This will work for runner length and is not propreitary:
RL = 3E-07x^2 - 0.0067x + 44.808
RL = runner length
x = rpm
note: ^2 means squared
Remember, runner length is from the seat to the end of the air horn. The best way I have found to measure the length, just in the head is to form a wire along the floor from opening to seat. Measure it. Do the same to the roof. Add both together and divide by 2. You may want to do the same for the intake runners, or or injector air horns, or if using webers, to the end of their air horn. That is ideal length.
As for those spinners......paper weight? LOL!