A supplied crank is cut to customer's requirements, balanced, and polished. This modification is suitable for all 4-cylinder engines except those running substantial boost. Benefits are especially helpful (and even critical for sustained operation) at high rpms.
The primary reason to knife edge a crank is to improve its aerodynamic efficiency. This is done via carefully profiling the counter weights to cut vs. bash their way through the air and oil that's in the pan. This should follow the first step of using a windage tray and possibly a crank scraper setup. The less oil drags on the crank, the more free it can rev and transmit power to propel the car.
Secondarily, anybody that's revved a sportbikes knows that the throttle response is way beyond a street car engine. They pick up rpms so quickly because the ratio of engine output to engine mass is much higher. There is literally less engine weight for the engine to have to move around. The heaviest moving item in any engine is the crankshaft. So, strategically removing some mass means that more power gets to the wheels sooner and faster. With that said, lighter pistons and rods should be implemented before or at the same time the crank mass is reduced. A light crank with full weight rods/pistons will shake.
Note: Lead time: 3 - 4 weeks
Note2: This service is rendered upon a customer-supplied crank that may either be used or brand new. Given the number of heat cycles that a used crank has been through, there may be tensions built up within the crank due to metallurgical changes. This causes unavoidable warpage about 1.5% of the time according to our statistics. In such case, the crank must be reground and used with oversized main bearings. This service costs $150.