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No-Carb Diet

Edelbrock's Pro-Flo Multi-Point EFI System Eliminates the Carburetor!

Rob Wallace III Sep 30, 2004

Many years ago, as the muscle-car era came to a close due to federal regulations on air pollution and fuel economy, it was widely believed that high-performance automobiles were history.

And then along came electronic fuel injection. Computer management that can regulate every aspect of an engine's operation to the millisecond has put the pep back into the Chevy V8. The everyday power, efficiency, and drivability of today's EFI engines was beyond imagining 25 years ago.

It has become quite popular these days to swap late-model EFI motors like LT1s, L98s, and even the occasional Gen-III LS1 into older Corvettes in order to make the classics more drivable. But what if it weren't necessary to perform an entire engine transplant in order to enjoy the benefits of modern electronic fuel injection? Well, Edelbrock Performance Products has designed their Performer and Performer RPM Pro-Flo EFI systems to allow anyone to retrofit a multi-point EFI system onto their pre-1986 carbureted small-block (or big-block) Chevy V8.

The Edelbrock Pro-Flo EFI system is a complete induction package that includes everything needed to convert an older carburetor motor to electronic fuel injection. The Performer Pro-Flo system has a 2V air valve design that's capable of flowing 750 cfm, includes fuel injectors rated at 29 lbs-hr, and is designed to easily handle up to 350 hp. It uses a speed-density engine management system to control fuel and spark based on engine speed and engine load. Their Performer RPM Pro-Flo EFI kit is designed for even more extreme performance, and is rated up to 435 hp. Edelbrock has even incorporated a self-contained electronic calibration module for the ECM that allows you to adjust the Pro-Flo system parameters yourself without a laptop computer.

We decided to try out a Performer Pro-Flo EFI system (P.N. EDL-3503) on a basically stock '81 Corvette driver with a four-speed and 74,000 miles. Our friends Scott Arnold and Mike Tilton at Scotty's Vettes in Dickens, Texas, led us through the installation, which is fairly straightforward considering it requires modifying the fuel system, induction system, and ignition system. Again, Edelbrock includes everything needed to make the EFI conversion possible.

The improvements we saw in the '81 were dramatic. To begin with, it was your average, semi-anemic, 190hp low-compression late-smog-era Shark that suffered from sluggish throttle response, temperamental starting, and mediocre fuel economy. After installing the Edelbrock Pro-Flo EFI system, the '81 suddenly responded with crisp acceleration, great starting, and a noticeable improvement in mileage. The only downside to the Edelbrock Pro-Flo EFI system is that it does not accept stock emissions control systems, and therefore is not legal on Vettes that are still pollution-controlled.

Though we were unable to perform baseline testing ourselves due to time constraints, the December 1981 issue of Car & Driver tested a new '81 Vette, with results of 0-60 mph in 7.2 seconds, 0-100 mph in 19.7 seconds, and the quarter-mile in 15.4 seconds at 91 mph. Using an accelerometer after installing the Edelbrock Pro-Flo EFI system, we measured acceleration at 0-60 mph in 6.12 seconds, 0-100 in 16.4 seconds, and 14.7-second quarter-mile times at 96 mph. Beyond that, C&D in 1981 observed the Corvette's top speed at 130 mph, but we achieved 129 mph with plenty of pedal left to work. All while averaging 16-19 mpg around town and 22-24 mpg on the highway after several fill-ups. Not half-bad for an old Shark!


Edelbrock Pro-Flo Multi-Point Electronic Fuel Injection Kit, PN 3503.

After disconnecting the negative battery cable, emptying the fuel system, and draining the coolant, Scotty begins by removing the stock air cleaner assembly along with all of its connectors and ducting.

The stock HEI distributor must be removed and converted into a Multi-Port Fuel Injection-compatible Hall effect electronic distributor. Before he removes the cap, however, Scotty marks its position for reference.

Scott disconnects the fuel line, the throttle linkage, and everything else connecting the carburetor.

This motor is now carb-free!

With the carburetor gone, Scotty now has plenty of access to the distributor. He carefully notes the position of the rotor and marks the distributor housing where the rotor points to Cylinder No. 1, then releases the drive gear and shims, and removes the rotor and distributor shaft.

After Scotty disconnects the upper radiator hose from the thermostat housing, he unbolts the pulley from the smog pump and 86s the entire smog pump assembly, brackets and all. It is incompatible with the new EFI system and therefore will not be used again.

Next, he unbolts the valve covers, taps each cover a rubber mallet to break the seal between them and the heads, and pulls the valve covers free.

The intake manifold is next to get removed. It is the last piece of the stock induction system that we'll need to replace for our EFI conversion.

Now for the fun part. Scotty lays cloths over the lifter valley and plugs the ports, then he and Mike begin the tedious chore of scraping the old gasket residue off the head surfaces. Then scraped clean, they remove the coverings, vacuum up any remaining scraps, and wipe the surfaces clean with lacquer thinner.

Once the head surface is clean and smooth, Scotty applies the new gaskets, lays a bead of Loctite 598 High Temperature Silicone Gasket across each end seal surface and around water passages on the head surface, then he sets the new Edelbrock intake manifold assembly in place.

Once the intake manifold is properly positioned, Scotty applies Teflon thread sealer to each of the manifold bolts and hand tightens them all. Then he goes back and, in a specific sequence starting at the center and working outward, carefully torques the bolts down to 25 ft-lbs.

After replacing the valve covers, Scotty installs a new 180-degree thermostat. This will help the Shark run cooler during hot Texas summers, but is just warm enough to prevent it from sticking in a cold start mode and not performing properly.

Scotty reinstalls the original throttle linkage, but he finds it necessary to cut and grind the end off of this bracket to make it work with the new intake.

Once all of the throttle linkage and springs, transmission, and fuel lines are re-connected, Scotty checks all of the linkage for smooth operation throttle operation from idle to wide-open-throttle.

With the induction end of the motor put together, Scotty turns to converting the stock HEI distributor into an EFI-compatible Hall effect electronic distributor. It's necessary to completely disassemble the distributor, removing all the internal components from the housing, including the vacuum advance diaphragm.

Once the distributor is completely gutted, Scotty installs the electronic Hall effect sensor and sensor plate, shown here. Then he will install the new shutter wheel on the bottom of the rotor mounting plate from the drive gear end of the rotor shaft before re-installing the distributor shaft into the distributor.

When the distributor was fully reassembled, Scotty hand-turned the rotor several times to verify the proper alignment and the right clearance between the shutter wheel teeth and sensor. Satisfied, he placed the rebuilt distributor into the motor and re-installs the cap.

Next up, he attaches the included Edelbrock P.N. 3518 Ignition Amplifier to the firewall on the driver's side.

With the Vette on a lift, Scotty cut a 1/2-inch hole in the passenger-side exhaust down tube, just downstream of the collector flange, and welded the provided bung fitting for the O2 sensor to it. After coating the sensor threads with a high-heat anti-seize compound, Scotty threads the O2 sensor into the fitting.

While the car is still in the air, Scotty splices into the fuel line to install the in-line high-pressure electric fuel pump. After cutting away a section of hard line roughly underneath the passenger door, he routes the power wires through the gap in the frame rail that the original fuel line ran. For the pump to flow in the proper direction, the electrical connectors should face the front of the car.

Scotty uses some of the included 3/8-inch high-pressure rubber fuel line to connect the fuel pump to the factory fuel line, connects the power wires, wraps the pump in insulating foam, and clamps the finished assembly to the frame rail. The pump needs to be at or below the level of the fuel tank.

Edelbrock includes many feet of 3/8-inch high-pressure rubber fuel hose to be used as the primary fuel line. Scotty next attaches one end of the 3/8-inch fuel line to the driver's side fuel rail on the intake manifold.

He carefully routes the primary fuel line around the engine compartment in the safest manner possible, being sure to avoid kinks, sharp objects, and excessive heat.

Scotty fits the included fuel filter into the primary fuel line, and attaches it to the passenger-side of the engine compartment, near the coolant reservoir. Mounting the filter between the fuel pump and the motor allows the fuel to be pushed through--rather than drawn through--the fuel filter.

The Pro-Flo EFI system requires high and constant fuel pressure and volume, so the fuel pump delivers more fuel than the motor needs at any given point. Thus, the fuel that bypasses the injectors is returned to the tank via a return fuel line. Scotty connects the supplied 5/16-inch ID rubber bypass return line to the Pro-Flo fuel pressure regulator on the fuel rail.

All that's left now is the electricals, so Scotty opens up the electronic control module to install the computer chip needed to operate the ECM. Edelbrock calibrates the chips for the particular parameters of each car, so the Pro-Flo fuel-injection system is shipped without the computer chip, and Edelbrock second-day airs a properly calibrated chip to consumers free of charge.

With the ECM's cover removed, it's a simple operation to install the chip. Just be careful not to touch or damage any of the vital electronic components within the ECM.

Next, Scotty drills a 1 3/4-inch hole in the trans tunnel, very close to the firewall. Then he and Mike work together to feed the fuel pump relay, the ECM connector, and the Calibration Module relay from the main wiring harness in the engine bay through the tunnel and into the passenger compartment.

The compact design of Edelbrock's ECM unit allows for some creative placement. Scotty finds the perfect location in a late Shark to be on top of the trans tunnel under the console. Once the ECM is mounted, Scotty plugs in the ECM connector.

Scotty has also found that the Edelbrock calibration module, which allows you to tune the EFI system any time without a laptop, is conveniently sized and shaped like an old eight-track. He removes the inner liner of the '81 glove box, drills a small hole in the bottom to run the wire through, and quickly has an ideal spot to store the calibration module.

With the computer wired in, Scotty completes the installation by plugging in the injector connectors, shown here, and all the sensors and other electrical devices into the main wiring harness. The harness and connectors are straightforward and are easily connected using factory-style plugs.

Finally, Scotty has switched to a low-profile after-market air cleaner to guarantee there are no clearance issues between the hood and the slightly-taller-than-stock intake. He drilled a 3/4-inch hole in the air cleaner base, inserts the EFI manifold air temperature sensor grommet, and slides the MAT sensor into the grommet.

Ta-da! The final results not only include a big improvement in performance, economy, and drivability, but the Edelbrock Pro-Flo EFI system also cleans up the engine's looks quite a bit too!


Scotty's Vettes
Dickens, TX 79229

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