At low rpm, the engine has to work harder to produce the same amount of power as it does at high rpm. This is because the pistons have to move a longer distance in the cylinders at low rpm than they do at high rpm. The increased piston travel time means that the engine has to generate more torque, which puts more stress on the engine's components.
In contrast, at high rpm, the pistons have to move a shorter distance in the cylinders, which means that the engine has to generate less torque. This puts less stress on the engine's components and makes the engine more efficient.
