Turbocharger (FAQ)

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Contents 1 Intro 2 General 2.1 What is a Turbocharger? 2.2 Why is a turbocharger different than a supercharger? 2.3 Common Turbocharger myths

Intro

A turbocharger uses a turbine that is driven by the hot, expanding exhaust system stream to power a centrifugal compressor which forces air into the engine. Because a turbo is actually driven by wasted energy, there is no loss from the engine to power the turbo. However, because the system is run off the exhaust, it may take some time before the exhaust level builds up to a sufficient level to run the turbo charger. This delay in power delivery is called "Turbo Lag" and can lead to a significant pause between stepping on the gas and the feel of additional power. Furthermore, turbos often require cool down periods after use (meaning you have to let the car idle for a few minutes (!) everytime you want to shut the engine off, or else reduce the life of your turbo-charger, which only last 7-10 years anyway. More modern turbo charger designs have allowed turbos to slowly spin down even after the engine has been shut off and are more durable than older designs.

Most turbos use intercoolers, wastegates and compressor bypass valves (blow off valves) to help provide more useable power. An intercooler is a heat exchanger that is used to cool the air heated by the turbocharger's compressor. Therefore, the intercooler can significantly boost power because the cooler air it provides is more dense than the hot air straight out of the turbo. An intercooler also takes thermal load off of the engine by cooling the intake air. A wastegate is designed to regulate boost pressure, and is simply a valve in the exhaust system that allows some of the exhaust to bypass the the turbo when it is not needed. The Bypass valve is a valve between the throttle and the turbo that vents extra boost pressure. When this valve vents to the outside air, it is called a blow off valve, and when it vents back into the inlet of the turbo, it is called a compressor bypass valve.

A turbocharged engine's compression ratio must be lowered by using a lower compression piston, since an excessive amount of pressure will wear on the piston, connecting rods, and crankshaft, and destroy the engine. All of these parts then, as well as the transmission, must be strengthened on a turbocharged engine or it will be torn apart by the increased horsepower.

• Advantages: Greater peak power
• Disadvantages: Lag in power delivery, long-term durability, cold-start emissions
• Applications: Recommended for high RPM applications (i.e. I4s)

General

What is a Turbocharger?

Technically, a turbocharger is a compressor powered from the waste exhaust gas expelled by an internal combustion engine. This compressor pumps additional volumes of air into an engine, and when combined with additional fuel volumes, forces it to mimic a larger displacement engine; therefore creating more power.

Why is a turbocharger different than a supercharger?

The primary difference between centrifugal superchargers and turbochargers is the method in which they receive power. A supercharger is a powered from the engine drive belt in a similar fashion to the air conditioner. A turbocharger uses otherwise wasted exhaust gas to spin an impeller which in turn drives a compressor and creates large volumes of gas (air in this case).

Common Turbocharger myths

• Turbochargers all have lag and superchargers are way better!

First: All turbochargers have lag, whether they be run of the mill types used on a tractor trailer or of the semi exotic variable geometry ceramic vane variety. But in the shocker of the century all superchargers have lag as well. Lag is a function of the laws of physics and no matter what variety of forced induction you go with it will be there. On the other hand modern turbo technologies, specially those dealing with material science and aerodynamics, have advanced to the point where a well designed street setup will have lag that is order of magnitudes smaller than previous generations of turbocharged vehicles.

Second: Lag is the time delay between the time you stab the gas and the time in which the turbocharger spools to its limited maximum boost. Most people, when they speak of lag, are referring to boost threshold. Boost threshold is the time it takes for the turbo to produce any tangible boost. As with lag boost, threshold has been improved over the years and a modern, well designed system makes it much less of an annoyance than it once was.

• Turbochargers are guaranteed to blow up your engine!

If you need more power just keep turning up the boost, otherwise known as the free energy effect.