T urbocharging and supercharging are both methods for forcing more air

into an engine. Forced induction increases the volumetric efficiency of an engine, allowing it to produce more horsepower. But forced induction can also be used to improve fuel economy. By turbocharging or supercharging a smaller displacement engine, a vehicle can get more miles per gallon without sacrificing performance. That’s the approach we’re seeing today with engines such as Ford’s EcoBoost V6 in the Lincoln MKS & MKT, Ford Flex and Ford Taurus SHO. The EcoBoost V6 delivers performance equivalent to a much larger V8, yet improves fuel economy 15%. Ford will have a 2.0L four-cylinder version of the EcoBoost engine in future Ford Explorer and Edge models.

It’s the same story with Audi and VW turbo diesel engines. Turbocharging is

used to boost the performance of a smaller displacement engine to deliver larger engine performance while maintaining high fuel economy.

A Brief HistorySupercharging and turbocharging are nothing new. The earliest supercharger applications date back to the late 1800s, and the first patent for a turbocharger was 1905. Early automotive applications were mostly limited to race cars built by Alfa Romeo, Bentley, Bugatti, Fiat and Mercedes.

During World War I, superchargers were added to many fighter plane

engines so they could climb higher where the air is much thinner.

This allowed British fighter

planes to shoot down German Zeppelins which were previously

immune to fighter attack at high altitude. During World War II, superchargers

and turbochargers were used on many

military aircraft to enhance both their

performance and altitude capabilities.

In the 1930s, superchargers were used on some luxury cars of that era

such as Duesenbergs and Cords to boost their performance.

In 1957, Ford offered a supercharged version of its Thunderbird sports car. In 1962, one of the first production applications for turbocharging was the air-cooled, rear engine Corvair Monza. A turbo was also offered on the Oldsmobile F85 Jetfire V8 engine that same year, boosting the 215 cubic inch engine’s power output to an amazing one horsepower per cubic inch (which was quite a feat in those days).

In the 1980s, turbocharging went main stream and was used on a variety of engines. Chrysler offered turbo versions of its popular 2.2 engines, Ford sold turbocharged SVT Mustangs and T-Birds, and GM created the legendary turbocharged 3.8L V6 Buick Grand National in 1982.

When the 1990s arrived, turbocharging and supercharging took back stage while fuel prices were relatively low. Americans

©2011 National Automotive Parts Association

Turbochargers & Superchargers

ISSUE 09.2011

Although turbocharging and supercharging have traditionally been used to boost power (as with this Buick Grand National), today the emphasis is on boosting fuel economy without sacrificing performance.

Ford’s new 2.0L EcoBoost engine will soon be available in Explorer and Edge models, and may eventually power up to 90% of Ford’s new cars and small SUVs. Turbocharging combined with direct fuel injection will help auto makers achieve higher fuel economy ratings.

} A Brief History

} What’s The Difference?

} Turbo Vs Supercharger

}  How Turbocharged And Supercharged Engines Differ

} Turbo Trouble

} Supercharger Trouble

} Service

}  Aftermarket Performance Upgrades

also started driving more SUVs with big V8 engines, so forced induction wasn’t seen as much of a necessity (except for the limited production 1992-93 GMC Syclones and Typhoons which featured turbocharged 4.3L V6 engines that made 280 horsepower and pushed these trucks from zero to 60 mph in just over 4 seconds!).

In the 2000s, a growing number of makes and models featured some type of optional forced induction system. Most of these were to boost performance, such as the supercharged Pontiac Grand Prix GTP, Mustang Shelby GT500, Ford F150 Lightning, Cadillac CTS, STS and XLR models, Corvette ZR1, and even some Chevy HHR and Cobalt cars. Compressor equipped Mercedes and turbocharged Audi and VW turbo diesels have also been built in significant numbers.

Today, the use of supercharging and turbocharging is growing rapidly, driven mainly by the need to boost fuel economy without sacrificing performance. In Europe, over 50% of all cars are turbo diesels. Less than 5% of U.S. cars are currently turbocharged or supercharged, but that number is predicted to grow to 25% or more within a few years as auto makers work to meet tough new Corporate Average Fuel Economy (CAFE) standards that will require a combined fleet average (cars and trucks) of 35 miles per gallon by model year 2020 or sooner. The current CAFE fleet average has been 27.5 mpg, but in model year 2011 the number rose to just over 29 mpg.

What’s The Difference?Supercharging and turbocharging accomplish essentially the same result but by slightly different means. A supercharger is a belt-driven compressor that forces air into the engine using rotors, screws or roller vanes. The most common type of supercharger for automotive production engines is the “Roots” style twin-rotor design with two counter-rotating two, three or four lobe rotors. This type of supercharger is called a “positive displacement” blower because it forces air into the engine under pressure at all engine speeds. This produces excellent throttle response and instant power.

Another type of supercharger is the centrifugal blower, which uses a belt-driven comperssor wheel, which is similar to that used in a turbocharger. With this design, air is pushed into the engine by the spinning compressor wheel. But the compressor does not develop much boost pressure until the engine is revved to about 2500 rpm or higher.

A turbocharger, by comparison, works like a centrifugal blower, except that it is driven by hot exhaust gases rather than a belt. As the exhaust exits the engine, the gases are routed from the exhaust manifold into the turbo turbine housing. The exhaust hits the blades on the turbine wheel, forcing it to spin at speeds up to 100,000

TECHtipsm When inspecting a turbo, remove the turbo air inlet duct plumbing and peer inside with a bright light. If the compressor wheel is damaged (broken, chipped or missing blades), the turbo needs to be replaced. The intercooler and rest of the inlet plumbing also needs to be inspected and cleaned to remove any debris that might enter the engine and cause damage.

m The turbo compressor wheel should spin freely. If it binds or turns roughly, the bearings are probably worn or damaged and the turbo needs to be rebuilt or replaced.

m The presence of oil on the compressor wheel indicates a leaky shaft seal on the compressor side. Oil on the exhaust turbine wheel (or blue smoke in the exhaust) would indicate a leaking shaft oil seal on the turbine side of the center housing.

m A scantool can be used to check the PID status of the waste gate on many applications, and to check the operation of the waste gate valve.

m Diagnostic trouble codes that indicate turbo troubles include P0033 (bypass valve control circuit), P0034 (bypass control valve circuit low) and P0035 (bypass control valve circuit high), P0234 (overboost condition), and P0235 to P0250 (various control faults).

A supercharger uses a pair of belt-driven rotors to force air into the engine under pressure. This improves the volumetric efficiency of the engine so it can produce more power.

The belt-driven compressor wheel inside a centrifugal supercharger builds boost pressure as its speed increases.

Oil varnish and coking on the shaft bearings is a common cause of turbo trouble. But wear or damage to either the turbine or compressor wheel can also prevent a turbo from doing its job.

Turbochargers & Superchargers

ISSUE 09.2011

RPM and higher. The turbine wheel is connected by a shaft to the compressor wheel on the other side of the turbo, which also spins at the same speed. This builds boost pressure and forces more air into the engine to make more power.

Boost pressure is limited by a device called a “waste gate” or “bypass control valve.” The waste gate works like a pop-off valve, and vents pressure to control both the rate of boost increase and maximum boost. On late model applications, the waste gate is computer controlled so boost pressure can develop more quickly to broaden the engine’s torque curve.

When air is compressed by a turbocharger (or a supercharger) it heats the air. Hot air is less dense than cooler air, and is more likely to cause detonation (spark knock). With most turbos, the air discharged from the turbine housing is routed through an “intercooler” (also called a “charge air cooler”) before it enters the engine. The intercooler can be an air-to-air or air-to-coolant heat exchanger. Air-to-air intercoolers are usually mounted ahead of the radiator and/or A/C condenser, and may have their own separate cooling fan.

Turbo Vs SuperchargerIn terms of efficiency, turbochargers are more efficient than superchargers (typically 80% versus 45%). The reason is because a supercharger requires mechanical energy from the engine to turn the rotors or compressor wheel while a turbo uses waste heat from the exhaust for a free ride. So at the same boost pressure, a turbo will usually make more power than a supercharger. Most production turbos and superchargers limit boost pressure to no more than about 11 pounds per square inch (PSI), and some superchargers limit boost to only about 5 PSI.

Five to 11 PSI may not sound like much, but compared to normal atmospheric pressure, it is quite an improvement. In a naturally aspirated gasoline engine, the intake manifold is under vacuum (negative pressure). When the throttle opens wide, there is only atmospheric pressure to push air into the engine (14.7 PSI at sea level). Boosting the pressure by means of a turbo or supercharger means the same engine can now ingest a much larger volume of air (which must also be offset with a higher volume of fuel delivery). The net result is that an engine under boost pressure breathes and performs like a much larger engine. But when extra boost isn’t needed, the engine uses no more fuel than before.

In supercharged or turbocharged race cars, incredible amounts of power can be realized by turning up the boost pressure to 20 PSI or higher. A 500 cubic inch drag motor can produce upwards of

2500 horsepower with a supercharger, and almost twice that with a pair of turbos! But this also requires expensive engine and drivetrain modifications to handle the extra power so things don’t break.

How Turbocharged And Supercharged Engines DifferVarious modifications are often made to turbocharged and supercharged production engines to make them compatible with forced induction, and to improve their reliability. Many of these engines have forged steel rather than cast iron crankshafts, forged or hypereutectic pistons, and steel or ductile iron piston rings rather than cast iron rings.

Other modifications include a slightly lower static compression ratio (necessary to prevent detonation under boost pressure), higher flow fuel injectors, special PCM calibrations, colder spark plugs, and usually less restrictive intake and exhaust systems. Many of these engines recommend using synthetic oil and/or more frequent oil and filter changes (every 3000 miles in many instances). The cooling systems on these engines must also be in good working condition to manage the extra heat.

Turbo TroubleCompared to superchargers, turbos can be more troublesome. The issue is heat. Because a turbo is exhaust driven, the compressor housing and interconnecting shaft tend to run very hot. The shaft bearings are cooled by oil flow, and the center housing usually has coolant routed through it to provide additional cooling. Even so, turbos undergo a period of heat soak when the engine is shut off after driving. This can cause the oil to burn and form coke deposits on the shaft bearings. Eventually, this can lead to bearing failure

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The construction of a turbocharger is fairly simple: an exhaust driven turbine wheel connected by a shaft to a compressor wheel. Under load, the unit can rotate at speeds of up to 100,000 RPM, which requires close manufacturing tolerances, heat resistant alloys and precision balancing.

In racing applications, such as this turbo drag car, extremely high boost pressures are used to produce incredible amounts of horsepower.

September ‘11 Tech’s Edge Questions: Turbochargers & Superchargers1. All of the following are TRUE about turbocharging and supercharging EXCEPT:a. Both can be used to boost

performanceb. Both can be used to improve fuel

economyc. Both are relatively new

technologies for today’s enginesd. Both increase the risk of

detonation (spark knock)

2. All of the following are TRUE about how boost pressure is created EXCEPT: a. The rotating rotors inside a

“Roots” style superchargerb. The spinning compressor wheel

in a turbochargerc. The spinning compressor wheel

in a centrifugal superchargerd. The spinning crankshaft inside

the engine

3. Any of the following may prevent a turbocharger from developing normal boost EXCEPT:a. A loose or slipping serpentine

beltb. Worn or damaged shaft bearingsc. Plumbing leaks between the

turbo and intercoolerd. Plumbing leaks between the

intercooler and engine

and turbo failure. Motorists are often advised to let a turbocharged engine idle for 60 seconds or so after driving at highway speeds to help cool down the turbo before they shut the engine off. Many turbos are designed so that coolant will continue to flow through the housing after shutdown to reduce temperatures. The classic symptoms of turbo trouble include:n Loss of power - Because the turbo isn’t

spinning as fast as it should and is not developing normal boost pressure. This can be caused by worn or damaged shaft bearings, airflow obstructions in the intake or exhaust systems, air leaks in the turbo discharge and intercooler plumbing, dirt or debris clogging the intercooler, or a leaky waste gate or defective waste gate electronic controls. Low boost pressure can also be caused by erosion wear on the compressor or

turbine wheels. The tolerances inside the housings are very close, so any increase in the clearances can reduce boost.

n Excessive oil consumption and/or blue smoke in the exhaust - Due to worn or leaky oil seals in the turbo bearing housing.

n Intake and exhaust manifold gasket leaks - Caused by boost pressure, corrosion and time. Intake plumbing leaks typically produce whistling noises when the engine is under load. Exhaust leaks will produce a familiar growl, hiss or rumble.

Supercharger TroubleNoise is a common complaint with superchargers. This can be caused by wear in the rotor drive gears or a low lubricant level in the supercharger gear housing. Most of the production superchargers on domestic cars are made by Eaton and incorporate a sealed oil supply in the housing for the drive gears. The oil level can be inspected by removing a plug, and adding the type of oil specified if the level is low. However, once the seals start to leak, the unit may be in danger of failing if the level gets too low.

Belt slippage can be another problem. The supercharger is driven by the same serpentine belt that drives all of the engine’s other accessories (alternator, power steering pump, water pump and A/C compressor). Belt tension is maintained by a spring-loaded automatic tensioner, which may become weak or corroded over time. Belts can also become worn or contaminated with oil, causing them to slip. This may prevent the supercharger from turning at its normal speed and developing normal boost pressure.

ServiceWorn or damaged superchargers and turbochargers are rebuildable, but it requires special expertise and equipment. OE parts are available in the ‘Speed and Performance’ catalog, check with your NAPA Auto Parts store, but it is not something a do-it-yourselfer or repair shop can normally do. The old unit is removed from the vehicle and sent to a specialist who does the rebuilding. Or, if the unit is unrebuildable, it must be replaced with a new or remanufactured unit. NAPA carries manufactured Turbo chargers in both the Cardone and Echlin lines and a line of manufactured superchargers from Cardone.

Aftermarket Performance UpgradesAftermarket supercharger and turbocharger kits are available for a wide variety of vehicle applications. Most of these tend to be for performance cars (Mustangs, Camaros, Corvettes, Challengers, street rods, hot rods, drag cars, and also many sport compact cars). Almost any engine can be equipped with a forced induction system, but it is not a simple bolt-on installation even with the best-engineered kits. It also requires reprogramming the engine computer, and may require additional engine modifications depending on the power level desired.

Performance shops that specialize in this type of work are the most qualified to make these kinds of modifications.

Answers: 1. c, 2. d, 3. a

The waste gate controls how fast a turbo develops boost pressure as well as peak boost pressure. A problem with this device may prevent the turbo from developing normal boost pressure, or worse yet, it may allow the turbo to over-boost the engine (which may result in severe engine damage).