Underdrive Power Pulleys work to 'free up' horsepower. Any accessory that spins from the main drive belt is using up power. That's power that could otherwise be used to move the car. By giving some of that power back to the engine, you can make the car faster! It's like FREE HORSEPOWER! Turner measured 10.7 whp at 6960 rpm and 8.1 lb-ft of torque at 5550 on a 1995 M3.
Underdrive pulleys for your BMW will slow down engine-mounted accessories - the water pump, power steering pump, and alternator*. These systems contribute to 'parasitic losses' - power lost from what the engine could produce if it did not have these systems. Since less energy is used to move them, that power is transferred back to the engine and used to propel the car. Turner Motorsport pulleys give a 10-20% reduction in rotation, releasing up to 11hp on most six-cylinder engines. There's also a small but noticeable improvement in throttle response too! There has been extensive testing and development work, both on and off the track, to ensure that the accessory systems function as they should. On Turner Motorsport Racing pulley kits they actually underdrive certain components more so they feel their Street pulleys are an ideal compromise between power/torque gains, reliability, and system performance. Turner Motorsport's pulley kits have been on the market for over ten years, and used in all of their own cars, with zero component failures related to their use.
Turner Motorsport pulleys are made from T-6061 aluminum and finished in a durable black hard anodize that is very resistant to wear, chemical exposure, and heat. They designed their pulleys to look similar to the factory parts but also to be stronger and, in most cases, slightly lighter too. For example, a Turner alternator pulley is more than half the weight of the stock steel pulley! With their hardcoat aluminum you will never have to worry about a serious failure of a stock plastic pulley. A 'stealth' approach to aesthetics was Turner's goal and they let the results speak for the pulley design. Installation is straight forward and easy with simple hand tools. Removal of the fan is required for access to the front of the engine. Total install time for a 3-piece pulley set should be around 1.5 hours. A new longer belt is included and we also recommend replacing the separate A/C belt, belt tensioners, and the guide and deflection pulleys at the same time.