robin savell lloyd
Active Member
not mine but seems wise. Sports fans expect a competition of any sort to be settled with simple-to-grasp finality -- win or lose -- but things are rarely so straightforward when it comes to the technology of automobiles.
Take, for instance, the question of which is the best way to produce horsepower: A large, lightly stressed engine can deliver effortless acceleration, but it is likely to be heavy and thirsty; a small engine tuned for high output should be more efficient, though it may be finicky to drive.
Both approaches to producing power are widely used today, with mechanical refinements helping to minimize the drawbacks of each; neither method is a clear winner.
Likewise, there is no undisputed champion when it comes to deciding the best way to wring maximum power from an engine built for the latest high-performance model. Turbochargers and superchargers each have loyal followers ready to cite the benefits of their favorite power-booster.
Neither can claim to be new: The turbocharger recently turned 100 and the supercharger is even older. And despite their long histories, neither seems a clear winner.
Which is best suited to a vehicle depends on the intended use. With both alternatives at their disposal, engineers consider cost, driving characteristics and the space available under the hood to determine which system belongs where. Even on the same basic engine, the choice may change depending on the vehicle in which it will be used.
General Motors' four-cylinder Ecotec engine is a good example. It is supercharged when installed in the Chevrolet Cobalt SS and Saturn Ion Red Line, but turbocharged in the Saab 9-3 and the Pontiac Solstice GXP (a performance version of the roadster introduced this month at the Los Angeles auto show). In this case, the choice was driven by available space. Pontiac engineers might have been able to save some money by installing the supercharged version from the Cobalt, but there was room for only a turbo in the Solstice, whose engine is mounted front to back.
Turbochargers and superchargers are essentially pumps, raising output by forcing air into the engine rather than depending solely on the suction of the pistons to draw it in. (With more air, the engine can burn more fuel and generate more power.) Conversely, the same devices can be used to raise fuel economy by making smaller engines practical.
Alfred Buchi, a 26-year-old Swiss engineer, conceived the turbocharger in 1905 while researching gas turbines for a Belgian firm.
There's a hint of the perpetual motion fantasy in how his device works: The stream of hot exhaust gases leaving an engine spins a small turbine wheel that, in turn, drives a fan to pressure-feed air to the engine's intake side. Recovering some of the heat that would otherwise be wasted -- typically equal to one-third of the input energy -- improves efficiency.
The turbo's 100-year path to success was not smooth. The first challenge faced by engineers adapting them to aircraft engines was improving the life expectancy of a device that is super hot on one side, below ice cold (at altitude) on the other, and spinning at more than 30,000 rpm.
Vitallium was the breakthrough material for the hot spinning components inside turbochargers. Originally formulated for dentistry, this alloy was found to be strong at high temperatures, easy to cast in intricate shapes and generally superior to forged-steel turbine blades.
Countless improvements were needed to keep engines from blowing up under the high pressure developed by turbochargers. Because detonation is the Achilles' heel of any force-fed engine, high-octane gasoline developed for turbocharged engines in World War II fighters and bombers proved vital to making the technology practical.
Turbocharging took root in ships, trucks and locomotives; by the 1960s, it was ready for glamorous assignments in racecars and performance models. In 1962, the first turbocharged U.S. production car, the Oldsmobile F-85 Jetfire, took advantage of a water injection system developed by the military to avoid detonation.
The advent of emissions controls in the 1970s kept engineers busy perfecting anti-pollution devices like catalytic converters, exhaust-gas recirculators and fuel injectors. Porsche revived interest in turbocharging first by blowing away competitors in the Can Am racing series and then by giving its decade-old 911 a new lease on life by sticking a turbo in its tail. The Porsche 911 Turbo was the fastest car on the road when it arrived in 1975, prompting other automakers to introduce their own turbocharged models.
Initially, there was high anxiety over placing anything that would absorb heat between the engine's exhaust ports and its catalytic converter. The fear was that heat absorbed by the turbo housing would delay the catalyst from going to work. Engineers solved that problem by feeding extra fuel to the engine after a cold start, quickly heating the catalyst to operating temperature.
Turbo makers tried to reach beyond sports and performance models by proposing turbocharged four-cylinder engines as replacements for thirsty V-6s and V-8s. According to S. M. Shahed, vice president of Honeywell Turbo Technologies, "a down-sized turbocharged gasoline engine can deliver a 16 to 18 percent improvement when designed for fuel economy rather than sportiness."
Chrysler, for one, took that bait for a while and even built turbocharged minivans. But most makers concluded that their old-school engines were smoother and cheaper than the suggested replacements.
Automakers revived the supercharger -- a technology that predated the invention of the turbo by 20 years -- in the late 1980s as an alternative to the turbo. Driven by the engine's crankshaft instead of by its exhaust gas, the supercharger's main advantage was quicker response. Secondary benefits were simpler installation and lower cost. Naturally, turbo makers responded in kind. The next Porsche 911 Turbo is an advanced design aimed at building boost sooner and sustaining it longer; small computer-controlled vanes positioned inside the turbine housing twist to direct the exhaust flow for better low-speed response.
At the ultraluxury end of the market, where cost is not an issue, turbos are the booster of choice for Bentley, Maybach, and three Mercedes-Benz models. But as further evidence that neither approach can claim superiority, Cadillac, Jaguar, Land Rover and, yes, Mercedes-Benz offer 10 supercharged V-8 models. To further befuddle the wealthy, Mercedes sells its SL roadster and S-Class sedan with the choice of a supercharged V-8 or a twin-turbo V-12.
It gets better. Last fall, Volkswagen introduced a Golf GT in Europe that has both a supercharger and a turbocharger. The supercharger improves low-end throttle response; the turbo kicks in to help generate 168 horsepower from a tiny 1.4-liter engine.
Take, for instance, the question of which is the best way to produce horsepower: A large, lightly stressed engine can deliver effortless acceleration, but it is likely to be heavy and thirsty; a small engine tuned for high output should be more efficient, though it may be finicky to drive.
Both approaches to producing power are widely used today, with mechanical refinements helping to minimize the drawbacks of each; neither method is a clear winner.
Likewise, there is no undisputed champion when it comes to deciding the best way to wring maximum power from an engine built for the latest high-performance model. Turbochargers and superchargers each have loyal followers ready to cite the benefits of their favorite power-booster.
Neither can claim to be new: The turbocharger recently turned 100 and the supercharger is even older. And despite their long histories, neither seems a clear winner.
Which is best suited to a vehicle depends on the intended use. With both alternatives at their disposal, engineers consider cost, driving characteristics and the space available under the hood to determine which system belongs where. Even on the same basic engine, the choice may change depending on the vehicle in which it will be used.
General Motors' four-cylinder Ecotec engine is a good example. It is supercharged when installed in the Chevrolet Cobalt SS and Saturn Ion Red Line, but turbocharged in the Saab 9-3 and the Pontiac Solstice GXP (a performance version of the roadster introduced this month at the Los Angeles auto show). In this case, the choice was driven by available space. Pontiac engineers might have been able to save some money by installing the supercharged version from the Cobalt, but there was room for only a turbo in the Solstice, whose engine is mounted front to back.
Turbochargers and superchargers are essentially pumps, raising output by forcing air into the engine rather than depending solely on the suction of the pistons to draw it in. (With more air, the engine can burn more fuel and generate more power.) Conversely, the same devices can be used to raise fuel economy by making smaller engines practical.
Alfred Buchi, a 26-year-old Swiss engineer, conceived the turbocharger in 1905 while researching gas turbines for a Belgian firm.
There's a hint of the perpetual motion fantasy in how his device works: The stream of hot exhaust gases leaving an engine spins a small turbine wheel that, in turn, drives a fan to pressure-feed air to the engine's intake side. Recovering some of the heat that would otherwise be wasted -- typically equal to one-third of the input energy -- improves efficiency.
The turbo's 100-year path to success was not smooth. The first challenge faced by engineers adapting them to aircraft engines was improving the life expectancy of a device that is super hot on one side, below ice cold (at altitude) on the other, and spinning at more than 30,000 rpm.
Vitallium was the breakthrough material for the hot spinning components inside turbochargers. Originally formulated for dentistry, this alloy was found to be strong at high temperatures, easy to cast in intricate shapes and generally superior to forged-steel turbine blades.
Countless improvements were needed to keep engines from blowing up under the high pressure developed by turbochargers. Because detonation is the Achilles' heel of any force-fed engine, high-octane gasoline developed for turbocharged engines in World War II fighters and bombers proved vital to making the technology practical.
Turbocharging took root in ships, trucks and locomotives; by the 1960s, it was ready for glamorous assignments in racecars and performance models. In 1962, the first turbocharged U.S. production car, the Oldsmobile F-85 Jetfire, took advantage of a water injection system developed by the military to avoid detonation.
The advent of emissions controls in the 1970s kept engineers busy perfecting anti-pollution devices like catalytic converters, exhaust-gas recirculators and fuel injectors. Porsche revived interest in turbocharging first by blowing away competitors in the Can Am racing series and then by giving its decade-old 911 a new lease on life by sticking a turbo in its tail. The Porsche 911 Turbo was the fastest car on the road when it arrived in 1975, prompting other automakers to introduce their own turbocharged models.
Initially, there was high anxiety over placing anything that would absorb heat between the engine's exhaust ports and its catalytic converter. The fear was that heat absorbed by the turbo housing would delay the catalyst from going to work. Engineers solved that problem by feeding extra fuel to the engine after a cold start, quickly heating the catalyst to operating temperature.
Turbo makers tried to reach beyond sports and performance models by proposing turbocharged four-cylinder engines as replacements for thirsty V-6s and V-8s. According to S. M. Shahed, vice president of Honeywell Turbo Technologies, "a down-sized turbocharged gasoline engine can deliver a 16 to 18 percent improvement when designed for fuel economy rather than sportiness."
Chrysler, for one, took that bait for a while and even built turbocharged minivans. But most makers concluded that their old-school engines were smoother and cheaper than the suggested replacements.
Automakers revived the supercharger -- a technology that predated the invention of the turbo by 20 years -- in the late 1980s as an alternative to the turbo. Driven by the engine's crankshaft instead of by its exhaust gas, the supercharger's main advantage was quicker response. Secondary benefits were simpler installation and lower cost. Naturally, turbo makers responded in kind. The next Porsche 911 Turbo is an advanced design aimed at building boost sooner and sustaining it longer; small computer-controlled vanes positioned inside the turbine housing twist to direct the exhaust flow for better low-speed response.
At the ultraluxury end of the market, where cost is not an issue, turbos are the booster of choice for Bentley, Maybach, and three Mercedes-Benz models. But as further evidence that neither approach can claim superiority, Cadillac, Jaguar, Land Rover and, yes, Mercedes-Benz offer 10 supercharged V-8 models. To further befuddle the wealthy, Mercedes sells its SL roadster and S-Class sedan with the choice of a supercharged V-8 or a twin-turbo V-12.
It gets better. Last fall, Volkswagen introduced a Golf GT in Europe that has both a supercharger and a turbocharger. The supercharger improves low-end throttle response; the turbo kicks in to help generate 168 horsepower from a tiny 1.4-liter engine.
