Piston Speed: By calculating piston speed (in feet per minute) we can estimate what our redline should be. Piston speed is directly related to the stroke of the engine. The shorter the stroke, the higher the engine can safely rev. The formula for piston speed is: Stroke (in inches) x RPM (the rpm you are checking piston speed for) x .166 (a constant) For example: We are building an engine with a stroke of 3.5", that revs to 6000 rpm. What is the piston speed at 6000 rpm? 3.5" (stroke) x 6000 (rpm) x .166 (the constant) = 3486 (fpm) feet per minute. In general the following table will guide you on what your maximum piston speed should be. You can rev the engine higher but wear and longevity will be reduce. 3000 fpm = Stock engine. 4000 fpm = Engine with good quality connecting rods, good quality rod bolts, and other appropriate supporting mods. 5000 fpm = Formula 1 engine. Horsepower: Horsepower is a measure of work. If we know the amount of torque produced at a given RPM, we can calculate horsepower. Horsepower = Torque x RPM / 5250 For example: An engine that makes 200 lb/ft('pound-feet') of torque at 7500 RPM will make 286 HP 200 (lb/ft or torque) times 7500 (RPM) = 286 horsepower Web site contents © Copyright Scott Tucker 2011, All rights reserved.