Small Engine Performance Jesse Morris Spring 2002 Virginia Tech Edited by CTAE Resource Network March 2011

Performance Objective Students will be able to describe all performance applications that are used in a small engine setting.

Enabling Objectives Explain small engine displacement. Interpret small engine force & pressure. Describe work and energy principles. Explain horsepower and how it is derived. Describe small engine torque.

Small Engine Displacement Displacement is the total volume space increase in the cylinder as the piston moves from the top to the bottom of its stroke.

Force Force is the pushing or pulling of one body on another. The entire small engine design is based on force. Ex: The crankshaft pushes and pulls the piston. Force is also achieved by the rotation of the crankshaft. Force is often measured in pounds, ounces, and grams.

Small Engine Pressure Pressure is a standardized measure of force, it is force per given unit of area Pressure is measured in P.S.I.(pounds per square inch) PSI= Force Area Ex. PSI can be determined by the amount of combustion in the combustion chamber

Work & Energy Work = Force x Distance – Work is usually expressed in feet/pounds. – The work of a small engine varies in different applications. Energy = the capacity to perform work. – Small engines change stored energy of gasoline into mechanical power.

Horsepower The rate of power output by a small engine Engine horsepower can be derived by dividing the total rate of work by 550 (ft lbs. per sec) 3.5, 3.75, 6 are all common HP #’s in small engines

Horsepower Brake HP is the usable horsepower delivered at the crankshaft. An engine’s rated horsepower is usually 80% of its maximum brake horsepower. (10 hp motor is rated at 8 hp)

Torque Torque is the turning force that is created by the crankshaft. Torque curves vary at different engine speeds. The larger the horsepower motor the more torque it will have.

Key Points Displacement Horsepower Work & Energy Displacement Pressure Force