A supercharger is basically a large pump that compresses and forces air into your vehicle’s engine to create additional horsepower. Because they can easily and affordably generate reliable horsepower, they are not only becoming popular choices for the aftermarket crowd, but also in OEM applications. We decided to find out where superchargers come from, how they work, what types are available, and which one is right for you.

The beginning of Superchargers dates back to 1860 when an Indiana man named Mr. Francis Roots created an industrial two-rotor “air engine.” This is where all the roots-style superchargers we see today started. Shortly thereafter, a German engineer named Kriggr invented twin rotating shafts that both compressed and pumped air. This is the same basic technology that can be found under the hood of many of today’s cars, known as the Twin-Screw Supercharger. But it wasn’t until 1900 that Gottlieb Daimler (sound familiar?) got a patent for a pump that would help move larger amounts of air and fuel into a vehicle’s cylinders. Although it did not have its modern name at the time, this is what many consider to be the birth of the automotive supercharger. Shortly after that, Superchargers started showing up on race cars. Lee Chadwick was one of the first American racers to use a centrifugal supercharger in competitive racing with successful results. World War I military aircraft later used Superchargers to overcome a lack of horsepower at high altitudes. By 1921, Mercedes was making Supercharged cars and the Supercharger era had begun.

At a very high level, there are three types of superchargers: mechanically actuated, pressure wave, and exhaust actuated. The pressure wave supercharger is rarely used in the automotive world, so we’ll leave that out of this discussion. The ever-popular exhaust-actuated supercharger, also known as a turbocharger, is increasingly used in today’s high-performance market. Since most people put this type of SuperCharger into its own category, we’ll also put it aside for now and focus on the mechanically powered versions for today. These are the blowers we think of when we hear the term Supercharger. They can also be divided into different categories: roots, double screw and centrifugal. They all have their pros and cons, and hopefully, after reading this article, you can decide which one works best for you.

Unlike turbochargers that work with the exhaust gases coming out, superchargers are mounted on the engine and are driven by a pulley that comes off the crankshaft. Air enters the supercharger and is then compressed before being discharged into the engine intake. This raises the density of the air charge before it enters the cylinders. As RPMs increase and the crankshaft begins to spin faster, so do the Supercharger’s impellers, forcing more air into the engine and creating Boost. Boost is created when air is forced into the engine rather than into the intake and is measured in PSI (pounds per square inch). The more boost that is created, the denser the air charge in the engine’s combustion chamber, allowing the engine to burn more fuel, resulting in more horsepower. If a car produces 6 pounds of thrust, it means that it is generating an additional 6 pounds of pressure above atmospheric pressure at that elevation. Atmospheric pressure is 14.7 psi at sea level. As many of you know, cars run best around sea level as opposed to high elevations. This is because the air begins to thin out as you go higher and becomes less densely packed with molecules. Superchargers provide power only at full throttle and therefore do not affect engine reliability under normal driving conditions.

One problem with superchargers is that because they spin at such a high speed, they also produce a lot of heat. Some companies have overcome this hurdle by taking advantage of the vehicle’s oil pan to lubricate the gears inside the supercharger’s main unit to minimize heat and friction. Others use internal belts or self-contained main units where the oil never needs to be changed. The air itself also gets hotter because you’re condensing it. Intercoolers are often used to cool the air and create a denser air charge. An intercooler is much like a car radiator. Two common types of intercoolers are Air-To-Air, which uses outside air to cool the air that has just passed through the Supercharger, and Air-To-Water, which forces air through a heat exchanger that is cooled by Water. Intercoolers are not always required, but are usually found in applications that produce higher levels of boost.

Another term you’ll hear commonly among Supercharger conversations is bypass valve. When a supercharger is trying to force air into the engine, but the throttle shaft is closed, it creates a situation called compressor surge. This can happen during deceleration or when the driver is between gears. When the Supercharger is trying to force air into a closed throttle body, and the pressure inside the throttle body is greater than the pressure created by the Supercharger, the air tries to force itself back into the compressor. When this happens, pressure inside the throttle body is released and the compressor forces air back through the supercharger and then back into the throttle body, creating a loop. This is where a bypass valve comes into play. It is actuated by inlet vacuum and then releases excess pressure to atmosphere (relief valve) or back through the compressor.

Most cars today don’t come with a fuel system that handles the power produced by a supercharger. More air means more fuel, so you’ll need to make sure you have a proper fuel system before installing one of these. Your ignition system is another area that needs to be considered. The ignition timing can be advanced or retarded, causing the spark to fire earlier or later. Many Supercharger kits delay timing to prevent detonation. This lowers peak cylinder pressures and temperatures and moves away from the detonation threshold. On some of the newer computer controlled vehicles, a Dyno-Tune by a professional tuner may be required to get your car running properly.

Most Superchargers sold today are Centrifugal Superchargers. These are Internal Compression Superchargers, meaning they create the boost (compresses the air) inside the main unit before forcing it into the engine intake. Its drivers are turned by an external pulley that is usually driven from the accessory belt. This allows you to change the size of the pulley and control the speed at which the Superchargers impellers rotate. By switching to a smaller pulley, you are essentially adding more momentum. An advantage to this style of blower is that because it has a limited number of moving parts, they are generally more reliable than other units. They also produce less heat than other style superchargers and are capable of producing more boost. The only downside is that it must spin at a high speed to generate a significant amount of thrust, and therefore only makes power at higher RPMs. It is common to start seeing a boost at 3000 RPM and for it to increase along with the RPM. These are great options for non-street cars that don’t normally care about low RPM. That’s not to say they aren’t a great option for street vehicles.

Roots Style and Twin Screw blowers are external compression superchargers. Both are also positive displacement superchargers, meaning it moves a fixed volume of air per rotation. The Roots style has two counter-rotating lobes that trap incoming air and move it around the outer casing of the lobes before releasing it out the bottom through an exhaust port. These blowers are very capable of generating large amounts of boost at lower RPM and making incredible low to mid range power. The main disadvantage of this style of blower is that they generate a lot of heat. An intercooler is almost always necessary in a roots setup.

The Twin Screw Supercharger is very similar in appearance to the Roots Style blower. One major difference in design is that the Twin Screw style has two rotors (screws) that rotate toward each other. The two screws engage and draw in air to compress it and expel it towards the engine. Due to the fact that compression occurs inside the Supercharger, it produces much less heat than a roots blower (and not much less than a centrifugal). The tolerances between the two bolts are very tight, resulting in the ability to create boost at low RPMs, much more than Roots or Centrifugal. Another advantage it has over the Roots style is that the two screws don’t actually touch each other, so there are virtually no wearing parts to replace. The main disadvantage of this style is that, due to its internal compression ratio, it compresses air even when not sending drive to the engine. They have internal bypass valves to release pressure, but due to the fact that it takes energy to create that pressure in the first place, it draws more power from the engine while not under pressure compared to the other blowers.