This calculator is for entertainment value only.
Not to be used in place of real testing.

For a more accurate calculation try Larry Meaux's Pipe Max.
His program is excellent and will provide a lot of info.
Pipe Max

Estimate Throttle Blade Diameter For Individual Runner Intake
Enter Engine CID:
Enter Number of Cylinders:
Input CID and Cylinders, Please

This calculator shows what the butterfly of an individual runner intake (or motorcycle carb) is based on engine displacement.