwhp. It ran a 13.69 @ 101.xx with a 2.94 gear. I figure about 340 at the flywheel with 15% loss. I wouldn't underestimate the power they can support.
