| You maybe have heard of an old trick in the world of | | | | accessories. These are called underdrive pulleys. The |
| automotive performance that uses special pulleys to | | | | most obvious difference between an underdrive pulley |
| somehow pick up more horsepower from an | | | | and a standard pulley is that it has a smaller diameter. |
| otherwise stock motor. This might seem a little too | | | | This makes it so that the pulley does not turn as fast |
| good to be true, but believe it or not, it actually it is a | | | | as the stock pulley, meaning that less energy is used in |
| proven technique that you could apply to your engine | | | | the motion. More importantly, these pulleys are also |
| in order to increase performance. | | | | much lighter than a stock pulley, and the reduced mass |
| How does it work? Well, keep in mind that your engine | | | | makes them far easier to rotate. It is this last feature |
| is providing power to more than just the wheels of | | | | which gives you the biggest performance gains. |
| your car. For example, the alternator, the air | | | | Usually you can access about 3 to 5 free horsepower |
| conditioning compressor, and the power steering pump | | | | with these devices. |
| are all connected to the engine through a belt and | | | | I know what you are thinking if the pulleys are not |
| pulley system. Each of those accessories has a small | | | | spinning as fast as they used to, doesnt this mean that |
| pulley that gets rotated by your serpentine belt that big | | | | my accessories are not going to get the power that |
| belt located at the front of the engine. These pulleys | | | | they need to work properly? Yes and no. It is usually |
| take a small amount of horsepower from the engine in | | | | safe to underdrive your accessories by about 20 |
| order to keep turning and working while you are driving. | | | | percent. If you go below this point, you might start to |
| This is known as parasitic drag. | | | | notice issues like an alternator which does not |
| Now, normally this is not an issue. After all, the amount | | | | generate enough electricity to keep the engine running, |
| of energy it takes to turn two or three small pulleys is | | | | or a power steering pump that you have to fight |
| in the 5 to 7 horsepower range. No big deal, right? Well, | | | | against in order to turn the wheels. |
| when you are trying to squeeze every last drop of | | | | These issues, when they appear, usually occur only at |
| performance out of your engine, you should grab | | | | idle. This is why the 20 percent limit is recommended |
| whatever you can. If this horsepower is there for the | | | | on a street car. If you are running primarily on the track, |
| taking, why not take advantage? | | | | where you will see wide open throttle most of the |
| The way to eliminate a substantial portion of this | | | | time, then you can take the chance of running a more |
| parasitic drag is to install special pulleys that take less | | | | aggressive set of pulleys that will reduce parasitic drag |
| energy to turn yet are still capable of running your | | | | by a greater amount. |