How do the lengths of the bore and stroke affect the performance (power and torque), and general running characteristics (e.g. redline, noise etc) of a 4 cylinder engine?

Note: When asking this question, I mean engines with the same displacement, just different dimensions to get this displacement.

1 Answer 1


As the stroke increases the torque of the engine climbs because the connecting rod is attached further from the center-line of the crankshaft. This also limits the maximum RPM of the engine because there are increased friction losses due to increased speed of the piston at the same RPM when compared to an engine with less stroke. Further because of this increased speed piston experiences greater momentum which is harder to control at high RPM and requires stronger crank, connecting rods, piston pins, etc...

This decreased RPM capacity normally results in a lower horse power because power is a function of both torque and RPM. The exact opposite happens if an engine is destroked. The maximum RPM rises, the horse power rises all at the cost of bottom end torque.

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