- Feb 6, 2007
Vintage Tech: The Granddaddy of EFI
More after the jump
The Chevy small-block made a big splash in '57 when it first came equipped with a Rochester injection system that allowed the 283 to growl out 1 horsepower per cubic inch. Prior to that, the Mercedes 300SL debuted an FI system in 1954. The Volkswagen Squareback's engine was as important as both of those mechanical systems, it not even more momentous in its own right. The "suitcase" iteration of VW's ubiquitous flat-four located under the rear cargo area was fitted with electronic fuel injection beginning in 1967. Metering hydrocarbons to the 1600cc air-cooled wonder was the first electronic fuel injection system suited for mass production, Bosch D-Jetronic. There was a system that preceded D-Jet. In fact, D-Jetronic traces its lineage directly back to the first short-lived and disastrous attempt at electronic fuel injection, ten years prior. The funny thing is, D-Jet was mainly the same system built with better parts; kind of like the IMSAI was an Altair that worked.
The D-Jetronic system was based on licensed patents and designs from Bendix. Bendix was a behemoth company that made everything from brake parts to avionics to radios and televisions, even computers. In the 1950s, Bendix had the talent and the expertise to devise a system that would be less mechanically complex through the magic of electronics. The Bendix system was initially for aircraft use, but the company put their propeller-heads to work on it and came up with a system that worked for the constantly varying throttle positions of an automobile.
EFI harnessed the newly affordable power of electronics. The Bendix engineers figured out that they needed to measure the pressure in the intake manifold and have the electronics perform some calculations against the constants (engine pumping losses, cylinder volume, fuel pressure), while also taking in to account a few other variables such as engine temperature and of course, throttle position. Sounds pretty much like a modern FI system, doesn't it? The microprocessor had yet to appear on the scene, and transistors were still expensive in the late '50s when the Bendix system came to market. It sounds novel to us now, but injector pulse duration and timing were controlled by a seperate set of points in the distributor. Ignitions would still be using points for many years, so an extra set for the FI was simply the only way to get the job done, and an elegant solution at that.
The Bendix system was fitted to a very small number of Chrysler products beginning in 1957. It was an expensive option that didn't last very long. The price was only half the reason for failure. The build quality of the system wasn't up to the task of being reliable in the automotive environment. While the basic design was sound, costs were cut where possible to bring the price down from astronomical to ridiculous. Even in the much cooler underhood environment of 1950s cars, the EFI systems failed at a fast clip. It did work, however, and Bosch saw the inherent promise.
In the decade between the Bendix "Electrojector" and Bosch debuting D-Jetronic, the cost of the electronic bits had dropped. Bosch also did a lot of work refining the design. It still used an manifold pressure sensor and triggered the injectors with their own set of points hidden in the base of the distributor. Bosch continued development on the system, adapting it to many different engines from Cosworth Vegas to Porsche 914s. Subsequent systems would be even better refined, using variable fuel pressure, controlling the pulse width and timing with microprocessors and integrating ignition functions and self-diagnostics. They generated many patents in the process and became quite adept at electronic engine management. So, while D-Jet is the granddaddy of EFI systems, it owes its existance to great-granddaddy Electrojector.
Excellent reference materials at Allpar and Rennlist were immensely helpful, as were many hours under the arse of a '69 Squareback.