More than five-and-a-half decades have passed since the first mechanical fuel-injection system appeared on the C1 Corvette and full-size Chevy sedans, but its remarkable how well the system worked in its day. Developed by Zora Arkus-Duntov and John Dolza, the Rochester Ramjet FI still stands a breakthrough feat of engineering, long before the advent of computer-controlled induction in the early 80s.
With the 20/20 hindsight supplied by modern EFI LS engines, the Rochester unit might at first glance seem somewhat rudimentary. After all, it had just three basic components: a fuel meter, an air meter, and an intake manifold. Yet they kept a continuous supply of fuel accumulating behind the intake valves, ready and waiting for the valves to open, avoiding the fuel sloshing common to carburetors back then.
In contrast with the computer-controlled, sequential firing of individual injector nozzles used on LS engines, on the Ramjet, an air metering unit measures how much air is flowing into the intake manifold, then instructs the fuel-metering unit as to how much fuel should be sent to the engine. Mixing of the air and fuel begins within the nozzles themselves and continues in the cylinder head, in the path between the nozzles and the intake valves.
Theres a basic visual difference as well. The Ramjet is known for a tall, thin aluminum intake manifold nicknamed the doghouse. Keeping this unit in tune today, though, requires teaching an old dog a few new tricks.
We wont dwell on the engineering intricacies of the design, as that would literally take an entire book. (See The History of GMs Ramjet Fuel Injection on the Chevrolet V-8 and its Corvette Racing Pedigree, by Kenneth Kayser, for a comprehensive treatment of the topic.) Whats of more practical value to owners of these rare, vintage Ramjets is how to keep them running smoothly.
After all, this sort of expertise is not exactly common knowledge. Many carburetor-centric mechanics wont even touch a fuelie. Thats understandable, since in 1957, FI was a then-pricey $480 option, and out of all the 57 Corvettes made, only 16 percent (1,040 units) were fuel injected, according to the National Corvette Restorers Society (NCRS).
So dont expect to find a warehouse stocked with FI components. (Weve even heard of some Corvette collectors buying an entire car just the fuel-injection system.) As often as not, replacement parts have to be hand-fabricated by technically proficient experts, who can be hard to find.
Fortunately we came across one in the person of Jim Lockwood, an electrical engineer by training, and an avid Corvette collector by nature, who works on older fuel-injection systems as a hobby of sorts. He generously shared some of his in-depth knowledge with us, apparently out of goodhearted appreciation for the design of the unit, as he was quick to name fellow fuelie experts who can also be of assistance. (See the source list at the end of this article.) And he can barely handle the volume of work he has now.
In addition to providing tech and troubleshooting tips, well touch on how to repair and/or update specific areas that tend to suffer from wear and tear. Thats obviously an issue for anything thats more than 55 years old, and keeping this system in proper tune is essential for enjoying a classic Corvette.
While speaking with Lockwood, we also came away with a profound realization of just how sophisticated the Ramjet FI is as a milestone of mechanical engineering. As he put it, Its the most wonderful mechanical gadget, and does an amazingly good job of metering fuel in a broad range of conditions.
Even so, some basics on the care and feeding of this elusive system are in order. For instance, both the air and fuel meters are sensitive to contamination. A clean fuelie is a happy one.