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    Producing Quality Computer Tools for Racers and Engine Builders since 1986






Piston Position

What is Piston Position and how does it affect engine performance?

Piston position is a measure of how far the piston is down the bore from it's TDC (top dead center) position.  Piston Position can be determined from the crank angle from Top Dead Center, knowing the Stroke of the engine, Length of the Connecting Rod and the angle of the Crank. As the Crank Shaft rotates a certain degree, the Piston moves a certain distance from Top Dead Center.  This is primarily determined by the engine's Rod/Stroke Ratio, which is a term many engine builders use to characterize certain types of motors.

Most people consider Piston Position when thinking about Valve Clearance. By knowing the Piston Position and the Valve Position at different crank angle degrees, one can verify that the Piston and Valves don't hit each other while running in the engine. This will prevent a catastrophic engine failure caused by Piston/Valve interference.

Piston Position also has to do with when the Exhaust and Intake Valves open and close to maximize the performance of the engine. Small modifications to the Cam Profile can greatly change the performance of an engine.

How piston position changes determines how cylinder volume is changing with crank angle.  This can have some affect on how the cylinder pressure changes as the piston goes through it's entire cycle.  Again, this is determined by the engine's Rod/Stroke Ratio.  


Programs that take Piston Position into account

We have 3 programs that work with Rod/Stroke Ratio and Piston Position when conducting Engine Simulation: Engine Analyzer v3.4, Engine Analyzer Plus v3.4 and Engine Analyzer Pro v3.9.  The Engine Analyzer Plus v3.4 and Engine Analyzer Pro v3.9 also will estimate Piston to Valve Clearance from Piston Position and other factors.  

We have 1 other program that takes the Piston Position into account when making calculations. Compression Ratio Calculator v2.3 calculates allows you to change the Rod/Stroke Ratio to help figure out the Dynamic Compression Ratio.