Pulley is a simple machine which is used for changing the direction of force and moving the things up or down.
Whether your goal is looks, efficiency, or merely getting your engine running, pulleys are critical parts, and there are important factors that need to be considered when selecting them.
If you’re operating the engine with just the bare essentials of an alternator and a mechanical water-pump, there’s a pretty good chance everything will work properly, assuming you’re using stock pulleys designed to fit your engine. Things get a little more complicated when you add luxuries like power steering and air conditioning, and getting everything to line up and work properly can be a challenge.
So, if your engine and its related systems are stock and you use stock pulleys, everything should be OK. However, big problems can arise when you randomly mix and match pulleys in hopes that all the accessories will rotate at the proper rpm. To sort out a custom application, you have to understand the concept of pulley ratios. The ratio of any two drive accessories can be determined by dividing the diameter of the smaller pulley into the larger one. For example, if a 6-inch water-pump pulley is used in conjunction with a 7-inch crank pulley, the pulley ratio is 1.16:1. So for every 1,000 rpm the crank pulley spins, the water pump would rotate 1,116 times. Since the water pump spins at a faster rate than the crank, it’s said to be overdriven. Flop things around, and the water pump would spin slower than the crank and be underdriven. Underdrive pulley sets are often used to reduce the parasitic drag on the crankshaft to increase horsepower; however, altering the speed of the accessories can have adverse affects on the performance of the related systems, especially if they are already overburdened.
In addition to performance, looks and location are important too. There are several options. The cheapest way is to scour swap meets and junkyards. Another option is to call reputable pulley manufacturers and suppliers like Street & Performance, March Performance, Alan Grove Components, Zoops Products, Canton Racing Products, and Auto Specialties. These companies offer everything from simple factory-style replacements to complete serpentine conversions that can help optimize your current accessory system through various pulley diameters and configurations.
The only question is, with so many options available, which will you choose? Read on to find the ins and outs of various V-belt and serpentine pulley systems, along with what the various aftermarket manufacturers currently have available.