Did any of you horsepower calculator guys ever use this

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

As for the HP calculator, I just use the 1.4 cfm per hp rule of thumb and the cid x rpm/3456 = cfm, to get ballpark. So if I wanted a 400 hp engine that peaks around 5000 rpm would be 400 x 1.4 = 560 cfm so 560 x 3456 / 5000 = 387 cid.

Click to expand...

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”.

This one is going the other way.....
420hp motor at 6200
420 x 1.4 = 588
588 x 3456/6200 = 327.7ci

Motor is 365”

Of course, that motor made 399.5hp@5100....... which shows it would need to be 379” to get it done.