Engine Basics: Turbos and Superchargers

One major component that makes a big difference when considering an engine is whether or not it has some form of forced induction. That's a fancy term for "blowing more air in." I think the best way to think about it is to imagine those old-fashioned bellows that folks used in fireplaces.



When you pushed air into the fire with the bellows, the fire was able to burn more, and it flared up. If you replace the bellows with a fan (technically a turbine, which is really just a fan with a ton of thin blades), then you get the idea. Induction simply refers to how much air gets to the fire. So forced induction can be thought of as "force-fed air into the motor."

There are two types of forced induction: turbochargers and superchargers. Both of these cause an engine to make more power by mechanically (basically, using a fan) to force more air into the engine than it can suck normally. The car also adds more fuel, and the result is more combustion. Combustion, after all, is a controlled explosion of gas mixed with air. Combine more gas with more air and you get more power. By using some of the engine's energy, you can turn the basically make the fire work its own bellows. This creates more power than the engine could make initially. I know that sounds kind of like a perpetual motion machine, but there are some limits on it, and so it's not really "free energy." It's just more energy.

So remember that there are two types. The first is a "turbo," or more properly, a turbosupercharger. Turbo refers to turbine, the fans that power the system. Charge is another name for the air that the system forces into the engine. Hence, turbocharger. This system gets the power it uses to turn the turbine (that forces more air into the motor) from the exhaust system. If you were to ever put your hand near your exhaust pipe while the car was running, you'd feel some pressure against your hand. This is normally "wasted energy" in a regular car. In a turbocharged car, one fan blade in the flow of the exhaust, which spins it like a windmill. The other side of the turbo has another turbine, which uses it's fan to compress ("boost") the fresh air and push it into the engine.


You can see the two halves of the turbo here. One side spins in the exhaust, one side spins to pull in fresh air. They are connected by a shaft.

Turbochargers are in many ways a very efficient way to tap into some extra energy. They tend to be more efficient that simply making a bigger motor to get the same power. But they only work when there is enough exhaust flow, so they don't make much power when at idle ("off-boost" or not working). That increases the fuel economy though. When you don't need the extra power, the turbo isn't working, and that means it's not sucking more gas along with all that air. The disadvantage is that it takes a second for the turbo to catch up with the exhaust flow. So if you floor the throttle, the exhaust starts shooting out immediately, but the turbocharger needs to get it's fan up to speed. That lag, which in modern cars is very small, is called (not very creatively) "turbo lag."

Superchargers are not really that different, but instead of dipping one side of the turbine into the exhaust flow, they simply get that rotational power from the motion of the engine itself. If you look at the front (sometimes, the side) of your car's engine, you'll see some belts that power certain accessories on your car. They spin, and they cause the accessories to function. A supercharger runs off of one of these belts, and uses it to do the same job as a turbocharger. As you can imagine, because the belt is always spinning while the car is on, the supercharger is always adding power, and it adds more proportionately to the speed of the engine. The disadvantage is that the engine is always making that power! So it always needs more gas. But there's no turbo lag, so you get that power whenever you want it.


You can see the supercharger on the front of the engine. On the left side is the pulley the belt attaches to.

I've tried to make it simple, but these are some pretty complicated systems. If you have a turbo or supercharger on your car and you want to learn more about it, or you're hopelessly lost, just write me an email and I'd be happy to answer your questions. Email contact AT sparkautoconsulting DOT com.