Victory Product Design - BMW E46 323/325/328/330 Underdrive Pulleys - FREE Shipping. Underdrive Pulleys are simple in operation and work by reducing the rpm’s on the driven engine accessories. By driving these accessories slower, more horsepower is “made-free” to drive the wheels. While there might be slight variations in power increases from vehicle to vehicle, you will notice that the engine will rev quicker and be more responsive. Typical power ranges will vary from 5-11 hp. Our pulleys are engineered and designed by our own staff and are made using the latest CNC machines. Confirmation of our design has been proven with many daily driven miles being logged on our test vehicles under some of the most extreme hottest temperatures (Houston Summers). With our kit there is NO concern over high water temperatures or issues with power steering at low speeds due to underdriving the accessories. Our precision pulleys are made from 6061 T6 Billet Aluminum and feature our own proprietary stealth black hard anodized coating for long life. Lightening Slots are added to reduce the pulley weight and the rotational inertia which allows the pulleys to be accelerated quicker over heavier designs. WARNING: Certain manufactures that claim to be the originator of power pulleys for BMW’s state that the lower rotating inertia of the pulley makes no contribution to the power gain. Do not be misled by these incorrect statements. Power pulleys have been used for decades in the racing community to free up additional power and lighter, lower inertia pulleys allow an engine to accelerate quicker (over heavier designs) for the same reasons that a lightweight flywheel will allow an engine to rev quicker. The reasons for this is simple, less mass to accelerate. We believe we have designed one of the best underdrive pulley kits currently on the market and back it up with a Limited Lifetime Warranty. The kit comes complete with: Underdrive Water Pump Pulley, Underdrive Power Steering Pulley, Easy to Follow InstructionsLifetime Warranty.