# Stroke

Pictured is a crank with rods and pistons. The diameter of the crank determines the stroke of your piston.

## What you do:

Choose a stroke that give you the power you want and the rpms (revolutions per minute) you want.

Factors to consider:

displacement = number of cylinders x 3.14159 x (bore / 2)^{2} x stroke

maximum rpm due to mass = 0.0056 x displacement^{2} - 8.8889 x ci + 11527

average piston speed in inches per minute = 2 x stroke x rpm

average piston speed in miles per hour = __2 x stroke x rpm x 60__

12 x 5280

air velocity through intake valve in feet per minute = __2.616 x 2 x stroke x rpm x 3.14159 x bore__^{2}

average open intake valve area x 12 x 4

This is a close up of a crank. From left to right are a rod journal, the main journal that gets fastened to the block and another rod journal.

Definitions:

displacement = how many cubic inches (in

^{3}) your engine is.

stroke = the distance the piston travels in the cylinder.

bore = the diameter of the cylinder.

rpm = revolutions per minute