This statement makes no sense. Since each piston is connected to the crankshaft via connecting rods this means that the RPM of the crankshaft represents the true RPM of the engine. Also since the up/down motion of the piston is transferred to the crankshaft and converted to a rotary torque it makes no sense to say the RPM of the pistons. Pistons do not have RPM but they do create RPM. Now you could compute the velocity of the pistons in the cylinders but I doubt this figure would mean much. If you want more horsepower you generally need either more air, more fuel, more displacement and thus more power, or a combination of those.
Like temperature gauges, magnetic sensors so you can see how much RPM each piston is running at?