A car engine is essentially a large autonomous air pump; it sucks air in, compresses it, uses a small bit of fuel to initiate an explosive expansion of pressure, and exhales the "burnt" air/fuel mixture. The more air an engine is able to compress (and the more it is compressed) before it is ignited, the more powerful the ensuing explosion will be. That means more horsepower and a faster car!
But there are physical limitations to how much air an engine can take in. For one, ambient air at atmospheric pressure levels will only enter an engine at a certain rate. We can't very well increase the atmospheric air pressure of Earth-- that would be tough, and problematic for most forms of life! But what if there was a way to increase air pressure right before it enters the engine? Welcome to "forced induction"!
Natural Aspiration
This one is simple. When a car is "naturally aspirated", that means it doesn't have any sort of forced induction (no turbo, no supercharger). The engine draws air in at normal atmospheric pressure and creates its power without any help. While these engines are by far the most common, they're also less powerful than a counterpart engine that has some form of forced induction. That said, there is some peace of mind in knowing that there is no additional complexity to your engine; it can make repairs and maintenance significantly cheaper in some cases.
Turbocharging
Turbocharging is the most common way to gain a large increase in horsepower. Turbochargers operate on a pretty simple paradigm: It is a device placed in your exhaust system to "reuse" the super-heated and super-pressurized exhaust gases leaving your engine. At the exhaust passes through the turbocharger, it drives a turbine that forces air back into your engine's air intake.
There are a few benefits to using a turbocharger. Here are a few:
- They create a tremendous amount of power without adding much weight to your car.
- Because they're re-using energy in the form of outgoing exhaust gases, turbochargers have little to no effect on your fuel economy. In fact, they can actually sometimes be used to increase mileage!
But there are a few disadvantages as well:
- A turbo relies on exhaust pressure. When you step on the accelerator, there's a short time before the turbo is able to spool up and start forcing air into your engine (and thus start generating additional power). This is known as "turbo lag", and there are many factors in determining how severe it is.
- A turbo adds complexity to your engine. They need to be lubricated and cooled like any other part of your engine. They require additional maintenance to keep them working at optimal efficiency.
Supercharging
You'll find this type of forced induction on the fastest internal combustion vehicles on the planet: "Top Fuel" dragsters. Supercharging is similar to turbocharging, but differs in the method in which it powers its turbine. While a turbo uses outgoing exhaust pressure, a supercharger is directly attached to your engine's utility pulley assembly. This presents its own unique set of advantages and disadvantages.
First, the good:
- Because a supercharger is attached directly to your engine's pulley assembly, there is absolutely no "lag" between when you step on the pedal and when the supercharger starts generating additional power. The power is there, and the power is instant.
- They are subject to much cooler temperatures than a turbocharger, creating less "hot spot"-related issues in your engine compartment.
And the bad:
- A supercharger cannot generate peak power until your car is at redline (spinning the fastest). This is because it relies on engine speed and not exhaust flow to generate additional air pressure.
- It typically generates less power than a turbo, even at peak speeds.
- It still adds complexity to your engine, and requires periodic maintenance.
- Because it is directly attached to your engine, a supercharger takes a small toll on engine power. This may have a negative impact on fuel economy.
