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# Tech Tips/Calculators

## Engine Displacement Calculator

 Bore (Inches): Stroke (Inches): Number of Cylinders: cubic inches cubic centimetres

### Stroke or No Stroke?

Many believe that cubes equal horsepower, and that’s true, though long strokes are not as effective at pure horsepower production as large bores are.

#### Why?

Horsepower is a function of torque [hp=(lb-ft x rpm)/5,252], and stroke alone is rpm limiting. Stroking increases piston speed (a 3.480 stoke engine at 6500 rpm moves the piston at 3,770 feet per second; a 3.750 stroke does it at 4,063 fps) and the fast piston speed reduces the time available for cylinder filling at high rpm. Therefore, the torque production drops off at a greater rate than rpm increases, and horsepower production is cut short. Strokers can be made into high-rpm race engines, but there’s a greater cost in heads (to flow with less pressure drop at high rpm), valvetrain (to survive the more aggressive profiles required), and lightweight internal components. On a street engine, lengthening the stroke (beyond a certain point) and changing nothing else tends to favor low-end torque over high-end horsepower. That’s less true in the case of very small engines such as 289 fords, 273 mopars and 283 chevys; in witch case the sheer increase in displacement is worth power everywhere.