Spring 2003 Forward to a Friend

and images of exotic, high-performance race cars may spring to mind. While a turbocharger can deliver impressive, high-end engine performance and acceleration (as in the world-class WRX), it also can improve the everyday, around-town performance of almost any vehicle while still providing efficient, economical operation.

An internal-combustion engine requires both fuel (such as gasoline) and air to operate. An engine’s performance is directly related to how much fuel and air it can take in and combust in its cylinders during operation – the greater the amount of air and fuel, the greater the engine’s performance.

A centrifugal turbocharger (turbo for short) increases the power of an internal-combustion engine by pumping air into its combustion chambers at higher-than-normal pressures.
A turbocharger forces air into the engine’s intake manifold. This creates a denser air/fuel mixture, resulting in higher engine power output. With a turbocharger, a smaller engine can provide the power of a larger engine without sacrificing efficiency, size, or weight. Best of all, a turbocharger doesn’t use any engine power to operate – it’s powered by the engine’s exhaust gasses, which would normally go to waste.

A turbocharger unit contains two fans. The fans are encased in separate chambers, but are mounted on opposite ends of a common shaft. The engine exhaust flows through one of the chambers past one of the fans (called the turbine), causing it to turn and rotate the shaft. The second fan on the opposite side of the shaft (called the compressor) is in a chamber mounted in the engine’s intake system. When the second fan turns, it compresses the air entering the engine’s air intake manifold. This “boost” of intake air works to improve the engine’s performance.

An intercooler system is often used when a turbocharger is installed on an engine. An intercooler cools the air compressed by the turbocharger before it enters the intake manifold. Why? As the incoming air is compressed by the turbocharger, its temperature increases, making it less dense and less effective for combustion. Mounted between the turbocharger and the intake manifold, the intercooler – essentially a small radiator – removes the heat from the air, increasing its density and improving its effectiveness before combustion.

The amount of turbocharger boost that’s delivered to the engine is regulated by the system’s wastegate. When the desired level of turbo boost is reached, the wastegate bypasses excess exhaust gasses around the turbine wheel. The wastegate’s operation is controlled electronically by the vehicle’s engine control module (ECM).

In the early 1980s when turbochargers started to become commonplace on production passenger cars, drivers often complained of a lack of turbocharger response at low speeds – a condition referred to as turbo lag. At low speeds, an engine produces very little exhaust gas, and consequently the turbocharger has very little to power it. When drivers stepped on the accelerator, it would take a few seconds for the increasing exhaust gasses to “spool up” the turbocharger to the point where it would produce a noticeable amount of power.
Engineers have essentially eliminated turbo lag through improved turbocharger design and the use of more effective computer-controlled engine management systems. The lopsided, all-or-nothing performance once provided by turbochargers is a thing of the past. Current turbocharging systems are carefully tailored to provide smooth power delivery and lower exhaust emissions at all engine operating speeds and driving conditions. It’s an effective, efficient way to improve your vehicle’s performance.

Both turbochargers and superchargers compress air entering an engine’s intake manifold to help increase power. While a turbocharger is powered by the energy in the engine’s exhaust stream, a supercharger is directly connected to the engine’s crankshaft via a belt, chain, or gears. With this direct connection to the engine, a supercharger requires the engine to work a little harder, and consequently, use more fuel. The increased engine output the supercharger provides makes up for the extra power it requires, but essentially superchargers are less efficient than turbochargers.