Читать книгу Turbo: Real World High-Performance Turbocharger Systems - Jay K Miller - Страница 13

The postwar era saw little use of turbochargers at first, but gradually the turbocharger became a sought after component as postwar expansion gave rise to great economical development. Commercial manufacturers employing diesel engines, such as the Caterpillar Tractor Company realized that there was a constant increasing need for more power from their machinery. Without turbochargers, achieving power objectives would drive up engine size and cost. Certainly, a manufacturer who had twice the engine power versus a competitor would have a significant advantage.

The 1950s and ’60s saw a significant growth in turbo use. The primary growth took place in commercial diesel engines. This spawned the rapid growth of companies that would specialize in the development of turbocharging technology worldwide. The postwar economic expansion spawned rapid commercial growth, and more uses for turbochargers brought about expanded research and development from commercial competitors, which bring us to the modern era of turbo technology.

As turbo reliability and designs improved, the applications for turbos expanded. The muscle car era of the ’60s saw Detroit attempting to turbocharge a few gasoline automobiles such as the Chevy Corvair Monza and the Oldsmobile Jetfire. These applications were problematic at best. There are many opinions as to why turbochargers failed on this first attempt with production automobiles, but I maintain that the reasons are many.

The current Schwitzer-BorgWarner model S3 on the left has a slightly higher airflow range than the older Schwitzer model made in the ’60s for Cummins Engine Company. While the intended applications are different, it’s easy to see the dramatic design differences that have come about from computer-aided designs, improved materials, and manufacturing processes. (Courtesy Diesel Injection Service Company, Inc.)

The available engines were not designed to be turbocharged and there wasn’t a wealth of turbo application experience in the industry as it related to passenger cars. The turbo design that had to be considered for use on a carbureted engine had problems with durability and getting the fuel flow correct was problematic. Consumers could get all the horsepower they wanted with larger-displacement engines, high compression ratios, high-lift cams, and more. The Baby Boomer gear-heads weren’t ready for turbos. Besides, with gasoline at only 20 cents a gallon, who cared that you only got 6–8 mpg. Mileage concerns were for wimps! Wanna go fast? Cubic inches could get you there.

When the Arab oil embargo of the 1970s hit, spurred on by the clean-air act of 1977, Detroit began to focus on fuel efficiency and lower exhaust emissions. Smaller engines began showing up to burn less fuel and give consumers greater economy. But Americans still wanted their horsepower.

In the 1980s, Detroit returned to turbocharging as a way to achieve higher horsepower and performance for the now smaller engine packages. While some applications became famous such as the Buick Grand National, there were still problems in turbo land. The high exhaust temperatures seen in gasoline engines and poor maintenance by consumers weren’t the only challenges.

The technical problems associated with turbocharging by the average do-it-yourselfer mostly centered on the issue of whether to “pull through” or “blow through” the carburetor. If you used a blow-through method you would maintain optimum placement of the fuel distribution from the carburetor, through the manifold. But the problems associated with this method include boost enrichment of the fuel flow, because a carburetor senses airflow, not air density.

The pull-through method was favored by most application engineers because the turbo’s compressor was located downstream of the carburetor. This position in the system meant that the carburetor could sense the increase in volumetric airflow that was feeding the compressor prior to the turbo increasing the air density by building boost. In this way a separate boost-enrichement system for fuel to increase during boost conditions was not necessary, the carburetor mostly took care of it. The pull-through method, however, still had its problems because the air and gas mixture was run through the turbo’s compressor. This meant that the compressor cover must be tightly sealed with gasket sealer and/or an O-ring to the bearing housing so that raw gasoline could not leak out since it was now pressurized. The compressor would also act as a centrifuge to separate the gas from the air since the air and fuel dropets have different specific gravities. In addition, since the compressor was routed downstream of the carburetor’s throttle plate, the compressor was subjected to engine vacuum during light loads, or partial-throttle, no-boost conditions. Under such conditions, engine oil would be literally sucked right out of the turbo and into the engine. In order to solve that problem, positive type carbon face oil seals were used on compressors, but they were notorious for short life. Further, the drag on the turbine shaft caused by the positive type seals consumed a portion of the turbine’s power, thereby lowering the available energy to drive the compressor.

The rapid introduction of electronic fuel injection to gas engines in the ’80s was the great enabler. Electronic fuel injection meant no carburetor and no carburetor meant easier turbo retrofits! Aftermarket turbo systems could now be more easily installed. This led to a dramatic increase in interest in aftermarket turbo setups.