Charge of the turbochargers

By , Special to The Christian Science Monitor

The ''turbocharger revolution'' still has a long way to go. Engine engineers, not only in the United States but in all the other automotive capitals of the world, are planning to fit these octopuslike ''blowers'' on additional future automobile engines, and the chances are good that up to one-third of all new cars will be turbocharged in the next few years.

Already, seven American and a dozen imported cars are available with turbochargers for more pep.

Indeed, this significant engineering trend has both advantages as well as minor disadvantages for car buyers of the world.

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This engineering trend has significant advantages and some minor disadvantages for car buyers.

Turbochargers are used primarily to provide more engine power, plus a bit more fuel economy, although this can be easily exaggerated. But they also add cost and frequently require more oil changes and more expensive fuel. Also, they can increase repair costs considerably because of the added complexity they bring to an engine.

Turbochargers are not new, of course. They've been around for more than half a century, especially in race cars.

So why, you ask, is the turbocharger bandwagon suddenly rolling into town?

There are several reasons, engine engineers say. The automakers have generally concluded that future automotive power plants must be fuel-efficient, lightweight, small gasoline or diesel engines, even for larger cars.

More recently a significant portion of the American public has concluded that it also wants better performance in its cars, something that has been noticeably lacking in many recent models.

The logical conclusion was: ''Let's go turbocharging.'' It will still permit the use of small, lightweight, and fuel-efficient engines, while providing the very desirable advantage of good acceleration and higher speed, when desired.

The name of the automotive ball game these days is flexibility. The turbocharger permits a manufacturer to use the same engine in either a ''hot'' car or an ordinary performer by simply installing or omitting the turbo.

Basically, a turbocharger is a fan or air pump that's driven by the velocity and expansiveness of the hot exhaust gas. It's also a little solace to the conservation-minded engine designers who have always been somewhat conscience-stricken by the large amount of engine heat that's continually being dumped into the atmosphere through the tailpipe of the car.

By spinning the blades of this air pump at speeds of 80,000 revolutions per minute or more, the turbo produces high-pressure air which, when injected into the engine with a charge of gasoline or diesel oil, produces significantly more power.

In other words, the turbo-equipped car performs - and that's what many car buyers want these days.

A major weakness of the turbocharger, however, always has been its ''lag,'' or inability to produce this extra power until the car is running at speeds of 25 to 30 miles an hour, simply because the exhaust flow isn't great enough at slower speeds.

Now, most of the auto companies are testing turbochargers with very balanced, smooth-running, and well-lubricated turbine wheels that can produce significant amounts of air-pressure boost at lower speeds, possibly as low as 10 to 15 miles an hour.

Because of this engine lag, Chevrolet as well as some other carmakers is leaning toward mechanical superchargers which are belt-driven by the engine crankshaft, providing the air-pressure boost at low speeds. But superchargers also take engine power and therefore are considered self-defeating by many engineers.

Turbochargers are also becoming increasingly popular in Europe and the Far East, because automobile taxes are generally based on the size of the engine. So the turbocharger permits the use of a very small, slightly taxed power plant, while at the same time providing good acceleration and mileage. The small engines result in lighter-weight cars, thus helping the fuel economy of the vehicle as well.

Besides the lag, another problem with turbochargers is that after some hot and hard running, the pressure builds up so much in the combustion chambers that the engine will start knocking.

To combat the problem, carmakers are using knock-limiters, which automatically retard the spark, thereby reducing both some of the knocking as well as the added performance. Too, the manufacturers are increasingly recommending premium unleaded fuel for these cars.

The knocking and potential other mechanical problems stemming from the high pressure and resultant heat are also controlled by the use of ''waste gates,'' which automatically dump the exhaust gases overboard after a certain critical point is reached.

All of this adds more cost and complexity to what is still probably a pretty worthwhile high-technology device.

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