Superchargers/Turbochargers

By Jeffrey Fazio
Special Sections Writer

SU|PER CHARG|ER n. an engine-driven compressor used in some motor vehicles to improve power by increasing the flow of air and fuel into the cylinders.

TUR|BO CHARG|ER n. a supercharger driven by an exhaust turbine. A turbosupercharger.

Think of a gasoline motor as being a fire in a fireplace. To get more heat (power) out of it, more fire is needed. There are two ways to do this: add more logs, which equates to adding cylinders to make a bigger engine; or blow air onto the fire to propagate flames, which equates to turbo- or supercharging an engine.

For example, the 2000 Chevrolet Camaro is available with a 3.8-liter V-6 engine that creates 200 horsepower compared to a 1998 Eagle Talon that creates 210 horsepower but from a turbocharged 2.0 liter engine.

A look at the racing community allows another comparison between horsepower created from turbocharged/supercharged engines and those engines that are normally aspirated. According to NASCAR rules listed on nascar.com, a stock car has a maximum 358 cubic-inch (5.866 liter) motor and produces around 750 horsepower. In contrast, a CART race car has a 2.65-liter turbocharged V-8 engine that produces over 900 horsepower, according to the CART rules listed on www.cart.com.

Although there are other differences between the design of these two race-car engines, the turbocharger is one of the largest contributors to the CART motor, making more power from half the volume of the NASCAR engine.

SAAB won the open class at this year’s Adephelia Pikes Peak Hill Climb with a turbocharged 2.0-liter SAAB 9-3 Viggen that was producing 750 horsepower. Like the NASCAR engines, the SAAB race car uses a block and head that comes straight from the manufacturer. The SAAB, however, produces 750 horsepower from 2.0 liters while the NASCAR car uses almost 6.0 liters to make its 750 horsepower.

The 2001 Buick Regal is offered with a 3.8-liter V6, with or without a supercharger. Without the supercharger the Regal is producing 200 horsepower. The supercharger adds 20 percent more horsepower to the Buick bringing it up to 240 horsepower. So how does a turbo- or supercharger make more power?

These components are basically air compressors, according to Garrett Co., a leading manufacturer of original equipment and aftermarket turbochargers. They force more air into an engine than would normally be brought in. Adding more air to the motor allows combustion to happen with greater power, increasing acceleration.

This pressurized air is measured in psi (pounds per square inch). The faster the compressor wheel of a turbocharger or supercharger is spun, the greater the boost (psi) created. The more boost pressure a car runs, the faster it will accelerate. The difference between a turbocharger and a supercharger is how they are powered.

A supercharger is spun by a belt that wraps around the crankshaft of the engine. A turbocharger is spun by exhaust gases passing through a wheel (much like a revolving door) in the exhaust side of the turbocharger. Superchargers are effective for creating a seamless power addition since they start pressurizing air as soon as the vehicle starts accelerating. The power is available on demand.

The downside of a supercharger is it can only ever be spun as fast as the motor since they are physically connected. The power created from a supercharger is smooth, but it is limited

Turbochargers, however, can produce almost infinite power. “Basically, the only limit you have is what you feel the strength of the engine will withstand,” explains Russ Angstadt, SAAB sales manager and master technician at Eisenhauer SAAB, Wernersville.

The limit on turbocharged power is the limit of a motor to withstand the pressure the turbo creates. Since turbochargers are spun by exhaust gases, the faster the motor goes, the faster the exhaust comes out which pushes the turbo faster which pushes the motor faster which pushes more exhaust, ad infinitum. It is an exponential process until the boost pressure is limited.

Boost is limited by a device called a wastegate. A wastegate vents boost pressure above a preset limit to prevent the turbocharger from producing dangerous levels of pressure inside of the motor. Another part used in conjunction with turbochargers and superchargers in modern vehicles is an intercooler.

Intercoolers work similarly to radiators, but instead of lowering coolant or water temperatures, they are used to lower the temperature of the turbo- or supercharged air. Lowering the charged-air temperature adds even more horsepower by making the air even more dense and also helps prevent detonation (or knock). Detonation is when the air and fuel mixture entering a cylinder is so hot that it explodes before the spark ignites it, causing the motor to knock. Knock negatively affects the efficiency and power of the motor.

Besides added power, there are other benefits to “charging” the air that enters a motor. Better gas mileage can be attained by turbo- and supercharged motors since the car can be driven without using the extra “boosted” power. Automobiles that create power from larger engines use those extra cylinders all the time, even at idle.

Again, looking at the 2000 Camaro, with the 3.8-liter engine, and the 1998 Talon, with a turbocharged 2.0-liter engine, the Camaro is estimated at 19 miles per gallon in the city and 30 mpg highway. The Talon claims 23 mpg city and 31 mpg highway. The big difference in gas mileage can be seen driving around town when the extra power is not generated.

Turbochargers also are environmentally friendly. The turbocharged SAABs already meet federal 2002 low-emission standards.Turbo- and superchargers allow an engine to be physically smaller and create the same horsepower.

There are numerous benefits of having a smaller engine. A smaller engine will weigh less than a larger engine. All things being equal, reducing the weight of a vehicle, following the laws of physics, will result in better gas mileage, greater acceleration and improved braking. A smaller motor with fewer cylinders also requires less oil and spark plugs and also has fewer internal engine parts.