Turbocharger & Supercharger Tech 101

OBJECTIVE: To educate our customers about the difference between a Turbocharger and a Supercharger including a clear definition of what a turbocharger & supercharger is, explanation how they add power to your vehicle, and technical information of their operation.

Altered Atmosphere Motorsports, Inc. is privileged to have worked with and serviced both Turbochargers and Superchargers on vehicles for over eight years now. In this basic training session we are going to learn the inner workings of a turbocharger & supercharger, their operation, what applications they excel in, and how they benefit the performance of your vehicle including its safety, efficiency, and power output.

What do Turbochargers and Superchargers do?

One of the simplest ways to increase the horsepower of an engine is to increase the amount of air and fuel that it can burn. Both turbocharger and supercharger are forced induction systems and use compressors to increase the amount of air forced into the engine. Normal engines will experience more power because for each stroke of the piston, the engine will receive more air. By compressing more air into the cylinders more power is created from each explosion in the cylinder, increasing the volumetric efficiency of the engine which makes it more powerful. Turbochargers and Superchargers typical boost between 6 to 10 psi (pounds per square inch) on a stock engine. Normal atmosphere pressure is 14.7 at sea level, so you are getting about 35 to 55 percent more air into the engine. From this, you can expect around a 35 to 55 percent increase in horsepower.

What is a Turbocharger?

A turbocharger is an exhaust gas driven compressor used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen entering the engine. A key advantage of turbochargers is that they offer a considerable increase in engine power with only a slight increase in weight.

A turbocharger is bolted to the engines exhaust manifold. The exhaust from the cylinders spins the turbine (exhaust wheel), which in turn spins a compressor wheel forcing air into the cylinders. The turbine is connected to the compress by a shaft. The compressor pressurizes the air going into the cylinders.

Here is another description, worded slightly differently: The engines exhaust from the cylinders passes through the turbochargers turbine blades, causing the turbine (wheel) to spin. The more exhaust that goes through the blades, the faster they spin. On the opposite end of the shaft that the turbine is attached to, a compressor wheel pumps air into the cylinders. The compressor is a type of centrifugal pump in which it draws air in at the center of its blades and forces if outward as it spins. This forced air is “forced” into the intake of the engine.

A turbochargers output is regulated by a wastegate. A wastegate is a valve that diverts exhaust gases away from the turbine wheel in a turbocharger. Diversion of exhaust gases causes the turbine to lose speed, which in turn reduces the rotating speed of the compressor which reduces boost pressure in your engine. The primary function of the wastegate is to stabilize boost pressure in turbocharger systems. The wastegate is controlled pneumatically by a wastegate actuator. To raise the boost pressure in your engine, a boost controller can be used to modify the performance of the wastegate actuator.

What is a Supercharger?

A Supercharger is a device used to increase the “effective displacement” and volumetric efficiency of an engine, and is often referred to as a blower. A supercharger is powered mechanically by belt- or chain-drive from the engine’s crankshaft.

Bolted directly to the intake manifold (roots type) or on the side of the engine (centrifugal), the supercharger drive pulley is attached to the internal impeller (compressor wheel) by a shaft. The drive pulley is attached to the engines crank pulley via a belt. As you increase the rpm’s of the motor, the supercharger’s internal impeller (compressor wheel) spins faster. This allows the supercharger to compress air inside of its casting before it forces it into the engine. The speed at which the impeller spins, determines how much boost can be produced. Changing the drive pulley is a simple way to increase or decrease your boost.

Safety & Efficiency

A turbocharger & supercharge can increase you vehicles safety via increased power. This increased power may help a vehicle merge in traffic and move out of harms way.

Because the compressor increases the pressure of the air entering the engine, a greater mass of oxygen enters the combustion chamber in the same time interval (an increase in fuel is required to keep the mixture the same, this mixture of air and fuel is called the air to fuel ratio). This greatly improves the volumetric efficiency of the engine, and thereby creates more power. The additional fuel is provided by the proper tuning of the fuel injectors.

This increased the engines "effective displacement". By pushing the air into the cylinders, it is as if the engine had larger valves and cylinders, resulting in a "larger" engine than it really is. So you have a lighter, more efficient engine that has the similar performance of a larger, less efficient high displacement engine.

SO WHAT IS THE DIFFERENCE?

Pros & Cons

A turbocharger is more efficient because it is using the “wasted” energy in the exhaust stream for its power supply. This means more overall power from the same amount of boost. There are ultimately many more turbochargers available than superchargers, so the user has an incredible number of units and trims available in which they can easily match the turbo to the demands of their engine and specific performance goal and/or requirement.

Because a turbocharger causes some amount of backpressure in the exhaust, a larger – and thus more expensive – exhaust system is required for best performance. A turbocharger also needs time for the turbine to spool up before boost is made. This is called turbo lag. Turbo lag can be undesirable because, when the turbo is spooled, a power increase may come abruptly resulting in a loss of traction and lost drivability / control of the vehicle. A supercharger creates no exhaust back pressure.

Because a supercharger connects directly to the crank pulley there is no lag. The compressor is always at speed and able to provide instant “boost”. The side effect is two fold depending on which type of supercharger you have. A roots or screw type supercharger will provide more boost at low rpms than a centrifugal supercharger. The roost or screw type supercharger is less efficient (and ultimately why this style supercharger has become unpopular) at mid-high rpms because of its bulk and inability to be as effectively intercooled. The centrifugal supercharger makes boost dependant to rpm, so if you have a kit that produces 7psi at 6,000rpm – it will only product 2 or 3 psi at 2,500rpm. A properly sized turbo system starts creating boost around 2,000rpm and can achieve full boost (7psi+) by as low as 3,000 – 3,500rpm. This results in a sizable mid-range power advantage for a properly sized turbocharger when compared to a centrifugal supercharger.

And, because a turbocharger uses “wasted” energy in the exhaust system for its power supply, the engine does not have a sizable power loss to operate the turbocharger. Because a supercharger is belt driven, it is always connected to the engine and there is always a power “drain” on the engine to power the supercharger – even at idle. In a 3.5L V6 application, turbochargers have produced 10-20% more power than their supercharger counterpart. In sever cases, as much as 1/3 of the total crankshaft power of the engine is required to operate a supercharger at high rpm.

Superchargers run a set boost pressure, and to increase boost you have to physically change the supercharger pulley and belt. With the addition of a boost controller, the output of a turbocharger can be changed “on the fly” without having to change any components.

When it comes to installation, superchargers generally have fewer components and are easier to install. Turbochargers are more complex, require exhaust modifications, and, because they have the potential to create more power, generally have more elaborate components. Inherently, because turbochargers have the capacity to create more power, they have a greater potential to crate more problems including engine damage when not setup and tuned properly.

Turbochargers generally are easier to maintain because they do not need to be serviced, other than the regular and recommended 3,000 mile synthetic engine oil change. Superchargers often need yearly belt adjustment and/or replacement, and have the same oiling requirements as a turbocharger.

Application

This is a hard subject because both a turbocharger and a supercharger is a practical method of increasing your engines power. When installed and setup properly, both systems can be reliable and fun.

For our customers who want to keep their vehicle simple, do not have a need to win every Friday night at the track, and want to keep the cost of their upgrades to a minimum - Supercharging is a great option. For our customers who are more demanding, want to have the fastest ride around town, want to have a vast avenue of upgradeability down the road (if they desire even more power), and is able to invest in several supporting mods for maximum reliability - Turbocharger is ultimately the #1 power adder.

Conclusion

By compressing air into the engine, both Turbochargers & Superchargers increase the “effective displacement” and volumetric efficiency of an engine. This, in turn, creates more horsepower and torque.
With the addition of an intercooler and proper engine (fuel & timing) management both Turbocharging & Supercharging is a viable way to increase the performance and driving enjoyment of your vehicle.

For more information or to have a member of the AAM Team help you select the best forced induction application for you vehicle, e-mail sales@alteredatmosphere.com or give us a call 301.330.8835!