Engines are fundamentally air pumps. The more air you can get into an engine, the bigger the combustion and the more power you can extract. Forced induction is the method of forcing more air into an engine beyond what it can naturally aspirate. In this article, we’ll explore the two main forms of forced induction: turbochargers and superchargers.
Turbochargers: Power from Waste
Turbochargers harness the energy from exhaust gases that would otherwise be wasted. Let’s look at the core components that make this magic happen:
Core Components
- Turbine Wheel (Hot Side): Located in the exhaust stream, this wheel is spun by the force of exhaust gases exiting the engine.
- Compressor Wheel (Cold Side): Connected to the turbine wheel by a shaft, this wheel compresses incoming air and forces it into the intake manifold.
- CHRA (Center Housing Rotating Assembly): Contains the shaft that connects both wheels and includes bearings that support the rotating assembly.
The Physics
Exhaust gas exits the engine at high velocity and pressure, spinning the turbine wheel. This rotation is transferred through the shaft to spin the compressor wheel at incredibly high speeds (up to 150,000+ RPM). The compressor wheel draws in ambient air and compresses it before delivering it to the intake manifold.
The amount of pressure the turbocharger adds to the intake air is called boost pressure. This is often measured in PSI (pounds per square inch) or BAR. The relationship between the compressed air pressure and ambient air pressure is called the Pressure Ratio:
PR = Pintake / Pambient
Supporting Parts
A turbocharger system requires additional components to function properly and safely:
- Wastegate: Controls boost pressure by diverting exhaust gas away from the turbine wheel when a predetermined pressure is reached.
- Blow-off Valve: Prevents compressor surge by releasing pressurized air when the throttle is suddenly closed.
Pros & Cons
Turbochargers offer significant advantages but also come with drawbacks:
| Pros | Cons |
|---|---|
| High efficiency (uses waste energy) | Turbo lag (delay in power delivery) |
| Massive power potential | Added complexity |
| Minimal parasitic loss | Intense heat management needs |
Superchargers: Instant Power
Superchargers take a different approach to forced induction. Instead of using exhaust gases, they are mechanically driven by the engine’s crankshaft via a belt, chain, or gear drive system.
Drive Mechanism
Because superchargers are directly connected to the engine, their speed is directly proportional to engine RPM. This creates a linear power delivery relationship – more RPM equals more boost. This direct drive system eliminates turbo lag, providing immediate throttle response.
Key Types
There are three main types of superchargers, each with distinct characteristics:
- Roots-type: Positive displacement superchargers that trap air in pockets between lobes and force it into the intake. Known for their distinctive whine and immediate low-end boost.
- Twin-screw: Also positive displacement but with a more sophisticated design featuring conical rotors that compress air as it moves through the unit, making them more efficient than Roots-type.
- Centrifugal: Functions more like a belt-driven turbo compressor with an impeller that accelerates air outward, then slows it in a diffuser to convert velocity to pressure.
Pros & Cons
Superchargers have their own set of advantages and disadvantages:
| Pros | Cons |
|---|---|
| Instant throttle response | Parasitic loss (steals engine power to operate) |
| Linear powerband | Generally lower peak efficiency than turbochargers |
| Simpler installation in many cases | Heat generation in the intake charge |
Conclusion & Application
Both turbochargers and superchargers have their place in performance applications. The choice between them depends on the intended use of the vehicle:
- Superchargers are ideal for applications where instant throttle response is valued, such as daily drivers or drag racing where immediate low-end torque is crucial.
- Turbochargers are better suited for applications where maximum peak power is desired, such as track racing or high-performance street applications where efficiency and ultimate power output are priorities.
Modern technology has also led to hybrid systems that combine both forms of forced induction to optimize performance across the entire RPM range. Understanding the fundamental differences between these systems allows enthusiasts to make informed decisions about which technology best suits their performance goals.