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Why Adding Power by Boosting by a Turbocharger is a Worthy Upgrade

A turbocharger is simply a supercharger that is powered instead by a turbine in the exhaust stream. The first of these, dating to 1915, were referred to as “turbosuperchargers” and were employed on radial aircraft engines to boost their power in the thinner air found at higher altitudes.

A turbocharger uses the velocity and heat energy of the hot exhaust gases rushing out of an engine's cylinders to spin a turbine that drives an impeller which in turn compresses more air back into the engine. A supercharger also pumps additional air into the engine, but it is instead driven mechanically by the engine via a belt that runs off the crankshaft or, these days, by an electric motor.

The concept of forcing an engine more air than it would normally ingest, so that it can burn more fuel and produce more power. This additional intake air can be supplied by either a turbocharger or a supercharger. Both are air compressors, but they operate and perform very differently.

In that fashion, turbochargers capitalize on some of the "free" energy that would otherwise be completely lost in the exhaust. Driving the turbine does increase exhaust back-pressure, which exerts some load on the engine, but the net loss tends to be less by comparison with the direct mechanical load that driving a supercharger involves.

What are a Turbocharger’s Advantages?

  • Significant increase of horsepower
  • Power vs size: allows smaller engine displacements to produce much more power relative to their size. 
  • Better fuel economy: smaller engines use less fuel to idle, and have less rotary and reciprocating mass, which improves fuel economy. 
  • Higher efficiency: turbochargers run off energy that is typically lost in naturally aspirated and supercharged engines (exhaust gasses) and therefore the recovery of this energy improves the overall efficiency of the engine.

And because it has these benefits, there are also notable cons when you wish to go the boosted lifestyle.

Turbo Cons

  • Turbo lag: turbochargers, especially large turbochargers, take time to spool and provide a useful boost. 
  • Boost threshold: for traditional turbochargers, they are often sized for a certain RPM range where the exhaust gas flow is sufficient to provide an additional boost to the engine. Typically, they do not operate across as wide a range of RPMs as superchargers. 
  • Power surge: in some turbocharger applications, especially with larger turbochargers, reaching the boost threshold can lead to an almost instantaneous power surge, which could compromise tyre traction or cause some car instability.
  • Oil requirement: turbochargers get very hot and often tap into the oil supply of the engine. This calls for additional plumbing and is more demanding in terms of engine oil. Superchargers typically do not require lubricating engine oil.

How Much More Power Will My Engine Make?

Naturally aspirated engines operating at sea level get air at 14.7 psi, so if a turbo or supercharger adds 7 psi of boost to an engine, then the cylinders themselves are getting roughly 50 percent more air and should theoretically be able to produce about 50 percent more power.

But compressing intake air adds heat, which with the added pressure, increases the likelihood of engine-damaging pre-detonation or "ping," so the timing has to be retarded.

This can limit the amount of time the fuel has to completely burn and hence erodes some of the power gains. Most modern engines running turbos and/or superchargers also include intercoolers to help remove some of the heat added by the turbo or supercharger. In the end, the typical expectation is that adding 50 percent more air yields 30 to 40 percent more power.

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