EFI for older carbureted engines is nothing new, though every year it seems as if interest in taking the EFI plunge just gains momentum. OEM vehicles have been fuel injected for so long that there are real car enthusiasts who have far more experience with EFI systems than with traditional carbs. Even us old-school gearheads have all experienced how well EFI can work, with late model performance cars and trucks showing flawless drivability and remarkable eliability. Still, for the vast majority of car guys, the thought of running a custom aftermarket EFI system remains clouded. Sure, it seems to work great on modern cars, but just what is involved in setting up an older engine to work with this modern technology? On the surface, it does seem pretty complicated, what with all the wiring, sensors, the control box, etc. Yeah, compared to four bolts and a fuel line, as with a carb, an EFI system is certainly more involved, but breaking it down, it's nothing a seasoned wrench-turner couldn't handle.

The first thing to realize is that the "high-tech" in a fuel injection is primarily already taken care of for you. Back in the early days, leading-edge EFI hackers were adapting the primitive OEM components of the time to vintage iron. These were the hard-core of EFI pioneers, the guys the who worked with soldering irons, voltmeters, custom-fabbed components, and cracked computer codes to marry old and new. Times have changed. These days, companies like FAST put out components designed to work together in a wide range of potential applications. Whether you are looking to inject an older big-block for a g-Machine project, or are looking to plant a modern, distributorless, coil-on-plug Hemi in your old Plymouth Duster, the systems to make it happen have already been ironed-out to the nth-degree.

The Hardware
Let's consider a retrofit of traditional iron first. We would normally see a basic intake manifold and carburetor bolted between the heads in a traditional four-barrel layout. Converting to EFI starts here, and fortunately this first hurdle isn't too tall. The intake manifold will need injectors installed--there are numerous machine shops around the country that can handle this task. Almost any intake can be modified with weld-in bungs for the injectors, though many later intake designs already have bosses cast in place and simply need to be machined for the injectors. The injectors simply slide in place, and are sealed with O-rings. To supply the fuel, injector fuel rails are normally used. For custom installations, universal rails are readily available from FAST or other sources. These need to be machined at the required spacing to accept the injectors, and have fittings installed at the ends for the fuel lines. If a custom installation is daunting, Edelbrock, Holley, and many others have injection manifolds ready to go for some applications, or you can send your manifold to FAST and have it converted with injectors and rails.

Obviously, once the manifold is converted you won't need a carb. Here an EFI system substitutes a throttle body, which is basically the same as the throttle valves on your carb. Aftermarket throttle bodies can be had in a broad range of configurations, but for simple conversions, universal throttle bodies with plain old Holley carb bolt patterns are readily available. The throttle body bolts on like a carb but it simply meters the air; it doesn't add any fuel. Like a carb, the throttle body hooks up via the throttle linkage to the accelerator pedal. While a carb has a screw to crack open the throttle plates and set the idle, with EFI the engine control unit adjusts the idle speed for you at whatever rpm you choose--and it adjusts the idle continuously for perfect idling under varying conditions. To do this job, the EFI throttle body does not jockey the throttle plates open and closed, but uses a little add-on device called the idle air controller (IAC). The IAC fits in a small passage that bypasses air past the throttle plates. It opens or closes this passage precisely depending upon how much air needs to get into the manifold to maintain a programmed idle, as directed by the control box. Most throttle bodies can be had with the IAC installed, or are designed to take common OEM units.

An EFI system depends on electronics to determine the fuel requirements, and it needs to know what's happening at the engine to get that job done. We find guys get a little intimidated at the thought of adding a host of mysterious sensors to an engine, but the pieces involved are very straightforward. The control unit needs to know how far the throttle is open, how hot the coolant and air are, the manifold vacuum, and it is really handy to know the air/fuel ratio at any given time. So we have the sensors for throttle position, coolant and air temperature, manifold air pressure (vacuum), and then the oxygen sensor for air/fuel mix. Nothing Earth-shattering about the sensors, most screw right into the engine as easy as installing a sensor for an aftermarket gauge. FAST sells sensor packs with everything you'll need to operate the engine with one of its systems.Of course, EFI uses much higher fuel pressure than a carb, and here you'll need to upgrade the fuel system. An EFI pump is needed that can provide 45-psi continuous pressure, and an EFI regulator is required to precisely set it. Pumps come in all sorts of capacities, and should be sized to meet the required horsepower demands. Again, a call to the FAST tech line will hook you up with a unit appropriate for the application. A provision for bypass fuel return from the regulator to the fuel tank is also required.

Turning our attention to the ignition system, the EFI control unit takes care of timing and advance functions normally handled by the distributor. Since the spark advance is dictated by the electronic control unit, the distributor must only function as a trigger and the timing set to a fixed reference point. To accomplish this, all the timing advance functions of the distributor must be locked out, including the mechanical and vacuum advance. A conventional distributor will allow for a bank-to-bank fired EFI system, but since the control unit has no reference to tell it what cylinder is firing, a sequential system cannot be operated in a timed sequence with the intake valve opening. To accomplish a timed sequential system, a second cam position reference signal needs to be sent to the ECU. This is just a reference that tells the ECU which cylinder in the sequence is firing. Dual-sync distributors have a provision for this signal, and are available from Mallory or MSD, while FAST is tooling up for a full line or these units.

The Brains
The heart of any EFI system is in the electronics and controls. Before the ready availability of aftermarket systems, it was very difficult to adapt a factory control unit to an engine and then adjust the parameters to deal with the particulars of the application. Modern aftermarket ECUs are designed to offer the user virtually unlimited flexibility in dialing-in the EFI system. We have had a chance to use the FAST XFI controller on a wide range of engine types, from traditional small- and big-block conversions, to some of the latest factory EFI offerings from Detroit--often with serious modifications. With the XFI, fuel and spark parameters are already programmed in with base settings, putting you in the ballpark as far as getting the engine fired and running. The simple setup menus let you fill in the blanks for the engine's combination and components. Various specifications like engine displacement, injector flow rating, number of cylinders, etc, are typed in, and then the operational parameters, like whether the injection system will be run bank-to-bank or sequentially.

Frankly, the XFI has a huge range of capabilities, and a really amazing range of flexibility in setting up the injection for an engine combination. To detail the full menu of what it does would fill a book, but here are some highlights. Besides the expected fully adjustable fuel and timing maps, there are fine-tuning maps for correction under virtually any condition or parameter imaginable. Temp correction, cranking and afterstart settings, closed loop settings, several idle functions, just to name a few. There are tables controlling fuel delivery with power adders, allowing for enrichment via the injectors when nitrous is operating, for example. There are boost controls, egr controls, torque converter controls, air conditioning clutch controls, individual cylinder timing and fuel controls, four auxiliary controls, a built-in sequential rev limiter ... you get the idea. The data logging capabilities offer a means of monitoring all of the engine, control, and sensor functions, as well as additional inputs from add-on sources, such as analog thermocouples to monitor temperatures.

The FAST system will quickly get you up and running, and the tuning procedure is very intuitive once one becomes familiar with the software. The operating software has extensive instructional and troubleshooting information built-in. FAST also has an entertaining video that gets into the nuances of the tuning process. If you'd rather not dig in at the "tuner-dude" level, there are a number of installation and tuning centers, as well as dyno shops, that can work on the tune.