Many of the tips found in our fuel economy section also increase horsepower. However this modification is not one of them. Superchargers are devices similar to turbo chargers in that they compress air to feed into the motor for increased horsepower and torque. The difference lies in their method of operation, efficiency, and cost. A supercharger generally uses a belt driven system which spins an impeller specifically designed to compress air through a length of volume that is larger at the inlet and smaller at the outlet. The end effect of this is to end up with a volume of air that has a higher density then ambient air. More fuel can then be added to the additional oxygen to create more power through combustion. Several different types of superchargers exist.
Roots Type Supercharger
A Roots type supercharger uses lobes that mesh together much like gears do. As the multiple lobes spin, intertwined within each other they push sections of air on top of each other creating the supercharged effect. These superchargers have been around the longest as they were the first to be invented. They typically are large, and seen sticking out of the hoods of muscle cars. However they are not as efficient as the other types and usually weigh more as well.
Twin Screw Superchargers
Twin screw superchargers work much the same way as the roots type units. However the intermeshing lobes that they use are a bit different and more efficient. The area where the air is trapped reduces its size in volume as the air moves through the gears. This compresses the air in addition to stacking it like in a roots type supercharger, thus creating more power and efficiency.
These are the most popular and modern supercharger types. They are found most commonly in modern day vehicles that employ supercharger technology. Centrifugal superchargers are the most efficient and lightest units. They can typically increase horsepower and torque anywhere between 20 to 40+%. Centrifugal chargers use spinning impellers to attract air into the device. The impellers look similar to smaller versions of jet engine turbine blades and they can spin up to 65,000 rpm in some cases! After running through the impellers the high velocity air contacts a series of radially running flat or curved plates called vanes which help reduce the super high velocity of the air but increase pressure.
Fuel Economy Drawbacks
Superchargers are phenomenal at increasing horsepower and torque. However this usually comes at a cost: reduced fuel economy. In order to take advantage of the extra oxygen in the fuel mixture, quite a bit of additional fuel must be added as well. Usually this comes in the form of a higher capacity fuel pump, fuel pressure regulator, and set of injectors. At certain high supercharger rpms the added fuel necessary for proper combustion can cut gas mileage in half. So this mod is not recommended if you have a fuel economy budget in mind.
Prices of superchargers can range into the several thousand dollars as well. So they can be costly ventures for the automobile enthusiast.
Additional Proes and Cons
Although supercharger technology has distinct advantages to turbochargers they come with a few drawbacks. There is a characteristic “supercharger whine” associated with the centrifugal superchargers, the consequence of spinning an impeller at tens of thousands of rpm. This whine typically increases with increasing engine rpm and can be considered annoying to many people. Also because the supercharger is driven by a belt attached to the crankshaft of the vehicle, it robs some of the vehicle’s original power to spin the impeller, unlike a turbocharger which uses the vehicle’s exhaust gas to spin its impeller.
One of the pros of superchargers compared to turbos is the lack of lag time. Lag time refers to the inability of a turbo’s blades to spin to proper operating rpm quickly. It usually takes a higher rpm and more exhaust flow to get a turbocharger spinning properly. Because a supercharger is belt driven this is not a problem, and your horsepower is available to you at a lower rpm with a quicker response time than with a turbo.