the 308's are essentially a smog 360 head with a magnum exhaust port. the bigger pushrod pinch needed for the roller lifter's poorer pushrod angle induced some swirl into the ports.

the 302 is a closed heart shaped chamber, small valve 318 head. good for compression, but it flows as poor as any 318 head. max ported with bigger valves, they flow about the same as OOTB magnums.

magnums outflow any stock head save the X's, which they about match on the intake side, but outflow on the exhaust. with a smaller port (more velocity, which means more torque). they also have a nice small closed chamber with dual quench pads.