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DFI For The Masses

Taking a Closer Look at ACCEL's Gen VII

In previous issues, we've discussed some of the benefits of a quality aftermarket fuel injection system. As we've implied, simply converting from a carbureted system to an electronic fuel injection setup doesn't necessarily mean you're going to gain significant horsepower, but it does allow you to manipulate every parameter of the engine's functionality, which provides an infinite level of tuning for maximum performance. With a little fine-tuning, you can expect easier cold starts, increased fuel mileage, smooth idle, and exceptional part- and full-throttle quality from even the most radical combinations.

Converting to EFI may seem like a daunting task, especially if you're used to tuning a carburetor with a screwdriver. Although the concept is the same, which is to require similar air/fuel ratios for optimum power, all the mechanical hardware is replaced with computerized maps that match engine load and rpm with numbers. Fortunately, electronic fuel management systems like the ACCEL/DFI unit comes with a user-friendly CalMap calibration software to help you get started with minimal effort.

ACCEL's latest Gen-VII digital EFI system is available in several different configurations, from basic to extensive. The most basic systems include the engine control module (ECU); engine harness; MAP, TPS, IAT, ECT, and MST sensors; the CalMap software with an interface cable; and the instruction booklet. Accel also offers a bolt-in system for both big- and small-block conversions that includes its proprietary Pro-Ram manifold with machined billet aluminum fuelrails; stainless braided crossover tubes; an adjustable fuel regulator; CNC-machined, billet aluminum throttle-bodies (choice of 4150 or 4500 flange that flow from 750, 1,000, and 1,200 cfm); idle air control motor; high-output fuel pump; stainless fuel filter; all manifold fittings; throttle bracket; and high-performance fuel injectors.

There's also a complete Plug-n-Play system specifically calibrated for various crate-engine combinations, such as those offered from GM Performance Parts, and requires no tuning whatsoever. In fact, these systems come completely programmed from ACCEL, based on both engine dyno and real-world vehicle testing. That means you'll only have to find a place to mount the ECU, plug it in, and you're ready to go. About the most difficult procedure, if you can call it that, is to set the throttle-position sensor (TPS) for wide-open throttle. Simply turn the ignition key on (engine off), hit the corresponding key on the laptop, floor the throttle, and hit the key again to complete the procedure. And should you ever decide to upgrade the camshaft, heads, or manifold, you'll be happy to know that the system can be easily upgraded to take advantage of the added air.

Regardless of your setup, ACCEL/DFI can create a custom program for your specific application, making it even easier to get the engine fired up the first time. And if that isn't enough, the Gen VII includes a volumetric efficiency (VE) estimator that can create a basic VE table, eliminating any guesswork when determining a start-up fuel map. You'll need to fine-tune the VE table for peak power, and the map generated by the Gen VII will get you fairly close. Another invaluable tuning tool is ACCEL's wide-band oxygen sensor. While not everyone will need one, it's certainly an important tuning aid that'll accurately monitor air/fuel ratios when adjusting the fuel mixture.

While we've only scratched the surface on how powerful the ECU is with its various utilities and optional accessories, we'll prove it in the next couple of months. We're already tearing apart our 496ci big-block (see "The Fatter-Block!" Jan. '05) and plan on throwing a fairly stout huffer, namely a ProCharger F-2, on top of it with an air-to-air intercooler and shooting for some big numbers on pump gas. Combined with the Gen VII, we're going to show how a brutal mule can be toned down and made streetable with a few simple keystrokes. So whether you're looking for the easiest way to convert to EFI or need an EFI system that's capable of supporting copious power, have comfort in knowing that ACCEL/DFI can fulfill your needs. CHP


This little black box is the brains of the operation and can be used in several fuel injection modes, including sequential, bank to bank, batch, or staged batch. Since the ACCEL/DFI utilizes a Windows-based program, you'll need a laptop with Windows 98 or newer to interface with the software.

ACCEL offers several 4150-series flange throttle-bodies ranging from 750 to 1,550 cfm. All are CNC-machined to precise tolerances and feature hand-lapped throttle blades to provide minimum air leakage, stainless throttle shafts to resist corrosion, and come complete with the integral TPS and IAC mounts. The one shown here is a 4150 series that flows 1,350 cfm.

The Pro-Ram manifold is available in either oval or rectangular port configurations and is accepted by any conventional big-block cylinder head.

There are three versions of the CalMap software available. When the basic ECU is ordered with the wiring harness, you're limited to the screens you can access. The Sportsman Power Key plugs in between the laptop and the ECU, allowing you to manipulate most of the functions, while the Pro Power Key is strictly limited to ACCEL EMIC (engine management installation centers) and extraordinary combinations. If you order a basic kit and want to later upgrade, expect to pay $125 for the Sportsman and $150 for the Pro version.

It's critical to match the fuel injector flow to engine output. While the Plug-n-Play systems come with the correct fuel injectors for specific crate engines, other applications will not. To calculate the maximum fuel injector flow rate, follow this formula: (hp x brake-specific fuel consumption, or BSFC) / (number of injectors x .8). We highly recommend calling Accel directly for injector recommendations, especially with a supercharged or turbocharged application.

This one-bar (14.7:1) MAP sensor monitors the manifold vacuum and varies the output voltage to the ECU as a function of load placed onto the engine. Without it, the ECU wouldn't be able to control fuel enrichment.

ACCEL offers several high-pressure electric fuel pumps, including high-flow factory replacement pumps. When calculating how much fuel flow is needed, use ACCEL's formula: estimated hp x BSFC (use 0.5 for naturally aspirated, 0.55 for nitrous, or 0.6 for forced induction). The resulting number is the pound per hour required fuel flow.

It's always a good idea to upgrade the ignition system. ACCEL's Accupower 6 ignition features digital performance at analog prices and comes with the latest digital circuitry. The matching Accupower E-core coil produces a faster rise time and increased spark duration, making it superior to any factory unit.

ACCEL also offers 8.8mm spark plug wires with a resistance of only 150 ohms per foot and provides a 300 percent increase in electrical current delivery. We recommend investing in a set of soft fiberglass sleeves to protect the wires. For a few dollars more, it's a wise investment for any level of performance.

Every system includes the latest software along with a checklist of how the ECU has been calibrated.

The ACCEL/DFI is a universal piece of equipment, capable of adapting to any number of configurations. Should you ever want to adapt it to another engine combination, Accel offers a wide selection of fuel injector harnesses that simply plug into the main ECU harness.

Unlike conventional oxygen sensors, the five-wire, wide-band sensor produces different signals that allow you to read real-time air/fuel readings in a fairly steady state.

ACCEL's unique Dual Sync distributor produces a crank signal as well as a cam signal, with the cam signal being necessary for the sequential mode. All distributors have a billet housing and your choice of a large- or small-diameter cap.

The main screen features an instrument cluster that details all of the vital functions, both in real time and through the playback mode.

For new users, the volumetric efficiency estimator, or the main fueling table, provides a starting point by simply tapping in several engine parameters.

The Gen VII's data logger is able to replay data recordings in real time, point by point, and it can also be replayed in the volumetric efficiency table.

The VE table works in tandem with the air/fuel table. The purpose is to align the air/fuel ratio you're seeing to the target air/fuel you want. Increase the number to fatten up the mixture or decrease the number to lean it out.



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