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WHAT IS A TURBOCHARGER?

A 1915 patent submitted by Swiss engineer, Alfred Buchi, is often cited as the birth of the turbocharger. The design was for an exhaust-driven engine featuring a turbine and compressor mounted on the same shaft. The intention was to counter the loss of power experienced by aircraft engines at high altitude, but the prototype proved unreliable. Ten years later, however, Buchi successfully installed turbochargers on ten-cylinder diesel engines adopted by the German Ministry of Transport for passenger ships. Power was increased from 1,750hp to 2,500hp, leading to successful licensing of the design to a high number of manufacturers serving the marine, aircraft and railway industries. Turbochargers would be put to use in aircraft operated by the United States Air Force in World War II, though it wouldn’t be until the mid-1950s that the technology was seriously researched for automotive use.

The first turbocharged production car was the 1962 Oldsmobile Jetfire. A Garrett turbocharger with an internal wastegate was used. We’ll cover wastegates and their operation in a forthcoming issue of 911 & Porsche World, suffice to say the force-fed Jetfire’s power output was massively increased over the naturally aspirated version of the same model, but reliability proved problematic, and production ceased a year later. Experimentation with turbochargers in automotive applications (chiefly at the race circuit) continued, however, becoming widespread in the 1970s due to ever stricter emissions legislation and the 1973 global oil crisis, encouraging manufacturers, including Porsche, to look at how to extract big bhp from engines without having to significantly increase displacement. With homologation regulations for motorsport also playing their part, the dawn of the Turbo era had arrived, and although Chevrolet had already turbocharged an air-cooled flat-six with launch of the Monza Spyder a decade earlier, the 1975 911 Turbo (930) is the production car most associated with successful implementation of the technology.

Before we get too heavily into the workings of a turbocharger, let’s acquaint ourselves with what the part actually is. The basic principle is quite simple: think of a turbo as though it’s a big air pump. As exhaust gases exit the engine, they spin the turbine wheel of the turbo, which is connected to a compressor wheel at its opposite end. As the turbine wheel spins, so does the compressor wheel, and as the compressor wheel spins, it forces air into the engine at higher pressure than it would normally register, thereby creating what