[v8klla]

If we are to trust that Fluidampr and ATI know what they're doing (and I do) then there would definitely be some adverse affects when using a crankshaft pulley. A lighter weight pulley will free up some horsepower, but it will adversely affect the longevity of your engine bearings. When, if ever, will a failure occur from this is the question, but is it really worth the risk?

From Fluidampr:

Each time the air/fuel mixture inside a cylinder is ignited, the combustion that occurs creates a torque spike that is applied to the crankshaft through the piston and rod. This torque spike is so severe that it not only turns the crankshaft, it actually twists the crankshaft ahead of its normal rotation and then the crankshaft rebounds. This twisting action is known as torsional vibration. When these torque spikes and forces get into phase with the natural frequency, critical torsional harmonic vibrations occur and can be seriously destructive to the bearings and the crankshaft. Dampers are designed to control those destructive vibrations.