Enter the engine efficiency (VE), the CID, RPM, and speed into the calculator to determine the engine air intake diameter.

Engine Intake Diameter Formula

The following equation is used to calculate the Engine Intake Diameter.

D1 = SQRT ( VE * CID * RPM * 144 * 4 / (S * 88 * 3456*pi))
  • Where D1 is the engine intake diameter
  • VE is the engine efficiency
  • CID is the engine size
  • RPM is the rotations per minute
  • S is the speed (miles/hr)

What is an Engine Intake Diameter?


The engine intake diameter, also known as the inlet diameter or bore is the diameter of a cylinder at the point where the piston travels through the cylinder head into the combustion chamber.