Engine boosting is a process that uses a device, typically a turbocharger or supercharger, to force more air into an engine's combustion chambers than would naturally occur. This process is also known as forced induction.
Understanding Forced Induction
At its core, boosting is about increasing the density of the air entering the engine. A naturally aspirated engine relies on atmospheric pressure and the downward movement of the pistons to draw air in. However, a boosted engine actively pushes or pulls air into the cylinders under pressure.
The term "boost" is often used as shorthand for the positive combustion chamber pressure created by a turbocharger or supercharger. The primary point of this process is to direct additional air into the engine.
Why Boost an Engine?
By forcing more air into the cylinders, an engine can burn more fuel efficiently in each combustion cycle. This results in:
- Increased Power Output: The primary goal of boosting is typically to significantly increase the engine's horsepower and torque without increasing its displacement (size).
- Improved Efficiency (in some cases): Smaller displacement engines can be boosted to produce power comparable to larger engines, potentially leading to better fuel economy under light load conditions.
- Enhanced Performance: Boosted engines often offer better acceleration and responsiveness.
How Boosting Works: Turbochargers vs. Superchargers
The two main types of forced induction systems are turbochargers and superchargers. Both compress air, but they achieve this compression differently.
| Feature | Turbocharger | Supercharger |
|---|---|---|
| Power Source | Engine exhaust gases | Engine crankshaft via a belt or gears |
| Mechanism | Turbine spins a compressor wheel | Mechanical compressor (e.g., roots, screw, centrifugal) |
| Lag | Can have "turbo lag" at low RPM | Provides instant boost |
| Efficiency | Generally more efficient at higher RPM | Less efficient due to parasitic drag on the engine |
| Heat | Produces more heat due to exhaust energy | Generally produces less heat than turbos |
Turbochargers
A turbocharger consists of two main parts: a turbine and a compressor, connected by a shaft. The turbine is driven by the engine's exhaust gases, which would otherwise be wasted energy. As the turbine spins, it drives the compressor, which draws in ambient air, compresses it, and forces it into the engine's intake manifold.
- Benefit: Recycles waste energy (exhaust gas).
- Challenge: Can suffer from turbo lag, a delay between pressing the accelerator and the boost kicking in, as the exhaust flow needs to build up to spin the turbine.
Superchargers
A supercharger is mechanically driven, typically by a belt connected to the engine's crankshaft. It uses various types of compressors (like Roots, twin-screw, or centrifugal) to compress intake air and push it into the engine.
- Benefit: Provides instant boost as soon as the engine is running.
- Challenge: Consumes some of the engine's power to operate (parasitic loss).
In Summary
Engine boosting, or forced induction, is a technique using devices like turbochargers or superchargers to compress the air entering an engine. This compression creates positive combustion chamber pressure – the "boost" – allowing more air and fuel to be burned, resulting in increased power and performance. It's a key technology in modern engines aiming for a balance of power, size, and efficiency.
