Electronic Fuel Injection - EFI In A Carb's Clothing

Mooneyes' new EFI won the New Product of the Year(in its catagory) at the 2003 NSRA Street Rod Nationals

By Ron Ceridono

Building a traditional street rod brings together the curious combination of new and old. As a result, the challenge often becomes brewing a concoction that will produce modern performance using traditional-looking ingredients. Certainly when it comes to enhancing engine performance one of the best contemporary components available is electronic fuel injection, or EFI. EFI atomizes fuel more effectively than a carburetor, fuel distribution is generally improved, and by using a variety of sensors and a computer, air/fuel ratios can be more accurately controlled for a given engine requirement. The down side is, nothing looks more out of place in a vintage engine compartment than high-tech electronic gizmos and lots of wires.

On the other hand, few things look more at home in the engine compartment of a traditional hot rod than several Stromberg 97 carburetors. The down side here is that these mixers were introduced in 1936, which should make a number of facts obvious: (1) Lots of things have changed since then and many later carburetors are actually better (the 97's real strength was that the jets were easy to change), (2) Good 97 carburetors are becoming hard to find, and (3) When you do come up with some that can be resurrected, they're likely to be expensive. Truly, what the rodding world needs is a device that looks old, but is really new, something that has the form of a 97 but functions like a fuel injector. If you agree, read on.

Some time ago, when changing mechanical fuel injection to electronic operation first became popular, Ken Farrell of Classic Gass was one of the pioneers. If you don't recognize the name or the company it's because Ken is a hands-on guy and runs a low-key operation, spending most of his time in the shop, which is located in Long Island, New York. But while he and his company haven't been household names to most of the country, the Right Coast guys have been beating a path to his door for some time to have Hilborn, Enderle, Kinsler, Crower, and other mechanical systems converted to EFI. And while that will no doubt continue, it's a new product that is bound to find favor coast to coast.

Developed in conjunction with Mooneyes (who will also be the distributor), the two companies now offer EFI throttle bodies that look like Stromberg 97s. Now the best of both worlds have been rolled into one, call it high-tech nostalgia.Although these injectors share visual cues with 97s, they are all-new and unique castings--none of the parts, including the shafts and throttle plates, will interchange between the two. These new CNC-machined aluminum castings do feature a 2 5/8-inch air horn like the original, so standard air cleaners and scoops will fit and the throttle arms will accept standard linkage. In addition, both the old and new use the same mounting flange pattern and the fuel inlets are in similar locations. However, because the new injector doesn't require booster venturis, it will flow more air--225 cfm for the new compared to 175 for the old.

Like carburetors, fuel injectors come in many forms, but one way electronic fuel injection systems are categorized is by location of the injectors. Port systems, often called tuned port injection, or TPI, place the fuel nozzles just outside the engine's intake valves with one throttle assembly controlling airflow. An advantage to TPI is that fuel distribution is very well balanced. The other common fuel injection layout is called throttle-body fuel injection, or TBI. This style injection has the injectors above the throttle valves in one housing that looks much like a carburetor. So what is the Mooneyes EFI? A little of both. Like TBI, the Mooneyes system has the appearance of a carburetor, but the injectors are below the throttle valves. So, by using multiple TBI units, and spreading them out as multi-carb manifolds do, fuel distribution is more like TPI.

Of course the obvious question traditionalists will ask is, "How does Mooneyes injection system compare with multiple carburetors?" There's really not much comparison, the injection has the carbs covered. With multiple carburetors, a common three-two arrangement as an example, the carburetors open progressively. From idle to two-thirds throttle or so, the engine runs off the center carburetor. As the throttle is opened past that point, the end carburetors open, with all three reaching wide-open simultaneously. Obviously, fuel delivery to the cylinders will vary depending on throttle position. With the Mooneyes system, be it three, four, six, or eight injectors, all work in unison. As a result, fuel distribution is better balanced over the engine's entire operating range, from off idle to wide-open throttle.

Another means of classifying fuel injection systems is by the electronics that control them. They generally fall into one of two categories, mass airflow or speed density. The Mooneyes system is a speed/density-type, which means a variety of sensors are required: MAP (manifold absolute pressure), TPS (throttle position sensor), CTS (coolant temperature sensor), IATS (inlet air temperature sensor), and as an option, an O2 (oxygen sensor). Along with the sensors listed, an ECU (electronic control unit) is used. The brain of the system, the ECU gathers input from the sensors, then determines the proper amount of fuel for the injectors to deliver.

Although there are obvious advantages to being able to "tweak" the ECU of a fuel injection system, it's that very capability that scares some rodders away. One of the common complaints about "tune-able" fuel injection systems is that there are a bewildering array of changes possible, making it easy for a novice to get things out of whack. By comparison, the computer Mooneyes provides is sophisticated, but simple. Each Mooneyes system comes with the ECU custom-tailored to the engine it is destined for with operating parameters programmed in. However, if fine-tuning is required, a mixture trim control will allow a plus or minus 50 percent change in the injectors pulse width from programmed values. In simple terms, that means how long the injectors squirt fuel (and as a result, how rich the mixture will be over the entire rpm operating range) can easily be adjusted. As far as the injectors are concerned, they are sized according to the number used and the horsepower being produced. All other things being equal, an engine with three-twos (six injectors) will have larger injectors than an engine with six-twos (twelve injectors).

When it comes to traditional appeal, nothing has the visual impact of multiple carburetors; it's a given that a real hot rod should have the look of 97s. Of course, when it comes to drivability and reliability, visual appeal doesn't mean much and there's no comparison between modern electronic fuel injection and a bunch of leaky Strombergs. But now you don't have to choose, you can have carburetor form and fuel injection function, truly the best of both worlds.