[repsilat]

If they're only different by a constant factor, then both have the same interesting properties and neither is much more difficult to calculate than the other -- at least for sinusoids.

If something is proportional to one, it's naturally proportional to the other.

[uxp100]

Almost anyone on this website could answer better than me for this, was always weak in math, but I believe they differ by a constant factor for a sine, but for a more complex waveform they will not (well, the amount they vary by would be different for each waveform).

[lvh]

It's true that the factor between RMS vs peak-to-peak is different for e.g. a sine vs a sawtooth wave, but for other waveforms its still a constant (just a different one), and for this engine it should be just about a sine wave anyway.

[LeifCarrotson]

Circular motion about a crank produces a precise sinusoidal waveform.