Pulley kits are a great, easy way to free up horsepower from your BMW M4 engine. With underdrive pulley kits, your accessories (such as air conditioning, power steering, alternator, and water pump) are slowed down by installing slightly oversized pulleys with longer belts. The result is less parasitic drag and less rotational mass, especially when an underdrive BMW M4 crank pulley is installed. Power increases of 10-15 horsepower are not out of the norm for aftermarket pulley kits, so we think you'll agree that they're a worthwhile investment.

While pulley kits have sometimes been accused of slowing down BMW M4 engine accessories too much, the truth is that the majority of today's pulley kits' effectiveness is greatly dependent upon how the vehicle is driven. On a vehicle that sees a lot of stop-and-go traffic, it is possible that underdrive water pump and alternator pulleys made a few years ago would slow things down beyond usefulness, but most pulleys today are designed with a good compromise between performance and drivability. For performance applications, underdrive pulleys are of great help in preventing cooling system cavitation at high RPMs. Some BMW M4 pulley kit manufacturers even offer stock diameter pulleys for those who only want the benefits of a lighter pulley, which includes less rotational mass.

Q: What exactly is included in a pulley kit?
A: Pulley kits are car specific, and depend of whether you have power steering and/or air conditioning. The basic pulley set includes pulleys for power steering, alternator and air conditioning as needed, as sometimes come pulley belts (see the product description on our website to be sure).

Q: What are pulley kits? Why buy a pulley kit?
A: Pulleys are what drive your vehicles power steering, alternator and air conditioning unit. Belts attach to these pulleys and keep all the units running smoothly. By increasing the diameter of these pulleys, you slow down the power steering, alternator and air conditioning unit, reducing the amount of energy needed to drive them. Horsepower gains can be realized with a simple install package that has no recorded effect on emission levels. Beyond that, pulley kits often come in custom finishes, such as polished or anodized, and give your engine bay a clean custom look.

Q: How do you install a pulley kit?
A: Pulley kits are installed using hand tools. First remove your factory belts (this is a good time to buy replacements), and then remove the bolts to take your factory pulleys off. Replace them with the lightweight, larger diameter pulleys.