Forced Induction Explained: Turbochargers vs Superchargers

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In car terminology, Forced Induction refers to the processing of compressing air and feeding it to the engine in order to get more power from it. As we all know, air is an integral part of combustion and its availability can make a world of difference in the energy released by it. Now, a normal engine can only take in a specific amount of air for combustion inside its cylinders, we call it a Naturally Aspirated engine.

But what if you need more power but can’t afford a bigger engine? Well, forced induction is your answer. It can be achieved by attaching a gas compressor to the Intake of the engine. It virtually increases the displacement of the engine while maintaining a smaller size. There are two common types of gas compressors used in internal combustion engines. They are Turbochargers and Superchargers.

Turbochargers

Image: Full-Race Motorsports

Aptly named, these make use of a turbine wheel driven by the velocity of exhaust gases coming out of the engine. The turbine, in turn, draws in more air, compresses it and then pushes it into the engine. More air results in a bigger boom, which translates to more power.

Sometimes, a turbocharger can get hot due to rising exhaust temperatures, which can heat up the air taken in by the engine. Hot air is low in density which, if you know your Physics, means fewer Oxygen molecules per unit volume of air. To combat that, an Intercooler is used in most turbocharging setups. It is a kind of a radiator made specifically for forced induction. It cools air by exchanging heat with the atmosphere. Colder air means, more Oxygen molecules per unit volume. That results in, you guessed it, more power.

Animation: Turbo Dynamics

Does that mean turbochargers are a solution to all our problems? Well, not quite. For you see, turbos, like all pieces of technology, have their flaws. The biggest one being Turbo Lag. Turbochargers, since they are powered by exhaust gases, require some time to build up pressure or Spool Up. This results in a delayed throttle response which kills the driving experience and can be frustrating for many. The lag can vary directly with the size of the turbo.

So if we use a smaller turbo, will the lag be reduced? Yes, however, a smaller turbo will not provide much power at higher RPMs. This is where Sequential Turbochargers come into play. The engine has two turbochargers; a small one and a bigger one. They are arranged in a sequence such that the exhaust outlet of the smaller turbo feeds into the exhaust inlet of the larger one.

So when you press the accelerator, the smaller turbo kicks in without lag, giving you instantaneous low-end grunt. As your revs climb higher, the larger turbo, which is already spooled up, kicks in, giving you the sweet top-end power.

Superchargers

Image: Super Chevy

Superchargers, unlike turbochargers, are directly driven by the engine via a belt, gear, shaft or chain. There are two types of superchargers: Positive Displacement and Dynamic. Positive displacement superchargers spin at the same speed as the engine, powering an opposite set of paddles or screws. They in turn suck, compress and then force the air into the engine. Their throttle response is instantaneous and they provide good low-end power with a linear power curve.

Dynamic superchargers have impellers that are also powered by the engine but spin at a faster gear ratio. When the air is sucked in, it is compressed via centrifugal force and the fed to the engine. Think of them as engine-driven turbos. And like turbochargers, dynamic turbochargers only work best at higher RPMs and suffer from lag as well.

Animation: Wikimedia

We’ll only talk about positive displacement superchargers here as they’re more common amongst manufacturers. They do, however, also come with cons of their own. The biggest one being efficiency. Superchargers are just not as efficient at delivering power than turbos. Some of the engine’s power is wasted in driving them. And since they’re at maximum boost all the time, they worsen the fuel efficiency of the engine even when not driven hard.

It’s more of a trade-off between what you prefer more and what you’re willing to give up. If you want instant power at the cost of fuel economy then go with superchargers. If you want more power at the cost of throttle response, then turbochargers are the best for you.

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