The fuel injection that rests on top of your Corvette's engine has gone through several stages of development. Each step of the way has been fueled (pun intended) by a continuing search for more power, fewer emissions, and better driveability. Fuel injection has progressed from the first mechanical fuel-injection (Ram Jet) units, which operated much like a carburetor, to the computer-controlled systems that seem to almost think for themselves. This transformation did not happen overnight, though. There have been several milestones in the procession toward perfect fuel injection.
Follow along and we'll take a look at the milestones that became stepping stones for the next generation.
The mechanical fuel-injection (Ram Jet) systems from Rochester were the first fuel-injection units for Corvette. They were designed to meter fuel according to the intake vacuum readings but, instead of allowing the fuel to be drawn into the intake according to the venturi principle, a regulated amount of fuel was introduced directly above the intake valve under considerable pressure. While still subservient to an engine's vacuum signal and capable of controlling only fuel, for the times, the system was a major improvement over carburetors. They controlled fuel better and were not subject to fuel sloshing in the float bowls during racing situations as was the carburetor.
GM engineers introduced the new Ram Jet fuel injection to the Detroit Section of the Society of Automotive Engineers, and touted it as capable of correcting carburetor deficiencies, improving fuel economy, and reducing hydrocarbon pollution. While it did help fuel delivery, several Achilles' heels hindered the system. Tuning it was one of the major problems. Being mechanical fuel injection, it did not self-adjust to accommodate changing situations. Changes in temperature and altitude could turn a great-running engine into an emissions-belching anchor.
Compared to today's computer-controlled systems, the mechanical fuel-injection systems are relegated to history and occasional drives to and from shows. They have a strong following, and Corvettes originally sporting these systems are highly sought after by collectors. There are subcultures within Corvettedom that deal exclusively with these early Rochester mechanical fuel-injection units. If the owner doesn't mind taking the necessary time to understand and care for these early FI units, driving a car with a Ram Jet can be exhilarating.
And driving them is probably the best thing you can do for them. They are a vented system, which means that if you allow them to sit for extended periods of time, the fuel inside the fuel meter will evaporate, leaving behind a film of varnish. Eventually, this buildup will start to affect the way the system operates, confirming the rumors about why so many of these systems were discarded in the first place. Whether you swear by the performance of these early Fuelie Corvettes or you swear at the mechanical fuel-injection systems, you'll have to agree this was the means by which GM broke the 1hp/ci barrier, and it took a fuel-injection unit to do it.