Putting a five-cylinder gasoline engine into a car was a gamble for Audi, but the 100 was a big hit.
Engines with odd numbers of cylinders offer up a unique set of problems which for many years made them not worth the effort of developing. This wasn't as big a problem for diesels, but Audi's decision to build a five-cylinder gasoline engine for the 100 seemed as though it would be doomed to failure from the beginning. But not only did the engine work, the 100 would become a towering success for Audi, the car which made them into the brand they are today. The 100 was a car which took everybody by surprise right from the start.
Audi was a brand which had almost entirely died off after its parent company of Auto Union had been acquired by Mercedes-Benz in the Fifties. It was then bought by Volkswagen in 1964, and although the brand was revived under VW control, it wasn't exactly allowed to flourish. Sales of the original Volkswagen Beetle at this time were still so strong that VW simply could not build them fast enough. The acquisition of Auto Union from Mercedes-Benz was a move made essentially in order to get new manufacturing facilities in which to build the Beetle.
This included Audi's headquarters in Ingolstadt, and VW brass even put a freeze on any new model development from Auto Union brands, stretched as they were to build Beetles fast enough. But not everybody at VW was convinced that the Beetle would be such a massive hit forever, and this included an engineer named Ludwig Kraus, an employee who had been acquired along with Auto Union. Kraus knew that people, especially in North America, would eventually grow tired of the Beetle, and that it would be best if the company had something already in the works before the inevitable slowing down of sales.
So, even though the company had forbid the working on of new models, Kraus did so in secret. The first that VW's then boss, Heinrich Nordhoff, knew of the project was when he was presented with an early prototype. The car immediately changed Nordhoff's mind about new model development, and was given the green light. The car was first shown to the press in 1968 and was launched in 1970. Audi had by this point effectively absorbed the rest of Auto Union and adopted the four-ring design (which had previously denoted the four separate Auto Union brands) as its own. The timing of the 100's debut could not have been better.
The early Seventies saw the introduction of several new compact cars which almost immediately put consumers off of the Beetle. The more upscale but still small 100 was a gigantic success, much bigger than anyone at VW had expected, and as the Beetle's sales declined, more and more of VW's manufacturing space was taken over by the 100. This would start with the entire Ingolstadt plant and would eventually spread to part of VW's massive Wolfsburg plant. The car's four-cylinder engine ran a bit rough, but this really didn't seem to bother anybody, and what with Mercedes selling even more rough-running non-turbo diesel cars at the same time, the 100 seemed pretty easy to live with.
This would work to Audi's advantage, as the new five-cylinder engines would be introduced in 1977. The engine is inherently unbalanced, and early carbureted versions of the engine were also prone to uneven fueling of the cylinders. Fuel injection would come soon afterwards, but the timing of the five-cylinder engine's debut was as fortuitously timed as the debut of the 100 itself had been. The same year that the five-cylinder engine was introduced, the 100 became the first Audi model ever to sell 1 million units, and the car still had a long life ahead of it.
But the 100 was nearly killed off in 1986, with the very first case of unintended acceleration. Several reports had come out that the 100 would suddenly jump off the line for no reason when shifted out of park, and 60 Minutes ran a report which made the claim that this could happen at any time to any 100. The problem was, as the NHTSA would later conclude through its investigation, that there was nothing mechanically wrong with the 100. The problem was caused by buyers who were unaccustomed to how close together the pedals are in European cars, and as a result would step on the accelerator when they really wanted the brake.
So, since 60 Minutes was unable to reproduce a situation which never existed, they simply rigged up a 100 to rev out of control and reported it as though it was real. As you would expect, quite a few lawsuits would follow, but sales of the 100 fell to a fraction of their previous number almost overnight. But the 100 survived, and midway through the fourth generation in 1994 it was renamed A6, the name it still goes by today. Audi and VW still use five-cylinder engines, and actually have quite an amazing example of the breed in the TT RS. But it seems that Volvo is the company which now carries the five-cylinder banner to a greater extent. But it still all started here with the 100.