However, there are limits to which weight can be removed, particularly when longevity is a concern. To understand the environment in which a crankshaft must operate, consider the following in ultra-slow motion. Based on its inertial characteristics, each firing impulse must be absorbed by the crank, even as rotational torque is produced. This deflection of the crankshaft tends to "wrap up" the throw in question, after which it "rebounds" in a direction that is opposite to its rotation. This damped oscillation continues until the next firing impulse is delivered to the same throw. Meanwhile, other firing impulses are received by other throws on the crank, creating a highly complex system of rotational stresses comprised of both compressive and elongational loadings, all of which suggest caution and careful thought when attempting to reduce a given crank's rotational MOI
Over the years, we've seen data gathered using in-cylinder pressure measurement (Engine Cycle Analysis) that qualified the amount of torsional deflection (from the front to back of an engine) for both crankshaft and camshaft operation. Under conditions that allow an abnormal amount of such deflection, it's possible that cylinders toward the rear of an engine are operating on different crank and cam angles than cylinders in the front. It doesn't require much imagination to see how this could affect power optimization from conventional thinking that excludes such a phenomenon.