Did any of you horsepower calculator guys ever use this

PRH said

15:1 580, 360cfm Heads.......
Calculator HP - 721
Actual HP - 828



828hp motor that peaks at 6400rpm.
828 x 1.4 = 1159
1159 x 3456/6400 = 625.8ci

But the motor is only 580”.

918hp motor that peaks at 6800rpm.
918 x 1.4 = 1285
1285 x 3456/6800 = 653.0ci

The motor is 572”.

Click to expand...

Think your talking builds above the 1.4 cfm rule of thumb, think it's mainly follows engine under 1.2 ish and under hp per cfm. Those engine you just listed are 1.43 and 1.6 cid hp per cid I imagine the torque to cid is way up there plus VE% BSFC etc...

The 580 would fall under the 1.3 cfm

828 x 1.3 = 1076
1076 x 3456 / 6400 = 581 cid

572 using 1.2 cfm

918 x 1.2 = 1102
1102 x 3456 / 6800 = 560 cid