Holley Avenger EFI System Install - The Conversion Factor

But the fact is that many aftermarket EFI systems have become much easier to install and tune. Easier still is Holley’s Avenger EFI system that doesn’t even require a new intake manifold and can literally have you swapped from a carburetor to EFI in a matter of hours. The Avenger EFI system is unique, as it replaces any carburetor with a computer-controlled throttle-body injection system. What’s more is that the TBI unit simply bolts onto your existing intake manifold so there’s no need for new gaskets, draining the coolant, and all the extra expenses.

Despite the fact that it’s a throttle-body injection system and not a multiport EFI, (Holley makes those too) the Avenger EFI is powerful enough to work with a variety of engine and horsepower applications from 275-600 hp and with cfm ratings from 600-900 cfm. So it can work on anything from a Chevy 250ci inline-six, a street-performance small-block 350 V-8, or a 502 big-block bracket-race motor.

Installation is simple and we looked on as Rob Green, of JKR Racing in Orange, California, installed the Avenger EFI system onto a ’61 Corvette that was being built as a performance street vehicle. One of the first things Green had to do was create a fuel return line for the system. Fuel injection systems provide constant pressure to the injectors, and a return line ensures that the system doesn’t get starved (vapor lock) or over pressurized with fuel.

Green used Earl’s AN-8 stainless steel braided fuel hose that would eventually attach to the outlet of the throttle body and connect to a hard stainless steel line he bent, which runs alongside the frame. The line feeds into another braided piece of fuel hose that goes back into the tank. In this case the Corvette uses a fuel cell located in the trunk and has AN fittings for both a fuel inlet and return line already on it. If you have an OEM fuel tank, you can simply purchase a return line adapter that fits between the rubber filler neck of the tank. Moroso makes a nice one (PN MOR-6535) that’s made from aluminum tubing and retails around $40.

Holley’s Avenger EFI system comes with a high-pressure inline fuel pump that must be adapted to your vehicle’s existing fuel line. In this case, the Corvette already had an electronic pump with a separate regulator. Green removed both and replaced them with the new Holley electric pump supplied in the kit. After finding a suitable location away from the exhaust, he mounted the new pump to the frame using the isolator clamps provided in the kit. A fuel filter is also included, and Green plumbed it all together using stainless braided hose and the appropriate AN-8 fittings. Once he was done, both the fuel line and return line now run directly from the fuel cell, along the inside of the frame and up to the throttle-body.

The engine in this application was a 427ci small-block stroker that was outfitted with a four-barrel carburetor on top of a Weiand Street Warrior dual-plane intake manifold. Swapping it was only a matter of unbolting the four-barrel carburetor and bolting on the new Holley TBI unit. The fuel inlet hose was attached to the rear of the throttle-body, which already has a pre-adjusted fuel pressure regulator. The new fuel return line was then attached to the outlet on the throttle body that leads back to the tank.

Because there were slight differences between the size and shape between the old carburetor and the new Holley throttle-body, Green had to make minor adjustments to the Corvette’s throttle linkage for it to work properly. Once this was done, the various sensors in the kit were installed and connected to the computer’s wiring harness. These included the Manifold Absolute Pressure Sensor, Idle Air Temperature Sensor, and Throttle Position Sensor. You’ll also have to make a hole in your exhaust system for the Oxygen Sensor. The kit comes with a small bung that must be welded onto your exhaust, allowing you to screw the O2 sensor into position. The instructions will tell you the best location along the exhaust to make this modification, and Green followed its advice and attached it as close to the header collector as possible.

The system also comes with a Water Temperature Sensor that can be installed into the threaded hole typically used for the water temperature gauge-sending unit. You can use the tapped hole in the manifold for the new sensor, but if you need it for your gauge you can use a T-fitting to operate both. Once all the sensors are installed, the main control unit needs to be routed and plugged into the harness.

The ECU that operates the EFI system should be mounted in a location away from heat. This can vary depending on your vehicle and any accessories you have on it. Green built a small panel that allowed the ECU to tuck away neatly inside the inner fenderwell of the Corvette, between the passenger wheelwell and firewall. Since the Corvette will have aluminum panels covering the inner fenders, this made a safe location to protect the ECU from heat and moisture. No matter where you decide to mount your ECU, Green recommends trial fitting everything first.

The wiring harness also has separate power leads to operate the hand-held tuner and the fuel pump relay. You can take a 12V key-on ignition source from your Chevy’s fuse box and attach another lead directly to the battery. A system like this one also has provisions to use with various types of ignition sources. The Holley unit uses an ignition trigger for the injectors. So it’s wise to read the instructions carefully to see all of the scenarios available and wire the trigger lead according to which type of ignition system the vehicle is using. In this application, the Corvette had an MSD Digital Ignition box, which provides an ignition trigger on the side of the unit. This made it easy to wire the fuel injection trigger lead directly into the box.

Once everything was wired and plumbed, Green turned the ignition key and the LCD display on the hand-held turner turned on. It features a simple menu, allowing you to select approximate engine size, horsepower, transmission, and other basic variables of your application. If you’ve ever installed a power programmer onto your late-model vehicle, you can easily operate the Holley unit. Once the selections were made for this particular Corvette, Green turned the ignition to the “on” position and made sure there weren’t any fuel leaks. Then he cranked the engine over and it started without any hesitation. The Holley ECU automatically fine-tunes the fuel and ignition timing to the engine and also takes into account your driving habits to optimize fuel delivery.

The total time it took to install in this application was about six hours. But no laptop or additional tuning on the dyno was needed. It will be a while before the Corvette gets back on the road and to the track, but judging from the smooth idle from this 500hp street engine, we bet it will perform admirably on both the street and strip. Holley also makes a similar self-tuning system in a multiport fuel-injection design that is available for a variety of engine sizes and applications. But the Avenger EFI system is probably the easiest to install, and can really make a difference in improving your Chevy’s power and fuel economy in a matter of hours.