Superchargers vs Turbochargers

Superchargers vs Turbochargers

Last Updated September 15, 2020 | Alison Smith

The power of an engine largely depends on how much air it can pull in. Both superchargers and turbochargers use forced induction to bring more air and more power to your engine. The main difference is that superchargers run off power from the engine, while turbos use exhaust gas created by the engine. Engines with a supercharger or turbo can produce much more torque compared to a naturally aspirated engine.

What Is a Supercharger?

Roush supercharger with white background

A supercharger is an air compressor that forces more air into an engine. They pressurize the air in the intake system to above atmospheric pressure. This makes the air entering the engine denser. On a supercharger, the impeller(s) are driven through the belt drive on the motor.

How Does a Supercharger Work?

Superchargers draw power mechanically from a belt or chain attached either to the engine’s crankshaft or an electric motor. They increase the air intake by compressing the air above atmospheric pressure without creating a vacuum. This pushes more air into the combustion chamber so more fuel can be added, which increases the overall power output.

Superchargers are usually powered by the crankshaft. Most use an accessory belt that wraps around a pulley. The pulley is connected to a drive gear that rotates a compressor gear. The compressor draws the air in and compresses it before sending it to the intake manifold. In order for the air to pressurize, superchargers have to spin fast. They can spin at speeds of 50,000 to 65,000 RPMs.

Because compressed air is hotter, the air must be cooled down before entering the intake manifold. If the air is too hot, it will lose its density and not expand as much during combustion. That’s why superchargers are often paired with an intercooler. The intercooler reduces the temperature so the density of the air increases.

Underhood shot of a supercharger on a New Edge Mustang

Types of Superchargers

There are a few different types of superchargers:

The main difference between these superchargers is how they send air to the intake manifold.

Roots Superchargers

Roots-type superchargers feature one of the oldest designs, dating back to the late 19th-century. Before they were used in automobiles, they were used to ventilate mine shafts. The Roots-type and twin-screw superchargers sit directly on top of the engine. They’re seen on most factory supercharged applications.

Roots superchargers have two rotors that are driven by a belt off the crankshaft. At the entrance of the supercharger, the rotors are spinning away from each other. The air enters and is sealed against the body of the housing inside the supercharger before passing through. Because the rotors mesh together, the air is unable to come back up through the intake.

With a Roots-type supercharger, more air is sent to the intake manifold. The pressure is built up within the intake manifold itself rather than the supercharger.

Twin-Screw Superchargers

With a twin-screw supercharger, you have two different types of rotors. The rotors mesh together, compressing the air along the rotor before exiting below. The air is compressed within the supercharger itself before it is passed along to the intake manifold.

Both Roots and twin-screw superchargers can be considered positive displacement superchargers. This means a fixed amount of air goes through with each revolution. The torque curve is wide, which will give you a boost across a large range of RPMs.

Centrifugal Superchargers

Where Roots-type and twin-screw superchargers sit on top of the engine, centrifugal superchargers sit closer to the front of the engine bay. They look similar to turbochargers but are driven by an engine belt instead of exhaust gases.

A crank belt rotates the impeller, which pulls in the air. The air comes in through the intake and travels through the compressor (and intercooler, if it has one) before being sent to the throttle body. It then passes through the intake manifold and on to the engine.

These types of superchargers aren’t positive displacements like the Roots and twin-screw styles. Centrifugal superchargers need to spin really fast in order to provide boost. At low RPM, the boost will be lower. The boost increases as the engine spools up.

Gearing can be used so the impeller rotates faster than the engine RPM. But peak boost will only be reached at peak RPM, so the torque curve is more toward the top end. Centrifugal superchargers tend to be smaller than Roots-type or twin-screw superchargers so it’s easier for them to incorporate an intercooler.

Electric Superchargers

Electric superchargers are similar to centrifugal but use an electric motor rather than a belt attached to the engine. A 48-volt battery usually powers the motor. How long it takes to spool up an electric supercharger will depend on how much energy is in the battery. The battery can recharge during coasting for better efficiency.

As long as there’s power in the battery, you can adjust the torque curve however you want. This means there’s little to no lag time. It can spool fully in as little as 0.5 seconds for instant max boost. Electric superchargers have a high rotation speed, reaching up to 120,000 RPM. That’s higher than some turbochargers. These systems are very powerful but can be complex, costly, and heavy.

What Is a Turbocharger?

Turbocharger with white background

Turbochargers are air compressors that use exhaust gas turbines to force more air into the cylinders. They’re more efficient compared to a supercharger, which needs power from the engine to run. Turbochargers can improve engine economy from 20-40%. Turbochargers are actually a form of supercharger, but they work differently.

How Does a Turbocharger Work?

Turbochargers use the velocity and heat of exhaust gases to spin a turbine that powers a compressor, or impeller, that forces more air into the engine.

There are two sides to a turbocharger: the turbine and the compressor side. Exhaust gases are used to spin the turbine at a high speed, upwards of 150,000 RPM. The turbine connects to a shaft that spins the impeller on the other side of the turbo to suck in cool air.

The impeller then compresses the air, forces it through an intercooler, and into the engine. A wastegate is used on the exhaust side of the turbo to regulate the gases. A blow-off valve is used to expel excess air after you take your foot off the gas pedal. That’s what makes the “whoosh” sound.

Turbo lag is the major downside with turbochargers. When your engine RPMs are high as you row through the gears, your turbo has no problem pushing compressed air into the engine. However, when you go to shift gears and your RPMs drop, there is a lag in exhaust gases coming from the engine. This results in a delay of compressed air coming off the turbo toward the motor. Because of this, turbos are best for mid-high ranges of the powerband.

Underhood shot of a turbo on a New Edge Mustang

Types of Turbochargers

Just like superchargers, there are several different types of turbochargers:

Single Turbos

Single turbos are the most traditional type of turbocharger. Single turbos come in many different styles. They can be large or small. Larger turbos have more top-end power, while smaller turbos spool faster for better low-end power. Single turbos are a cost-effective way to increase power or give a small engine more boost. However, they can have a narrow RPM range, so you’ll have to decide whether you want more low-end or top-end power.

Twin-Turbos

A twin-turbo is simply a two turbocharger setup. If you’ve got a V6 or V8, you can use a single turbo for each cylinder bank. You can also have one small and one large turbo. This can give you power in a wider RPM range. They’re more expensive as you’re essentially doubling a single turbo. Since there are more components, they can also be heavier.

Twin-Scroll Turbos

As an engine’s cylinders fire, exhaust gases enter the turbo in pulses. Twin-scroll turbos use two scrolls to separate the exhaust pulses. That means on a four-cylinder engine, two cylinders feed to one scroll while the other two feed to a different scroll. They have a divided inlet turbine housing and exhaust manifold that pairs the correct cylinders with each scroll. This prevents the pulses from overlapping and interfering with each other, which means less turbo lag. Twin-scroll turbos are more efficient and provide denser, purer air to the cylinders.

Variable Geometry Turbos

Variable geometry turbos (VGTs) are usually used in diesel engines with lower exhaust gas temperatures. They have a ring of aerodynamically shaped vanes in the turbine housing that rotate to vary the gas swirl angle. This means you’ll get less turbo lag and a wider boost range.

Variable Twin-Scroll Turbos

Variable twin-scroll turbos are a combination of a VGT and twin-scroll turbo. At low RPMs, one of the scrolls is closed to force the air to the other. At higher speeds, a valve opens to send air into the other scroll. It will give you the benefit of a twin-turbo setup but by using just a single turbo. Variable twin-scroll turbos allow for a flat and wide torque curve.

Electric Turbos

Electric turbos use an electric motor that spins the turbo’s compressor until the exhaust volume is high enough to do the work. This pretty much eliminates turbo lag and provides instant boost. They can be complicated and expensive, but you can get a wider RPM range with level torque throughout.

Differences Between Superchargers and Turbochargers

Both superchargers and turbos are forced induction systems that can add a lot of power. But each system comes with its own set of advantages and disadvantages.

Supercharger & Turbo Differences
Superchargers Turbos
Immediate power delivery Delayed boost due to turbo lag
Less efficient as they run off power from the engine More efficient as they run off exhaust gases
Can cause more engine strain Not as easy to maintain
Most cost-effective way to boost hp and torque Better fuel economy
Power gains across wider RPM bands Power gains across narrow RPM bands (unless using a twin-turbo)

Power

Either a supercharger or a turbo is going to give you more power. When you get that power, however, will vary. Turbos are going to have the smallest punch at low RPMs. This is due to turbo lag and because they spool slowly until the RPMs are high enough to spin the impeller.

Since a centrifugal supercharger is essentially a belt-driven turbo, it will see a similar curve and numbers throughout the powerband. Centrifugal superchargers and turbos make most of their power at the top end of the power band.

A twin-screw or Roots-type supercharger will give you a more linear torque curve. Because they’re belt-driven and sit right on top of the engine, all the compressed air goes immediately into the motor. This results in increased power outputs but a similarly-shaped power curve to that of a naturally aspirated engine.

So, a supercharger provides an instant boost, while a turbo has boost lag and has to spool up before delivering power. The downside of a turbo is that you don’t get that instant boost, but it’s more efficient than a supercharger. The supercharger has to use power from the engine, which will use more fuel.

Efficiency

Turbos are becoming a more popular option than superchargers due to their efficiency. Turbos are more common on economical cars looking for decent power but good gas mileage.

Automakers can use smaller four-cylinder engines with a turbo instead of a bigger V6. And turbo V6 engines have started replacing larger V8s in many performance cars and trucks.

Reliability

Superchargers provide good low-end torque and a linear curve throughout the powerband, which delivers reliable results. But superchargers can cause additional strain on the motor since they’re powered by the crankshaft. A turbo reuses exhaust gases that were going to exit the car anyways, so there’s no additional engine strain.

Superchargers are easier to maintain though as you don’t have to deal with wastegates or exhaust propulsion. They have their own contained oil system, while turbos share their oil supply with the engine.

Cost

Both superchargers and turbos can be quite expensive. Superchargers are usually more expensive than turbos but require less maintenance. Turbos are less expensive and more fuel-efficient but may cost more to maintain.

Sound

Superchargers are usually louder than turbochargers. Superchargers typically make a whining sound, whereas turbos have that “whoosh” sound.

Which Is Better, a Supercharger or Turbocharger?

Both superchargers and turbos can help your engine produce more power. There are several different types of superchargers and turbos, so finding the right one for you will depend on your needs.

If you want instant boost with no lag, a supercharger might be best. Superchargers can also get more power within a wider RPM band. Turbos are more efficient than superchargers, but they do have some lag time. They’re better for mid- or high-end power boosts.

But if you really want the best of both worlds, there’s always twincharging. Twincharging is when a car has both a turbocharger and a supercharger. Why pick one when you can have both?

Source: Car and Driver, Motor Trend, How Stuff Works, Engineering Explained

Superchargers vs Turbochargers

Superchargers and turbochargers are forced induction systems. They send more air to your engine for added power and boost. While superchargers are powered by a belt off the engine, turbos use exhaust gases. There are several different types of superchargers and turbos.