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 and the first Chevy four-speed transmission, the ’57 Corvet
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 “doghouse” of the Ramjet system: the tall, thin intake manifol
03 This particular ’57 Corvette needed a quick swap-out of the fuel-injection unit in the
04 Take note of the spring inside the enrichment housing. Both its inherent strength, and
05 Here’s the high-pressure pump, disassembled. Inspect the pump shaft for wear, especiall
06 Pump-rebuild kits are available from multiple sources. Lockwood recommends the high-qua
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 the shaft, produced at the lip of the seal. Some shafts can la
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.
In addition, as doctors recommend to anyone whos middle-aged, exercising a fuelie on a regular basis is probably the best thing you can do for it. Since its a vented system, sitting still for extended periods of time can allow the fuel inside the fuel meter to evaporate and deposit a film of varnish. This buildup will eventually gum up the works. Also, it goes without saying that proper assembly and adjustment are essential. (The accompanying photos and captions illustrate what happens when these principles arent followed assiduously.)
08 As GM gained experience with FI, it was found that with the engine off, fuel could run
At this point, things can get complicated, as there were several variations on the FI theme, which well also highlight in the captions. As Rochester Products gained familiarity with the FI system, manufacturing methods were simplified (sand castings became die castings, for example).
Also, the subsystem that provides for cold-weather enrichment was improved, and the one that initiates fuel flow for engine starting was refined as well. Eventually attempts were made to increase the FI systems tolerance for hot weather. Even with all these changes, the fundamental operating principles remained unchanged for as long as mechanical fuel injection was in production.
In view of these changes, Lockwood points to the preferred original parts to use, along with some modern ones that can be integrated into the system to improve both its function and reliability, all without hurting the cars collectibility.
09 Lockwood feels that it’s very important to mount the anti-siphoning solenoid valve on a
10 The axle-and-link assembly is a key mechanism of the fuel metering. Over time, the pivo
Based on his years of experience, he notes out that there are two types of fuel-injection systems: those that have failed, and those that are going to fail. He attributes this eventuality to three aspects: wear, engineering flaws, and Bubbas (his term for general-purpose mechanics who arent familiar with the specifics of a Ramjet). Lockwoods basic advice: Look for damageand dont assume it doesnt matter.
Even when new, the Ramjet system was difficult to service, and few mechanics had the experience or tools to properly adjust it. (As a result, one unusual source for FI parts is from mechanics who replaced the system with a more familiar carb setup, and simply left the stock hardware on the shelf!) Despite this initial disdain by the uninitiated, the Rochester FI is now recognized as a classic design, seriously sought after by collectors of C1 Corvettes.
Thats in part because the Ramjet was a major improvement over the carburetors of the day. Unlike a carb, in which the venturi signal directly pulls fuel into the air stream, the venturi signal of the fuel injection tells the fuel meter how much fuel to pushor, more accurately, injectinto the air stream. Because this fuel-metering scheme was so much better than that of conventional carburetors, the problem of erratic mixture changes due to fuel slosh during hard cornering was completely eliminated.
11 The axle pin has to be free to rotate, with no resistance whatsoever. That means no Loc
12 The mushroom-shaped part on the right of this photo is called a “cranking signal valve”
13 Here’s a modern fix for a faulty cranking-signal valve: an electric fuel valve used in
14 Look for damage on the business end of the nozzles. If the bottom of the nozzle cup (no
15 As with other details of the FI units, the “spill valve,” which regulates the flow of f
16 This second design, generally referred to as the “good guy” spill valve, entered produc
17 The third and final design is known as the “thumbtack” spill valve, due to the shape of
18 The top of the nozzle should be checked for a split (seen here), a common problem that
Carburetors also suffered from a limited manifold size, due to the requirements of the operating range and the need for a hot spot during engine warm-up. The front cowl, carburetor, and air cleaner had to be low for clearance, and that height restriction interfered with achieving the ideal combination of driveability and high performance.
The Ramjet FI had none of these problems, but it had other issues. Being mechanical, it lacks the sensors that allow modern EFI systems to compensate for a wide range of operating conditions, such as changes in temperature and altitude. In spite of this drawback, it does a remarkably good job of adjusting fuel flow in response to changes in air density. Vintage racers looking for every advantage might find a reason to make minor adjustments on race day, but for normal street driving, the FI system can be calibrated once and then just left alone.
And when that Ramjet is working properly, the throttle response can make for a thrilling ride down memory lane.
|Fuel Injection Repair and Calibration