Disappointed magnum head flow numbers....

Just for comparison my 470 stroker Dynoe’d at 655 hp. Heads flow 320 cfm. I believe the formula is 2.06 hp per cfm. Mine is actually pretty dam close. Volumetric efficiency was 108%. I will add that some motors put out beyond expectations while others fall short. I can’t stress cylinder prep enough. Having straight round bores is an absolute must. Kim