A breakdown of turbos and superchargers that everyone can understand.
IT’s no secret that forced induction is a great way to increase the power of your muscle Mustang or fast Ford, but many of you may not know the secrets behind stuffing the cylinders with extra air, and why it can add so much power, even to an otherwise-stock engine.
The purpose of this article is to not only inform you as to how and why superchargers and turbochargers work, but to also teach you about both kinds of forced induction methods.
This Roush TVS is a typical...
This Roush TVS is a typical positive-displacement supercharger. It is designed to sit on top of a special intake plenum and force air directly into the engine through an integrated intercooler.
Positive-displacement superchargers,...
Positive-displacement superchargers, such as this Magnuson from Tork Tech, typically have a built-in bypass valve to relieve excess boost when the throttle is closed or under part-throttle cruise.
This is a front and rear view...
This is a front and rear view of a Twin-Screw Kenne Bell supercharger cutaway. Notice how the red rotor has convex (male) rotors, and the blue rotor has concave (female) rotors. Unlike a Roots-type supercharger (which has matching lobe-and-cavity rotors), the twin-screw compresses air between the rotors, rather than along the perimeter of the case of the supercharger.
What is forced induction?
Forced induction is the act of supplying a compressed air charge to the combustion chamber, beyond what can normally be drawn in by the natural induction process. Basically, the more air you can stuff in the cylinders, the more power you can potentially create (assuming you can also supply enough fuel and burn it efficiently).
Normal atmospheric pressure (one atmosphere) is considered to be 14.7 psi, though factors like weather (temperature and barometric pressure) and altitude play a role. Normally aspirated engines run on air that reaches the intake manifold by the downward movement of the pistons, creating a pressure drop inside the cylinders, which causes air to rush into the engine through the throttle body.
Pressure above one atmosphere is considered boost. This can only be achieved by forcing the air charge into the engine using a device such as a turbocharger or supercharger. Pressurized air, or boost, is measured in psi.
This is a front and rear view...
This is a front and rear view of a Twin-Screw Kenne Bell supercharger cutaway. Notice how the red rotor has convex (male) rotors, and the blue rotor has concave (female) rotors. Unlike a Roots-type supercharger (which has matching lobe-and-cavity rotors), the twin-screw compresses air between the rotors, rather than along the perimeter of the case of the supercharger.
Why is boost so popular?
Without even removing so much as a valve cover, turbo and supercharger kits can be installed on an otherwise-stock vehicle. These kits can increase power output by up to 100 percent or more. Most kits are competitively priced, relatively easy to install, and are typically upgradeable. On top of that, turbos and superchargers are a social statement. The fact that your Mustang is either supercharged or turbocharged boosts your social status, not only by making you look cool, but also by making your car sound cool. Whether it’s the whistle of a Vortech or ProCharger, the whine of a Kenne Bell or Eaton, or the snobby pssssshhh of a blow-off valve, forced induction systems are just plain cool.
There are countless other ways to add power to your fast Ford. And in the Mustang aftermarket, a consumer has more options for products than is possible to install on one car. Bolt-on items such as heads, camshafts, intake manifolds, and throttle bodies can help improve the volumetric efficiency of an engine, but a street engine will rarely achieve 100 percent volumetric efficiency—at least without boost.
Another way to increase power output is to increase displacement. This, however, requires the engine to be removed and either replaced with a larger displacement short-block, or rebuilt with a stroker crankshaft and/or bored to accept larger-diameter pistons. Either way, this process is time consuming and expensive.
Superchargers
Superchargers, otherwise known as blowers, are a form of compressor driven by the engine’s crankshaft (often with a belt) to turn an impeller or rotors, which compress air to create boost. Though there are nearly a dozen companies that manufacture them, superchargers can be categorized into two main types—positive displacement and centrifugal.
Positive Displacement
Positive-displacement superchargers are typically mounted to the top of an engine and integrated into the intake manifold. Because of their ability to pump at their maximum potential from the first revolution, they are great at making boost in the low-to-mid rpm range, and reaching maximum boost more quickly than centrifugal superchargers and turbochargers. The benefits are immediate power, and loads of torque.
Because of their simplicity, reliability, and few moving parts, they have been used in production vehicles such as the ’03-’04 SVT Cobra, ’99-’04 SVT Lightning, and ’07-and-up GT500. They are usually limited to about 25,000 rpm. Often, spinning them faster results in loss of efficiency.