The Turbo Goes Round And Round...

The dollar value of the word "turbo" has gone from zero to $17,200 in exactly 23 years. Back in 1955 Chevrolet introduced an eight-cylinder engine under the name Turbo-Fire V-8. The turbo prefix was a no-charge item, and the customers got what they paid for: nothing. Back then, the prefix was about as useful and descriptive as the letter h in oh.

But times are different now. We have a 55-mph speed limit and federal fuel-consumption laws and cars that are being designed as much for efficiency as glamour. Now, at the insistence of the engineers who design the cars rather than the people who name them, the word turbo is making a comeback that may just save the day for automobile enthusiasts. This time turbo refers to the real thing—a compact, turbine-driven supercharger—and as was not the case in 1955, you now must pay dearly in some cases for the prefix. Attaching it to a Porsche, as in Turbo Porsche, puts the price at $36,700, up a nice, round $17,200 over the less exotic 911 SC model. Part of that surcharge, however, goes for different brakes, wider wheels, special tires and modified bodywork necessitated by the dramatic increase in performance available with the Porsche turbo. Affixing a turbo to a Saab is more reasonable, a mere $9,998 instead of $8,098 for the non-turbo equivalent. If your taste runs to Detroit. Buick will serve up a Turbo V-6 Regal Sport Coupe as cheaply as $5,852.90.

These are the turbos you can buy today. More are on the way. Within months, Ford Motor Company will introduce a turbocharged four-cylinder engine for its 1979 Mustang and Capri. Chrysler Corporation has prototypes for four-, six-and eight-cylinder engines. And if the auto industry isn't moving fast enough for you, almost every decent-sized city in the U.S. has at least one shop that will custom-install a turbocharger on any car that rolls in the door.

The appeal of a turbo is that in effect it makes a big engine out of a small one. With proper design, the addition of a turbo provides a whopping power increase. The Turbo Porsche is a prime example. It has a six-cylinder engine of less displacement than any American V-8, yet it is the fastest production-line car currently being sold in this country. With no sterner urging than a firm foot on the gas pedal, it will accelerate from zero to 60 mph in 4.9 seconds and continue its double-time march right up to 165 mph. As thrill rides go, there are none finer, and for many enthusiasts that alone justifies the sticker price. But an even more remarkable aspect of the Turbo Porsche is the way it combines a thoroughbred's capacity for speed with the docile manners of a draft horse. You can idle it through clotted metropolitan traffic in top gear with the air conditioner on full blast and it will never hiccup. But point it toward the horizon and it will haul you there at three times the national speed limit. Considering the nature of today's federal laws concerning emissions and fuel economy, that sort of performance would be almost impossible to achieve without some form of supercharging, a catchall word for all devices that pressurize the air/fuel mixture being fed into an engine.

Turbochargers are the superchargers of choice these days because of their utter simplicity. An automotive turbo is about the size of a football and contains only one moving part, a shaft with a finned turbine wheel attached to each end. A streamlined housing surrounds each of the two turbines. All of the engine's exhaust gas is routed through one housing; all of the intake mixture of gasoline and air passes through the other. The flow of exhaust causes the turbine to spin for exactly the same reason that a pinwheel spins in a breeze. And this rotates the shaft, which, in turn, spins the intake turbine. Because of its design, the intake turbine acts as a high-efficiency fan that actually compresses the intake charge, allowing more of it to be ingested into the engine. More intake charge going in means more power coming out.

At first thought, the idea of using the energy of the exhaust to cram more charge down the intake has a kind of perpetual-motion-machine ring to it. But the engineer's equations say that it works. And so does practical experience. Turbochargers have become standard equipment on Indy cars. The legendary four-cylinder Offenhauser engine used at the Brickyard today displaces 161.703 cubic inches and would be very hard pressed indeed to make 400 horsepower on its own. But with a turbocharger adjusted for typical race conditions, the output rises to 750 horsepower. Indy drivers would be the first to know, and the first to blow the whistle, if pin-wheel power was the hoax it superficially appears to be.

The extent of the power increase available through turbocharging depends almost entirely upon how much the intake charge is boosted above atmospheric pressure. Boost is commonly referred to in inches—actually, inches of mercury, which is the same scale used by a TV weatherman when he says the barometric pressure is 29.92 and rising. Racers are not at all timid about the use of boost. In fact, Indy cars have more pressure in their intake manifolds than in their tires. For qualifying, the rules specify a limit of 80 inches, equivalent to about 40 pounds per square inch. But for the race, each team is left to its own discretion. Dan Gurney, the former Indy driver who now returns each year as a car owner, remembers 140 inches being used in one Offy. That is enough to turn out 1,100 horsepower. Of course, that much boost has been known to burst an engine like an overinflated party balloon. And even if the engine survives, there is the effect of the extra speed on the driver, who, according to Gurney, "can hold his breath only so long."

Actually, Indy drivers are relative newcomers to the thrill of turbochargers. The device was originally intended for airplanes, and that is probably its best application even today. Airplanes face a peculiar problem. The rarefied atmosphere found at high altitudes offers less air resistance, allowing aircraft to fly faster with no increase in power. But this same thin air also contains less oxygen, suffocating engines and severely decreasing power. In practice, a piston-engine airplane runs out of power before it reaches a high enough altitude to take advantage of the reduced air resistance. But with a turbocharger to compress the intake charge, sea-level horsepower is available at altitudes where man can no longer breathe without supplementary oxygen. The attendant speed improvement is well worth the complexity of an oxygen mask or pressurized cabin.

Still, somebody had to go up the first time and prove it. One of the earliest high-altitude pioneers was Captain Rudolph W. (Shorty) Schroeder of the U.S. Air Service, who set a world record of 28,900 feet in 1918. During the course of his testing of the then-new General Electric turbocharger, he set three more altitude records in 1919. All of this was accomplished in an open-cockpit plane. Schroeder was completely covered in sheepskin as protection against the cold. At these unprecedented altitudes, the hazards were unknown.

Finally, on Feb. 27, 1920, Schroeder reached 33,114 feet, yet another record. When he removed his goggles to change oxygen bottles, the—63� Fahrenheit air instantly froze his eyeballs. In the confusion that followed, the lack of oxygen caused Schroeder to pass out, and his plane dropped nearly six miles before he revived and regained control. Although he was almost blind, Schroeder found his original airport, McCook Field in Dayton, and landed safely.