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Motor Age, July 2002 v121 i7 p21(5)
Displacement replacement: forced induction makes little engines act like big ones, but pay attention to the details. (forced induction enables car makers to increase engine power without increasing displacement)(Industry Overview) Jacques Gordon.
Full Text: COPYRIGHT 2002 Advanstar Communications, Inc.
THE QUEST FOR MORE POWER UNDER THE HOOD PROBABLY STARTED THE DAY AFTER THE first showdown between two horseless carriages. Those early one-lung engines needed a lot of help, and it seems that adding displacement was the most expedient remedy. Before the turn of the century some engines were displacing 10 liters and still only making 30 horsepower.
As carburetion, ignition and metals improved, power went up and engine displacement came down to sane levels. By the 1920s, the importance of cylinder filling was just beginning to be understood, but very little was known about how to achieve it. A few of the more adventuresome manufacturers began bolting charge stuffers to the end of the crankshaft. These early superchargers were relatively successful, but they had their drawbacks too, and as with all new automotive technology, they were used on only a small number of very expensive cars.
It wasn't until the fuel-starved '70s that automakers got serious about using blowers as a substitute for displacement on 'normal' cars, and it seems they have finally made it worthwhile. According to the Specialty Equipment Marketing Association (SEMA), almost 16 percent of the world's 2000 model year engines were built with forced induction, and that number is expected to increase to 42 percent by 2010. Many of these are industrial and big diesel engines, but according to the National Highway Transportation Safety Administration (NHTSA), the number of cars in the united States with forced induction has doubled since 1998 and is expected to double again by the 2005 model year. The u.s. aftermarket also is selling more turbochargers and superchargers for cars than ever before, and they're being used to make serious power for the street as well as for the track.
As the high-performance aftermarket grew during the muscle-car era, it was relatively rare for anyone to acid a supercharger to a street engine. Even though blowers were readily available, without extensive (and expensive) upgrades, the engine's inherent weaknesses quickly became obvious. Today's engines are much more highly developed, and while they are optimized for low emissions and fuel economy, most production forced-induction engines are almost the same as their naturally aspirated (N/A) brothers. There are still some important differences though, and also some failures and wear patterns unique to 'blown' engines. What can be gained from adding forced induction and how can the problems be avoided?
BREATHE DEEP...
An engine is an air pump. The more air that flows into the cylinder, the more fuel can be burned -- and fuel is power. Under ideal conditions, cylinder filling of more than 100 percent can be achieved in an N/A engine, but only in a highly tuned race engine. In a typical street engine, the throttle plate, turns in the intake manifold and the fact that the intake port is smaller than the cylinder bore all restrict the flow of air, so the cylinder will never be completely filled even when the piston reaches bottom dead center (BDG).
Flow restrictions can be at least partially overcome with valve timing and good manifold design. With a free-flowing exhaust system, exhaust gas will actually begin flowing out of the cylinder before the piston begins moving up on the exhaust stroke. Near the top of the stroke, the intake valve will begin to open and the exhaust out-flow will draw some intake air through the cylinder. Called 'scavenging,' this helps cool the combustion chamber and improves breathing because fresh air is already moving into the cylinder when the piston starts moving down the intake stroke. The piston stops momentarily at the bottom of the stroke, but the intake valve remains open a few more degrees to take advantage of the inertia that keeps the column of air moving through the intake manifold, thus ramming a little more air into the cylinder. Obviously the ram charging affect works best at wide-open-throttle (WOT) and over a narrow (and usually very high) rpm range, but ram charging can help race engines achieve up to 110 pe rcent cylinder filling. On a street engine, manifold design is at least partially determined by the space available under the hood, and valve timing and overlap are a compromise between power, emissions and driveability.
It's a lot easier and potentially less expensive to increase cylinder filling with forced induction. When air is forced into the cylinder at greater-than-atmospheric pressure, cylinder filling becomes less dependent on manifold design or engine rpm, and scavenging is greatly improved. This allows a wider choice of valve timing and duration, so the engine can be tuned to deliver power over a wider rpm range. As engine speed climbs, forced induction also slightly increases compression, which increases the amount of power released by burning the fuel.
THE NEW (PRESSURE) WAVE
Until recently, forced induction was primarily used as a way to increase horsepower, especially when boost was supplied with a turbocharger. Today instead of boosting horsepower, several manufacturers are using forced induction to make small engines deliver big bottom-end torque, the kind expected from a much larger engine.
By limiting the maximum manifold pressure but allowing that maximum to be reached at very low rpm, the fat part of the torque curve extends lower and stays fat longer. For example, the 2001 Saab 9-3 has a 2.0L engine, 9.2:1 compression and a small, fast-acting turbo limited to 7 psi boost. Peak torque of 184 ft.-lbs. is reached at only 1,900 rpm and remains the same all the way to 5,000 rpm. Volvo also is using a low-pressure turbo to enhance the torque curve of the 840 engine, which peaks at 177 ft.-lbs. at only 1,800 rpm. Volkswagen and Audi are using higher boost but still tuning it for low-rpm operation. On some of their engines, 90 percent of peak torque is available from 2,000 rpm all the way up to 5,000 rpm.
Aftermarket tuners are using the same technique, and it's a very effective way to increase power. According to Bob Keller, former Grumman aircraft systems engineer and now president of Turbonetics, many production-stock engines can realize a 30 to 40 percent power increase across most of the rev-range with only 5 to 7 psi boost. This represents a significant increase in total airflow through the engine, but most PCMs have enough range of control to handle it. With knock sensors, a healthy oxygen sensor and premium fuel, emissions will be almost unaffected. Higher boost levels usually require ECM modifications, an aftermarket ECM or even an additional Fuel Management Unit that simply adds more fuel according to boost level. These modifications are usually not street-legal, but higher boost not only reduces reliability, it often requires engine modifications that are more appropriate for competition engines. For most street engines, a low-boost turbo or supercharger is almost literally a bolt-on modification.
THE DOWN SIDE
Engines with low-pressure, low-rpm boost experience a little more mechanical stress than standard N/A engines, but less than a highly tuned N/A engine because high revs aren't needed to reach the fat part of the power band. Still, the engine should be well above idle when the boost comes on to avoid lubrication problems when oil pressure is at its minimum. It's normal for high-mileage engines to have low oil pressure at idle, but it can be a problem for engines with forced induction.
The 1990 to '92 VW Corrado has a scroll-type supercharger, and boost is controlled with the throttle opening. Boost is available by 1,500 rpm, and unneeded air is recirculated back to the intake side of the blower. By about 25,000 miles, the early engines experienced what VW called 'rod float' under light loads. It was eventually determined that with the boost available at such a low rpm, oil pressure was not high enough to prevent pounding the rod bearings. Seizure was rare, but clearances increased and the rods would rattle on the crank journal. VW changed the oil passages in the crankshaft and switched to 20W-50 oil, just to make sure oil pressure would be higher at a lower rpm.
Today the bottom end is strong enough in almost all engines to handle even mid-range boost with no problems, but other areas are more critical. To reduce emissions, the newest piston designs use the thinnest possible upper ring-land to minimize the space around the top of the piston where hydrocarbons can hide from the flame front. The rings themselves are low-tension to reduce internal friction, and they're thin and superlight to decrease the tendency to float or flutter at high rpm. These are all good arguments for low boost. Subjecting these pistons and rings to high boost will increase blow-by and possibly damage the upper ring-land, especially if detonation occurs.
MAINTENANCE IDEAS
As stated earlier, most production engines today are capable of handling low-pressure boost with virtually no modifications, but for all engines with factory or aftermarket forced induction, there are some maintenance items that require closer attention.
Absolutely the single most important thing is to prevent detonation, and that means using good-quality fuel. All manufacturers selling cars with forced induction recommend a minimum of 91-octane fuel. With the knock sensors and engine management programs used on production cars, the premium pump gas available inmost of North America and Europe is sufficient. Most aftermarket tuners/suppliers recommend the same thing for pressurized street engines.
Whenever manifold pressure is positive, the ignition system will be working harder to jump the spark plug gap. The kind of plugs used (platinum, iridium, etc) is not as important as their condition, along with the condition of the rest of the secondary ignition system. During normal maintenance, the plugs should be examined, and the cap, rotor, wires, resistors, connectors and coil or coil pack should be checked with an ohmmeter. You also could check everything at once with an oscilloscope.
Earlier-model turbo chargers often failed when the center bearings seized due to lubrication problems. When the engine was shut off, heat in the turbo housing caused the oil to coke. This not only reduced oil flow to the bearing, it also contaminated the bearing with a solid material that acted just like sand. Manufacturers recommended letting the engine idle for a minute before shut-down to circulate oil through the turbo and cool the housing. Today the center section of most turbochargers is water-cooled and quality units have ceramic bearings, so this problem is rare. Just to make sure, Keller recommends using 100 percent synthetic oil in all turbocharged engines, especially older ones without a water-cooled bearing housing. Synthetic oil is much more tolerant of high temperature, and when its temperature limit is exceeded, instead of turning to coke, the oil turns to a fine ash that dissolves in oil.
The most common lubrication problem now is with the oil supply lines, especially when an aftermarket blower has been installed. Usually the oil supply line for the turbo or supercharger is tapped into an engine oil galley that has relatively little flow. Sludge or other contaminants can collect in that galley, and when the galley is first tapped, they can he flushed into the blower.
When installing or replacing a blower, Keller recommends running the engine with the oil line disconnected from the blower just long enough to flush the galley. It might be tempting to install a filter in that line, but it should be removed after only a few hundred miles to prevent lubrication loss due to a clogged filter. Keller also noted that when a replacement turbo cartridge - the center section with wheels and bearings - fails and is returned for a warranty claim, some parts suppliers will only honor the claim if the original receipt shows that new oil lines were purchased along with the replacement cartridge.
When an aftermarket turbo or blower is installed, a larger air filter should be installed too. There is a tendency to use an air filter that fits the space available rather than one that meets the real needs of the engine. Bigger is better, and the filter should be changed more often on all 'blown' engines. Many engines also have an air bypass valve that should be checked for proper operation. The bypass valve eliminates what used to be the most common cause of turbo failure, repeated high thrust loads on the center bearings. If the throttle is closed while the turbo is spinning fast and making lots of boost, the pressure between the turbo outlet and throttle plate spikes - sometimes as high as 100 psi. This pressure places a huge side load on the turbo bearing and puts a brake on the impeller almost instantly. The bypass valve gives that pressure a place to go and reduces on-off-on turbo lag by reducing impeller braking. Depending on the car or system, the bypass air is either vented or routed hack to the i nlet side of the blower.
With gasoline engines lasting well over 100,000 miles, it's questionable whether a turbo or supercharger will live that long, but most fail due to lack of engine maintenance, driver abuse or foreign object damage (FOD). There are very few parts to wear out on a turbo or supercharger, and most can be rebuilt provided the rotating parts and housing haven't been damaged.
FUTURE MARKET GROWTH IS POSITIVE
In just the past decade, turbochargers and superchargers have finally matured into a reliable and viable way to increase power without increasing displacement. 'While there is a growing aftermarket for them, almost every manufacturer selling cars in the United States offers at least one engine with forced induction, and Ford and Toyota offer superchargers as a bolt-on option that can be purchased at the dealer.
Blowers will be used on more engines in the fixture because they make it possible for an engine to be small enough to deliver good gas mileage for around-town and highway driving, but still deliver lots of grunt when the pedal is down. The way blowers and engines are designed and built today has greatly improved reliability of the blower, maybe to the point where it will last the life of the engine. But their longevity will be determined mostly by how owners use their cars, and by how well you pay attention to the details while maintaining their engines. <hr></blockquote>
[ October 06, 2002: Message edited by: Dojo2000 ]</p>
<blockquote>quote:</font><hr>
Motor Age, July 2002 v121 i7 p21(5)
Displacement replacement: forced induction makes little engines act like big ones, but pay attention to the details. (forced induction enables car makers to increase engine power without increasing displacement)(Industry Overview) Jacques Gordon.
Full Text: COPYRIGHT 2002 Advanstar Communications, Inc.
THE QUEST FOR MORE POWER UNDER THE HOOD PROBABLY STARTED THE DAY AFTER THE first showdown between two horseless carriages. Those early one-lung engines needed a lot of help, and it seems that adding displacement was the most expedient remedy. Before the turn of the century some engines were displacing 10 liters and still only making 30 horsepower.
As carburetion, ignition and metals improved, power went up and engine displacement came down to sane levels. By the 1920s, the importance of cylinder filling was just beginning to be understood, but very little was known about how to achieve it. A few of the more adventuresome manufacturers began bolting charge stuffers to the end of the crankshaft. These early superchargers were relatively successful, but they had their drawbacks too, and as with all new automotive technology, they were used on only a small number of very expensive cars.
It wasn't until the fuel-starved '70s that automakers got serious about using blowers as a substitute for displacement on 'normal' cars, and it seems they have finally made it worthwhile. According to the Specialty Equipment Marketing Association (SEMA), almost 16 percent of the world's 2000 model year engines were built with forced induction, and that number is expected to increase to 42 percent by 2010. Many of these are industrial and big diesel engines, but according to the National Highway Transportation Safety Administration (NHTSA), the number of cars in the united States with forced induction has doubled since 1998 and is expected to double again by the 2005 model year. The u.s. aftermarket also is selling more turbochargers and superchargers for cars than ever before, and they're being used to make serious power for the street as well as for the track.
As the high-performance aftermarket grew during the muscle-car era, it was relatively rare for anyone to acid a supercharger to a street engine. Even though blowers were readily available, without extensive (and expensive) upgrades, the engine's inherent weaknesses quickly became obvious. Today's engines are much more highly developed, and while they are optimized for low emissions and fuel economy, most production forced-induction engines are almost the same as their naturally aspirated (N/A) brothers. There are still some important differences though, and also some failures and wear patterns unique to 'blown' engines. What can be gained from adding forced induction and how can the problems be avoided?
BREATHE DEEP...
An engine is an air pump. The more air that flows into the cylinder, the more fuel can be burned -- and fuel is power. Under ideal conditions, cylinder filling of more than 100 percent can be achieved in an N/A engine, but only in a highly tuned race engine. In a typical street engine, the throttle plate, turns in the intake manifold and the fact that the intake port is smaller than the cylinder bore all restrict the flow of air, so the cylinder will never be completely filled even when the piston reaches bottom dead center (BDG).
Flow restrictions can be at least partially overcome with valve timing and good manifold design. With a free-flowing exhaust system, exhaust gas will actually begin flowing out of the cylinder before the piston begins moving up on the exhaust stroke. Near the top of the stroke, the intake valve will begin to open and the exhaust out-flow will draw some intake air through the cylinder. Called 'scavenging,' this helps cool the combustion chamber and improves breathing because fresh air is already moving into the cylinder when the piston starts moving down the intake stroke. The piston stops momentarily at the bottom of the stroke, but the intake valve remains open a few more degrees to take advantage of the inertia that keeps the column of air moving through the intake manifold, thus ramming a little more air into the cylinder. Obviously the ram charging affect works best at wide-open-throttle (WOT) and over a narrow (and usually very high) rpm range, but ram charging can help race engines achieve up to 110 pe rcent cylinder filling. On a street engine, manifold design is at least partially determined by the space available under the hood, and valve timing and overlap are a compromise between power, emissions and driveability.
It's a lot easier and potentially less expensive to increase cylinder filling with forced induction. When air is forced into the cylinder at greater-than-atmospheric pressure, cylinder filling becomes less dependent on manifold design or engine rpm, and scavenging is greatly improved. This allows a wider choice of valve timing and duration, so the engine can be tuned to deliver power over a wider rpm range. As engine speed climbs, forced induction also slightly increases compression, which increases the amount of power released by burning the fuel.
THE NEW (PRESSURE) WAVE
Until recently, forced induction was primarily used as a way to increase horsepower, especially when boost was supplied with a turbocharger. Today instead of boosting horsepower, several manufacturers are using forced induction to make small engines deliver big bottom-end torque, the kind expected from a much larger engine.
By limiting the maximum manifold pressure but allowing that maximum to be reached at very low rpm, the fat part of the torque curve extends lower and stays fat longer. For example, the 2001 Saab 9-3 has a 2.0L engine, 9.2:1 compression and a small, fast-acting turbo limited to 7 psi boost. Peak torque of 184 ft.-lbs. is reached at only 1,900 rpm and remains the same all the way to 5,000 rpm. Volvo also is using a low-pressure turbo to enhance the torque curve of the 840 engine, which peaks at 177 ft.-lbs. at only 1,800 rpm. Volkswagen and Audi are using higher boost but still tuning it for low-rpm operation. On some of their engines, 90 percent of peak torque is available from 2,000 rpm all the way up to 5,000 rpm.
Aftermarket tuners are using the same technique, and it's a very effective way to increase power. According to Bob Keller, former Grumman aircraft systems engineer and now president of Turbonetics, many production-stock engines can realize a 30 to 40 percent power increase across most of the rev-range with only 5 to 7 psi boost. This represents a significant increase in total airflow through the engine, but most PCMs have enough range of control to handle it. With knock sensors, a healthy oxygen sensor and premium fuel, emissions will be almost unaffected. Higher boost levels usually require ECM modifications, an aftermarket ECM or even an additional Fuel Management Unit that simply adds more fuel according to boost level. These modifications are usually not street-legal, but higher boost not only reduces reliability, it often requires engine modifications that are more appropriate for competition engines. For most street engines, a low-boost turbo or supercharger is almost literally a bolt-on modification.
THE DOWN SIDE
Engines with low-pressure, low-rpm boost experience a little more mechanical stress than standard N/A engines, but less than a highly tuned N/A engine because high revs aren't needed to reach the fat part of the power band. Still, the engine should be well above idle when the boost comes on to avoid lubrication problems when oil pressure is at its minimum. It's normal for high-mileage engines to have low oil pressure at idle, but it can be a problem for engines with forced induction.
The 1990 to '92 VW Corrado has a scroll-type supercharger, and boost is controlled with the throttle opening. Boost is available by 1,500 rpm, and unneeded air is recirculated back to the intake side of the blower. By about 25,000 miles, the early engines experienced what VW called 'rod float' under light loads. It was eventually determined that with the boost available at such a low rpm, oil pressure was not high enough to prevent pounding the rod bearings. Seizure was rare, but clearances increased and the rods would rattle on the crank journal. VW changed the oil passages in the crankshaft and switched to 20W-50 oil, just to make sure oil pressure would be higher at a lower rpm.
Today the bottom end is strong enough in almost all engines to handle even mid-range boost with no problems, but other areas are more critical. To reduce emissions, the newest piston designs use the thinnest possible upper ring-land to minimize the space around the top of the piston where hydrocarbons can hide from the flame front. The rings themselves are low-tension to reduce internal friction, and they're thin and superlight to decrease the tendency to float or flutter at high rpm. These are all good arguments for low boost. Subjecting these pistons and rings to high boost will increase blow-by and possibly damage the upper ring-land, especially if detonation occurs.
MAINTENANCE IDEAS
As stated earlier, most production engines today are capable of handling low-pressure boost with virtually no modifications, but for all engines with factory or aftermarket forced induction, there are some maintenance items that require closer attention.
Absolutely the single most important thing is to prevent detonation, and that means using good-quality fuel. All manufacturers selling cars with forced induction recommend a minimum of 91-octane fuel. With the knock sensors and engine management programs used on production cars, the premium pump gas available inmost of North America and Europe is sufficient. Most aftermarket tuners/suppliers recommend the same thing for pressurized street engines.
Whenever manifold pressure is positive, the ignition system will be working harder to jump the spark plug gap. The kind of plugs used (platinum, iridium, etc) is not as important as their condition, along with the condition of the rest of the secondary ignition system. During normal maintenance, the plugs should be examined, and the cap, rotor, wires, resistors, connectors and coil or coil pack should be checked with an ohmmeter. You also could check everything at once with an oscilloscope.
Earlier-model turbo chargers often failed when the center bearings seized due to lubrication problems. When the engine was shut off, heat in the turbo housing caused the oil to coke. This not only reduced oil flow to the bearing, it also contaminated the bearing with a solid material that acted just like sand. Manufacturers recommended letting the engine idle for a minute before shut-down to circulate oil through the turbo and cool the housing. Today the center section of most turbochargers is water-cooled and quality units have ceramic bearings, so this problem is rare. Just to make sure, Keller recommends using 100 percent synthetic oil in all turbocharged engines, especially older ones without a water-cooled bearing housing. Synthetic oil is much more tolerant of high temperature, and when its temperature limit is exceeded, instead of turning to coke, the oil turns to a fine ash that dissolves in oil.
The most common lubrication problem now is with the oil supply lines, especially when an aftermarket blower has been installed. Usually the oil supply line for the turbo or supercharger is tapped into an engine oil galley that has relatively little flow. Sludge or other contaminants can collect in that galley, and when the galley is first tapped, they can he flushed into the blower.
When installing or replacing a blower, Keller recommends running the engine with the oil line disconnected from the blower just long enough to flush the galley. It might be tempting to install a filter in that line, but it should be removed after only a few hundred miles to prevent lubrication loss due to a clogged filter. Keller also noted that when a replacement turbo cartridge - the center section with wheels and bearings - fails and is returned for a warranty claim, some parts suppliers will only honor the claim if the original receipt shows that new oil lines were purchased along with the replacement cartridge.
When an aftermarket turbo or blower is installed, a larger air filter should be installed too. There is a tendency to use an air filter that fits the space available rather than one that meets the real needs of the engine. Bigger is better, and the filter should be changed more often on all 'blown' engines. Many engines also have an air bypass valve that should be checked for proper operation. The bypass valve eliminates what used to be the most common cause of turbo failure, repeated high thrust loads on the center bearings. If the throttle is closed while the turbo is spinning fast and making lots of boost, the pressure between the turbo outlet and throttle plate spikes - sometimes as high as 100 psi. This pressure places a huge side load on the turbo bearing and puts a brake on the impeller almost instantly. The bypass valve gives that pressure a place to go and reduces on-off-on turbo lag by reducing impeller braking. Depending on the car or system, the bypass air is either vented or routed hack to the i nlet side of the blower.
With gasoline engines lasting well over 100,000 miles, it's questionable whether a turbo or supercharger will live that long, but most fail due to lack of engine maintenance, driver abuse or foreign object damage (FOD). There are very few parts to wear out on a turbo or supercharger, and most can be rebuilt provided the rotating parts and housing haven't been damaged.
FUTURE MARKET GROWTH IS POSITIVE
In just the past decade, turbochargers and superchargers have finally matured into a reliable and viable way to increase power without increasing displacement. 'While there is a growing aftermarket for them, almost every manufacturer selling cars in the United States offers at least one engine with forced induction, and Ford and Toyota offer superchargers as a bolt-on option that can be purchased at the dealer.
Blowers will be used on more engines in the fixture because they make it possible for an engine to be small enough to deliver good gas mileage for around-town and highway driving, but still deliver lots of grunt when the pedal is down. The way blowers and engines are designed and built today has greatly improved reliability of the blower, maybe to the point where it will last the life of the engine. But their longevity will be determined mostly by how owners use their cars, and by how well you pay attention to the details while maintaining their engines. <hr></blockquote>
[ October 06, 2002: Message edited by: Dojo2000 ]</p>
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