Explaining EFI

Even though replicas, by nature, steadfastly strive to step boldly forward into our automotive past, there’s no reason they can’t use a modern electronic fuel-injection (EFI) system. Kit car builders may want a nostalgic look, but they demand the driveability of a new car. This approach is now taking hold on all sorts of kit cars, and for good reasons.

The last carbureted cars rolled off the assembly line several years ago, and EFI is now the standard of the auto-manufacturing industry. Not only that, but EFI is catching on in the aftermarket, even for street rods, traditionally the bastion of old-tech hardware. When tuned-port injection first appeared on Camaros and Corvettes about 15 years ago, hot rodders could hardly wait to unbolt the tubular manifolds and yank out the nest of wires and sensors in order to install a more familiar carburetor and intake manifold. “No way I’m giving up my 650 Holley double-pumper!” they might have snorted a few short years ago.

Now, old-guard hot rodders—include kit car enthusiasts here, too—admit that EFI has a number of performance advantages. This is something that was already realized by the younger performance crowd, which has grown up without ever having to fiddle with carb screws to adjust the air/fuel mixture and idle speed. The reason for the change is simple: EFI simply works better. A computer-controlled engine is easier to start, is more driveable, and has less hesitation and stalling.

Added bonuses are increased fuel efficiency and reduced emissions. An EFI engine can also respond more quickly and precisely to the changing boost levels of turbos or superchargers. Road-course enthusiasts love EFI for its consistent fuel delivery, even on high-speed curves and uneven pavement.

For those not familiar with the technology, the system is not all that difficult to grasp. Yes, there’s a mysterious black box that is the brains of the outfit, but its job is fairly straightforward. This electronic control unit (ECU) does the same thing a carburetor is supposed to, only better—way better. It maintains an extremely precise air/fuel mixture, ideally at a 14.7:1 ratio, though that varies with engine conditions.

The ECU monitors input from a variety of sensors for the cylinder-head temperature, throttle position, fuel-injector pulse time, and engine revs. Other sensors might also include the manifold air pressure, oxygen, and air-inlet temperature. Based on that data, the ECU optimizes the air/fuel mixture hundreds of times per second by determining how long and when the injectors spray fuel into the port. Called the pulse width, the injector’s rate of fuel delivery is measured in milliseconds. Mentally compare that system with a carb’s mechanical choke-and-float bowl full of sloshing fuel, and you can begin to see why EFI is so much more effective. Of course, you have to pay a lot more for this level of performance. A typical carb-manifold setup for a Chevy V-8 runs less than $500, but figure on $2,500 to $4,000 for a complete EFI system.

Cold starts are a good example of how an EFI responds to changing conditions. When the ECU senses that the engine’s temperature is below a certain level, it enriches the air/fuel mixture to, say, between 11.0:1 and 12.5:1. Once the engine warms up and is at cruising speed, however, the ECU then leans it out to that sweet spot of 14.7:1. During heavy acceleration, the ECU may drop the level down to 12.5 again. If you’re driving in the mountains where the air is thin, the ECU can compensate for reduced atmospheric pressure. Getting a carburetor to handle all those changes is simply not possible without stopping to manually change the jets.

One key component of an EFI is the vehicle’s electrical system. Power demands are higher (high-amp fuel pump, processor, electric fan), so installing a 70-amp alternator on your project vehicle is a good idea. All of the connections, particularly the grounds on a fiberglass-bodied kit car, must be clean and secure. A poor electrical system can be the nemesis of EFI. Also, EFI requires a fuel-pressure regulator that automatically responds to changes in demand, and injectors need a fuel pump with much tighter tolerances and a fine filter to catch any impurities that might clog a nozzle. Injectors are available in a wide range of sizes so they can be tailored to the engine’s size, heads, and camshaft specs.

In addition, there are three types of injector firing systems: batch, bank-to-bank, and sequential. The batch type is the simplest, hitting all cylinders for every complete rotation of the crankshaft. However, this budget system usually requires more computer time to tune it properly. Bank-to-bank fires half of the cylinders for each half-rotation of the crankshaft. A sequential system pulses each cylinder on an individual basis. Most batch systems can’t accommodate changes in altitude, and the sequential system is usually for high-dollar racing or twin-turbo applications, so bank-to-bank is generally the best all-around way to go.

Aftermarket companies offer two basic types of ECUs: programmable and non-programmable. The advantage of a programmable type is that it allows the system to be set up for a specific application using either an internal flash program or a removable chip. The auto manufacturers’ computers have an advantage in terms of the millions of dollars of research behind them, but an aftermarket unit can be programmed more quickly with a laptop to make changes at the track or to adapt the engine to forced induction from a turbo, supercharger, or nitrous oxide. Another amazing aspect of EFI is that an engine can be tuned by phone line. Using a computer modem, a technician can tap into the ECU and check the readouts and fuel curves and make adjustments as needed in the programming of those fuel curves.

Rather than using bolt-in aftermarket units, some kit builders may be inclined to take a more do-it-yourself approach by combining and customizing an EFI system. That’s particularly true of the Cobra replica market, where the Ford 427 side-oiler is the engine of choice. Since that block is available only in limited quantities, there’s not much demand for engine builders to create a specific system for it.

Nevertheless, John Albus, a com-puter whiz by profession, found a way to install EFI on his Cobra replica, which was a custom project all the way through, with components derived from a number of sources and then modified. The brain of his beast is an Electro-motive TEC-II engine-management system that includes both an onboard computer and four coils replacing the distributor. The computer takes its crankshaft position readings from a magnetic pickup sensor mounted behind the harmonic damper. Auto-motion modified the Edelbrock Performer RPM manifold for a port fuel-injection layout, and Electromotive supplied a 1,600-cfm air door in place of a conventional carburetor.

In addition to singing the praises of the car’s driveability, Albus has actually tuned the engine via e-mail. A friend who was testing the car in an-other location several hundred miles away encountered some stumbling due to excessive richness in the air/fuel mixture when feathering throttle from a cruise condition. Albus, working on his home computer, adjusted the TEC-II program to lean out the engine from 2,000 to 4,800 rpm at cruise (but not full throttle) as a function of rpm versus manifold pressure. He then e-mailed this program to his friend, who downloaded it to a laptop and fed it to the engine’s TEC-II computer.

Correcting the problem took less than an hour of time. Try doing that by long distance with a screwdriver!