Forced Induction: Superchargers and Turbochargers

In the world of high-performance sports cars and race cars, super- and turbochargers are everywhere. Over time they've both become more common, with superchargers typically found on high-end muscle cars and turbos popping up on vehicles of all types, from supercars to economy cars. If you've ever wondered "What is a supercharger?" or "What is a turbocharger?" the quick answer is that they are the two most common parts used to achieve forced induction.

What is Forced Induction?

Forced induction forces more air into the engine allowing it to run more efficiently and make more power. Naturally aspirated engines (engines with no super- or turbochargers) make limited power due to air intake. Natural aspiration means that atmospheric force is responsible for pushing air into the engine. This force is about 14.7 lbs, and it varies with elevation. Turbo and superchargers have greater intake force for increased performance.

Naturally aspirated engines tend to only make a peak volumetric efficiency of 75% to 85%. While naturally aspirated engines can make more power through other upgrades to air intake and exhaust systems, they are unlikely to make 100% or higher efficiency without the help of forced induction. Forcing more air in gives each intake cycle more oxygen, which increases power by letting the engine burn more fuel and do more work. How much more power the engine makes, depends on how much boost the forced induction system supplies.

Boost refers to the amount of air that is forced into the engine and is measured in psi. The more boost, the more power the engine will make. That said, it’s important to make sure that the car’s engine and other components are built strong enough to stand up to the extra pressure. Otherwise that sweet super- or turbocharger might just blow up an engine from running it too fast. Other parts of the car may need to be modified to withstand the extra power too.

So, what is the difference between a supercharger and a turbocharger? Both use turbines to force air induction, but they turn the compressor a little differently. At their simplest:

  • Superchargers get their rotational energy from the serpentine belt or another drive belt
  • Turbochargers are powered by exhaust gases

Both use turbines to force additional air into the engine, speeding up the rate of air intake and allowing the engine to consume greater amounts of air. They differ in where they get the energy that is used to rotate the turbines.

How Does a Supercharger Work?

Superchargers are mechanically driven forced induction devices. In most cases, they are driven using a pulley that is wrapped in the serpentine belt. This allows the crankshaft to turn the compressor, creating boost for the engine so it can make more horsepower and torque.

They aren’t always driven by a belt. These are the different supercharger drive types:

  • Belt (V-belt, Synchronous belt, Flat belt)
  • Direct drive
  • Gear drive
  • Chain drive

Regardless of exactly how they are driven, superchargers get their power from the crankshaft. Depending on their configuration, they can consume up to 30% of the crankshaft’s energy! This makes them better suited for big engines than small ones.

For example: on a supercharged engine that generates 400 horsepower, the supercharger alone might consume 150 horsepower from the engine. This is a good trade-off, because it basically lets you trade 150 horsepower for 400, giving an increase in engine output by 250 horsepower. While it is a good trade, you need that 150 horsepower to spare if you’re going to install a supercharger.

How Does a Turbocharger Work?

Turbochargers are driven by exhaust gases. They feature two fans, a turbine and a compressor. Exhaust gas is routed through a tube in the turbo that turns the turbine, which sits in the exhaust stream. The compressor sits in the air intake, and because it is attached to the turbine, it spins with it. That’s how the compressor speeds up air intake to speed up the engine.

Because turbos get their energy from exhaust gases after they have exited the engine, they run more efficiently than superchargers, which rely on the crankshaft. This can help them make more power on smaller engines, and it also makes them more fuel efficient. That’s why turbochargers are increasingly common on economy cars and compact cars: they are one of the best ways to make more power from a small engine.

OE Turbos

Turbochargers have long been associated with tuned-up sports cars, but recently turbos have come as original equipment for all sorts of vehicles.

That’s because turbos are run by exhaust gases that must leave the engine regardless of forced induction, turbos increase the engine’s efficiency, and the fact that adding a turbo adds less weight than making the engine bigger does. As a result, turbocharged engines can weigh substantially less than similarly-powered naturally aspirated engines.

The other reason turbochargers are popular on economy cars is because of turbo lag. The turbo is driven by the engine’s exhaust gases, so it doesn’t kick in until enough is being exhausted. That creates turbo lag: the gap between when you first press the gas pedal and when the engine is at high enough an RPM to drive the compressor. That means that a turbocharged vehicle generates less power and uses less gas when driven at low RPM.

Be Smart About Forced Induction

Superchargers and turbos are commonly added onto cars by tuners in search of more power. Cars that come turbo- or supercharged stock are designed to operate with the power that is added by forced induction. A car that you decide to install forced induction onto may not be.

To further complicate things, these devices can provide different amounts of boost. An OE turbo will be designed by the manufacturer to provide a level of boost at which the engine can run reliably. Whether or not the same can be said for an aftermarket forced induction set-up depends on a whole host of factors, meaning you need to do a lot of research before adding forced induction to a vehicle.

Forced induction can help the engine make more power, there is such a thing as too much of a good thing. If you supply an engine with more boost than it can withstand, it can destroy the engine. Other parts may need to be upgraded to withstand the added boost too.

These are some common parts to be upgraded before adding forced induction:

  • Better Suspension: Upgrading struts, coil springs, anti-sway bars, and other suspension components can improve handling, which is crucial to keeping the car manageable when boosted
  • Cold Air Intakes: These give air a longer intake to travel, resulting in colder air entering the engine
  • High Flow Exhaust: Upgrades to the exhaust system can help alleviate back pressure by letting exhaust gases flow more freely
  • Performance Fuel Injectors: These are crucial to upgrade on vehicles that do not use a carburetor. While carburetors will adjust the rate at which they let fuel into the engine automatically, modern cars need new fuel injectors so that they can maintain the ideal air-fuel ratio with the new air from the boost
  • Intercoolers: Forced induction compresses air, heating up the air. Intercoolers cool off the air before it reaches the engine to keep it from running too hot

What all needs to be updated depends on the build, and how much boost you are trying to achieve. In order to withstand higher amounts of boost, more parts will need to be upgraded to withstand the added boost. There are also many parts that are used to install forced induction parts. Often you can get everything you need at once with a supercharger kit, which includes all parts necessary for working forced induction.

Regardless of the exact upgrades you choose to make, forced induction is a great way to increase the horsepower and torque output of a vehicle. It’s important to make sure the rest of your vehicle can take the boost, but there’s still no better way to make far more power than your vehicle is built for.

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