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.
01 Armed with Ramjet injection...
01 Armed with Ramjet injection and the first Chevy four-speed transmission, the ’57 Corvettes blew the Mercedes 300SLs and Jaguar XK-140s out of victory circles at road races across America. With a carbureted engine, a ’57 cornering in a tight apex would suffer from fuel sloshing and unpredictable air/fuel ratios. FI solved that problem.
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.
02 These two views show the...
02 These two views show the “doghouse” of the Ramjet system: the tall, thin intake manifold. The appearance of the doghouse changed somewhat over the years, but not the essentials of system’s operation.
03 This particular ’57 Corvette...
03 This particular ’57 Corvette needed a quick swap-out of the fuel-injection unit in the pits, in time for race day.
04 Take note of the spring...
04 Take note of the spring inside the enrichment housing. Both its inherent strength, and the adjustable tension on it, control when the FI unit switches between a lean, cruising mixture and a rich, power mixture. Three different springs were used between ’57 and ’65, reflecting increasing experience with FI and the introduction of more-modern cam designs. Install the wrong spring, or improperly adjust even the right spring, and you could end up with a lean stumble or an overly rich bog when accelerating.
05 Here’s the high-pressure...
05 Here’s the high-pressure pump, disassembled. Inspect the pump shaft for wear, especially near the squared-off end where the lip of a rubber seal typically wears a groove. If there’s any question about the condition of the shaft, replace it. Also inspect the end plate (right) for circular patterns created by gear rotation. Lap the end plate on 600-grit sandpaper on a surface plate to remove wear due to gears. Unfortunately, replacement parts vary in quality, so it’s important to take note of small details. For instance, a replacement shaft should have a shiny finish, and be of exactly the right size. Even a shaft undersized by 0.001-inch can cause free-play, and allow the tips of the gear to hit the cavity walls.
06 Pump-rebuild kits are available...
06 Pump-rebuild kits are available from multiple sources. Lockwood recommends the high-quality kits sold by John DeGregory.
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.
07 Note the wear grooves on...
07 Note the wear grooves on the shaft, produced at the lip of the seal. Some shafts can last decades, but not if subjected to debris. Dirt is the enemy of longevity.
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.