Did any of you horsepower calculator guys ever use this

Another one for ballpark I made up takes guesstimating the engines torque to cid ratio and where the engine peak hp rpm will be and torque at peak power will 90% of peak torque.

So if you where building say a 451 cid and figure the collection of parts your planning on using would make about 1.2 lbs-ft per cid and peak power around 5700 rpm.

so 1.2 x 451 x 90% = 487 lbs-ft
487 x 5700 / 5252 = 529 hp

So 529 hp @ 5700 rpm
and 541 lbs-ft @ 4300 rpm

Like you said there's gonna be a lot of wiggle room since you got to guesstimate two things and that engines torque will be 90% of peak torque at peak hp.