The Beginner's Guide to Forced Induction

October 31, 2012

While there are many different ways to go about modifying your engine for increased performance, few beat the power per dollar ratio that forced induction can offer. Unlike naturally aspirated engines which ingest air that is pressurized only by natural atmospheric pressure, forced induction methods such as the use of a Supercharger or Turbocharger increase power by artificially pressurizing air, and forcing it into the engine. All things equal, this increased air when mixed with additional fuel means vastly larger amounts of power. While turbochargers and superchargers both increase power through this method, the actual ways they go about it are substantially different.

Superchargers

Superchargers generally use pulley systems that use the crank pulley’s rotation to spin their compressors. It is because of this method of turning the compressor, that superchargers tend to amplify an engine’s power band, in essence taking its original power delivery and increasing it. Superchargers generally replace the intake manifold on an engine, and tend to run at lower boost pressures. Increases in boost pressure are accomplished via the fitting of smaller compressor pulleys, which spin the compressor faster for a given engine speed.

Superchargers tend to be more reliable and easier to install than turbochargers, due to the fact that they generate their biggest power gains in areas where the engine is already designed to make peak power. Because of this gradual power delivery, engine stresses are more gentle and easier to manage, which translates to greatly reliability and better drivability due to the absence of turbo-lag.

Turbochargers

Turbochargers, unlike Superchargers, use exhaust flow to power their compressors. Exhaust gas exiting the engine blows past the turbocharger’s turbine, which causes it to spin. The turbine is attached to the compressor by a shaft, so as the turbine spins, so does the compressor. Air is drawn into the compressor, compressed and then sent into the engine itself.

Because the turbocharger is driven solely by exhaust gas, the size of the turbine, the amount of exhaust gas present, and profile of the turbine and compressor blades all have significant impact on their ideal operating speeds. Given these intricate details, turbochargers tend to be tricky to optimize. A larger turbocharger designed for high rpm operation will generally tend to take more time to spin up to speed, which is felt as a lag in power known as turbo lag. Smaller turbochargers in contrast, can be brought up to speed very quickly. Though their high rpm performance tends to suffer, as does the maximum boost pressure they can generate. Ideal performance is generally found by striking the best compromise between these two extremes. It should be noted however, that because of a turbocharger’s potential for sudden, and potentially violent power delivery, stresses on the engine tend to be more severe than those seen in supercharged or naturally aspirated engines. This can lead to reliability concerns if proper restraint is not exhibited during use.

Turbochargers and Superchargers are key ingredients for power, but their delivery couldn’t be more different. While each has its own upsides and downsides, if power is what you are after, neither is likely to disappoint.

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