Cubic Inches


The HiPerMath equations are:

cubic inches = (number of cylinders)(3.14)(bore / 2)2(stroke)



maximum rpm due to mass = 0.0056(cubic inches)2 - 8.89(cubic inches) + 11527

engine weight = cubic inches + 100


Bore_istock

What you do:

Choose a stroke and bore that gives you the desired cubic inches of displacement.


Factors to consider:

1. The higher the ci (cubic inches or in3) displacement you have, the higher the torque. Bigger engines have more torque because they produce the power faster. They produce power faster because more air can be drawn or pushed in to an engine with large cylinders and a long stroke every revolution of the crank. Large ci engines produce power at a higher rate per rpm (revolutions per minute) than smaller engines.

2. The higher the ci displaced, the lower the maximum rpm. Engines with longer strokes and larger pistons have more mass rotating, so there is more stress on the crank. The crank can only handle so much stress, so rpm is limited.

3. Weight. Weight is always a factor in racing. Bigger engines are heavier and affect how a car handles. However, in drag racing, bigger is always better.

Definitions:

ci = cubic inches or in3
stroke = the distance the piston travels in the cylinder.
bore = the diameter of the cylinder.
rpm = revolutions per minute