Originally Posted by Hillbilly bike
Using available formulas and plugging in my engine specification comes up with different results.

Engine Pro - Intake Port Length is 14.02 inches
Gordon Blair Formula - Intake Length is 10.69 inches
Simplified Chrysler Formula - Intake Length is 11.67 inches
Simplified Chrysler Formula (with bigger cam) - Intake Length is 11.15 inches
Simplified Formula - Intake Length is 11.00 inches
Simplified Formula 2 - Intake Length is 13.60 inches
Simplified Formula 3 - Intake Length is 12.83 inches

Obviously a formula is only a quess and time spent on a dyno and at the track is the only way to know for sure.
There appears to be two things happening at once from intake and or velocity stack length.
Longer length appears to move peak HP to a higher rpm and moves the torque lower and flatter at the same time.
Shorter length does just the opposite.
For my racing I need both torque and HP at higher rpm...

Here's what I have as the Gordon Blair formula, and it offers 4 alternative lengths for any given ambient air temperature.

Gordon Blair gives the following empirical formula for induction lengths (see: “Design and Simulation of Four-stroke Engines”). He maintains that it is accurate to about 3%.
The induction wave is reflected up to five times, and the equation for the length is:
L = (aC /N)
Where L = Induction length from valve head to end of bellmouth in mm.
a = reference speed of sound at 340 at 15 degrees C, 346 at 25 degrees C
C = Dimensionless intake ramming factor
* for first ramming peak C = 8900, second C= 6600, third C= 5150, fourth C= 4150.
N = rpm at which you want the torque improvement.