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Old 06-19-2008, 07:00 AM   #1
tim330i
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Join Date: Dec 1969
Location: Boston
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Forced Induction: Understanding Turbochargers, Intercoolers and Superchargers

Car racing, especially during the 80's, has had many influences on the automobile industry, including developing better ways to squeeze every ounce of performance out of engines and combustion elements. One of the most effective areas to "tweak" in automotive performance is to maximize the intake of air into the engine. The everyday "naturally aspirated" internal combustion engine relies on the negative pressure or vacuum that is caused by the pistons as each one moves down, sucking a mixture of air and fuel into its cylinder. As elegant and ingeniously simple as this method is, it leaves a lot of room for improvement.

Forced Induction:
Forced induction encompasses a variety of methods that can be employed to boost the performance of the internal combustion engine. In all cases, the goal of the device is to force more oxygen-laden air to mix with the fuel before being ignited. In the world of forced induction, turbochargers and superchargers dominate the field.

Turbochargers:
Turbochargers are air compressors linked to and driven by exhaust-powered turbines. It is the exhaust gases from the engine's combustion processes that drive the turbine's wheel. When the wheel of the turbine rotates, it concentrates the mass of the air entering the engine. The "boost" or pressure in psi, pounds per square inch inside the compressor, is proportional to the increase in power an engine will achieve.

Superchargers:
Supercharged cars step the aspiration process up by utilizing a compressor that is directly driven by a belt, chain or gear/shaft combo spun by the engine's crankshaft. Superchargers are often referred to as blowers and you will hear them when they engage - a droning, winding, humming sound is produced. The result, as with a turbocharger, is an increased amount of per-cylinder oxygen which is one of the 3 components needed to create combustion. The other two are a spark from the plugs and fuel (gasoline).

Intercoolers:
The Combined Gas Law is a mathematical law that states that compressing air raises its temperature. When a turbocharger or supercharger is used to increase engine power, the increased volume of oxygen entering the air intake manifold is less concentrated. This thinner air delivers less air and fuel mass to the engine. The colder the air, the more mass it has, and the more power it can deliver, thus the purpose for intercooling.

Aftermarket and Manufacturer Installed:
To increase power and performance, or to just increase fuel efficiency, devices such as turbochargers are being installed in today's production cars. The 2008 BMW 328i Coupe offers a naturally aspirated 3.0 Liter 6-cylinder engine which produces 230hp. For those who do not mind paying a few extra installments on their auto loan, the 2008 BMW 335i Coupe offers a twin-turbocharged version of the same engine which produces 300hp. Many production performance vehicles and luxury performance vehicles offer a turbocharged trim level with a significant horsepower uptick. For those who possess the funds and the motivation, aftermarket outlets are well-stocked with supercharger, turbo and intercooler kits to quench your thirst for power.
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