Chevy Truck TBI To EFI Conversion
How To Bolt On 25 Hp And 35 Lb-ft Of Carb-Approved Performance To Your '87-'95 5.7L TBI Small-Block Hauler
From the December, 2004 issue of Sport Truck
By Barry Kluczyk
Photography by Brian Reese
Here's the out-of-the-box...
Here's the out-of-the-box layout of the Edelbrock EFI kit for our '95 Tahoe. It includes the manifold, hoses, fittings, and wires necessary to complete the swap. Making the job simpler is the preassembled manifold, which comes with eight pico-style (short) fuel injectors, CNC-machined aluminum fuel rails, fuel crossover line, and fuel pressure regulator already installed. The only items missing (in our opinion) are the manifold gaskets and a tube of RTV sealant. By the way, the kit is emissions-legal and carries a CARB-exempt number.
As automotive technology has evolved, so has the performance world. And though carb and intake manifold swaps haven't disappeared altogether, the proliferation of fuel injection has certainly made them more rare.
We were reminded of the simpler days of induction when we got a look at Edelbrock's Performer EFI multipoint port fuel injection system. Of course, the Performer name is an old one in the world of intake manifolds, and the appearance of the EFI system's manifold looks like a high-rise single-plane intake for a two-barrel carb.
Edelbrock's system is designed to accept the throttle body of GM TBI-equipped engines (there are different systems for '88-'92 and '93-'95 engines, as well as big-block 7.4L engines), but replaces the two stock fuel injectors with eight port-mounted pico-style injectors. The stock TBI setup uses the two injectors in the air valve and sprays downward toward the throttle blades.
Like other OE port injection systems, Edelbrock's CARB-approved multipoint system uses a single injector for each intake port, spraying fuel more directly into the cylinder head. Edelbrock's claims of superior performance, driveability, and fuel economy compared with a throttle-body design are the very reasons most auto manufacturers have embraced port fuel injection. In fact, the Vortec line of GM truck small-blocks that debuted in 1996 featured port fuel injection, as do today's LS1-based engines.
Unfortunately, the Chevy Tahoe that goes under the knife in this story was screwed together just a year too early. It's a '95 model, equipped with the LO5 350-cid small-block. That means TBI and just 205 hp from the factory. Owned by SLP Performance Parts' chief engineer, Brian Reese, the 100,000-mile truck had already been perked up with the addition of a custom cold-air intake, headers, after-cat exhaust, and 180-degree thermostat - all taken off the company's shelves (it, uh, was a research project).
A set of Comp Cams' 1.6-ratio roller rockers and a custom Hypertech power chip were added, too. With all those bolt-on goodies, the previously tepid Tahoe's rear-wheel output (measured on the Dynojet at New Jersey's Cartek Racing) jumped from 149.3 hp and 250.5 lb-ft of torque to 175.5 rear-wheel horses and 301.3 lb-ft - a significant 18.6 percent improvement.
For the sake of curiosity - not to mention, the nagging quest for more performance - Reese wanted to give the Edelbrock EFI kit a try. Figuring it was better to let someone ruin his own vehicle, rather than one of ours, we told Reese to go for it. And, what the heck, if the truck ran afterward, we'd cover the swap in the magazine.
As it turns out, we need not have worried. The Edelbrock EFI system was very complete and the installation was straightforward. That's not to say it wasn't complicated, though. There are a few tricks to the install and not every part needed for it is included with the kit.
Here are some of our notes since the project's completion. Keep them in mind if you're contemplating a similar swap:
The computer's PROM chip must be replaced. Doing so requires the buyer to fill out an information card with information found on the vehicle's RPO sticker and ECM computer. The card must be sent to Edelbrock, which sends the new chip. The round-trip service for our Tahoe took six days.
We were lucky: Our '95 truck did not require a new fuel pump. However, anything other than a '95 Tahoe requires an upgraded pump. On SUVs, that means dropping the tank. On pickups, you'll be removing the bed. Edelbrock offers the higher-capacity pump, but it's an extra-cost item for the project.
Two items not included with the kit are intake manifold gaskets and RTV sealant. Minor items, yes, but you'll really miss them once the old parts are removed and you don't have a ride to the auto parts store. Stock up before you begin the project.
There's a gasket included with the block-off plate for the fuel inlet/outlet positions on the throttle body. In our opinion, the plate seemed a little too thin and flexible, and we could see daylight around the gasket after it was installed. We decided to remove the gasket and use a healthy dollop of RTV instead.
The kit's fuel line push-on connectors were very tough to push together. How tough? We needed a vice and lube to squeeze them together.
In all, it took about eight hours to complete the installation. And while our hands were dirty (well, while Reese's hands were dirty), we decided to replace the engine-driven fan with an electric unit from Flex-a-lite. With the previously installed 180-degree thermostat, the fan not only improves cooling, but its adjustable thermostat allowed us to dial in the truck's cooling needs.
When all the work was completed, it was back to Cartek Racing for some follow-up runs on the Dynojet. With simply the injection swap and new fan, the Tahoe's peak output at the rear wheels jumped from 175.5 to 197.9 hp. Torque leaped from 301.3 lb-ft to 313.4 lb-ft at the tires.
More telling, however, was the new injection system's performance across the powerbands. Although peak horsepower jumped more than 22 hp, it occurred at just 2,700 rpm. As the tach edged higher, the difference between the stock TBI setup and Edelbrock's EFI system was more pronounced. By 3,700 rpm, the new setup was producing 194 horses, a 25.2hp gain over the TBI's 168.8 ponies at the same rpm.
The same goes for torque. By 3,100 rpm, the Edelbrock-fed 350 made 28-35 lb-ft of torque more than the TBI setup through 4,100 rpm. This is especially helpful on the street, as the torque curve starts to head south on the motor by 3,100 rpm. While it doesn't reverse this trait, the Edelbrock system nonetheless props up the engine's pulling power to the redline. (We suspect some of the horsepower and torque gains came from the removal of the engine-driven fan, too, which reduced some parasitic drag on the engine.)
Edelbrock's EFI system retails for about $1,000. In our experience with the Tahoe, we think it offers good bang for the buck - not only in outright performance, but overall driveability as well. Yes, the install is more complicated than the old carb and intake swap. But, hey, there's no need to tinker with a inicky carburetor afterward.
For 25 horses and 35 lb-ft at the tires, we'll gladly put up with a little complication.
1. The project starts with...
1. The project starts with the removal of the stock throttle body and intake manifold. Be careful when removing the throttle body, as it will be reused. There are two fuel lines at the rear of the throttle body, and care should be taken when disconnecting them, as fuel line pressure can be very high.
2. Next, the distributor was...
2. Next, the distributor was removed, but not before its original position was marked on both the distributor and another reference point. A mark on the firewall makes a good reference point. (Remember: You won't want to mark the manifold as a reference, as it will be removed and discarded.)
3. With the distributor and...
3. With the distributor and throttle body removed, the stock intake manifold can be carefully pried and lifted out of place. The fuel lines are also removed at this point, as they'll be replaced by new ones supplied in the Edelbrock kit.
4. With the stock manifold...
4. With the stock manifold on the bench, the sensors and fittings that can be reused on the Edelbrock manifold need to be transferred. Notice that the Edelbrock manifold is more than an inch taller than the stock intake. The other obvious visual difference is the Edelbrock's single-plane design, while the stock manifold features a dual-plane design.
5. With the mating surfaces...
5. With the mating surfaces of the heads carefully scraped of old gasket residue (razor blades work best), the new head gaskets are installed and the new manifold is ready to be dropped into place.
6. Once the new manifold is...
6. Once the new manifold is torqued to spec, a number of other components are bolted to it, including a new Edelbrock-supplied throttle cable bracket. The distributor can also be reinstalled at this point. We were lucky here: Early TBI engines used an angled water neck that interferes with the EFI system (requiring a swap with a later-model water neck). Our '95 engine was fine.
7. On the stock manifold,...
7. On the stock manifold, the canister purge solenoid is mounted on the two thermostat mounting bolts. With the Edelbrock manifold, the solenoid is moved to an aluminum spacer located above the thermostat housing. To mount the bracket in its new location, one of the stock mounting holes must be trimmed off.
8. With the new manifold in...
8. With the new manifold in place (including heater and radiator hoses), attention is turned to the conversion of the stock throttle body. It begins with the removal of the fuel inlet and return fittings. (The photo depicts the bottom of the throttle body.) Some vehicles have a throttle valve for transmission kick-down. Again, we lucked out: The '95 didn't come with the throttle valve, so it was one more step in the instructions we could skip.
9. With the stock fuel inlet...
9. With the stock fuel inlet and outlet fittings removed, an injector block-off plate is required. Although a paper-style gasket for the plate is included with the kit, SLP's Brian Reese didn't feel comfortable with its sealing capability - daylight could be seen between the plate and throttle body after installation. Reese removed the plate and gasket, and laid down a bead of RTV in the gasket's place.
10. Here's the modified throttle...
10. Here's the modified throttle body, including the RTV-sealed block-off plate, ready for reinstallation. The stock fuel inlet and outlet aren't necessary, as the incoming fuel will go directly to the fuel rails and injectors. Although no longer adding fuel, the throttle body still serves as the regulated source of incoming air for the engine.
11. There's a new wiring harness...
11. There's a new wiring harness for the injectors that is included with the kit. It needs to be installed so that the wires are routed to the rear of the manifold. Although the wiring seems cumbersome, the supplied instructions walk the installer carefully through each necessary cut, crimp, and splice.
12. All done. The new injection...
12. All done. The new injection system looks downright OE in the Tahoe's engine compartment. We lucked out once again when it came to the fuel system. All other applications - save the '95 Tahoe - require the installation of a higher-capacity in-tank fuel pump. This would have otherwise meant dropping the tank for the swap (or removal of the bed for pickups). Nonetheless, we still had to install some new fuel lines, and the supplied #6 Pushlock fittings required a Herculean effort (and a vise) to connect. As for initial start-up, it took a couple of tries, but the engine fired up and idled smoothly. Setting the timing first required the disconnection of the ignition interrupter wire (located beneath the dashboard). Once tuned, the engine produced 197.9 rear-wheel horsepower and 313.4 lb-ft of torque, up from 175.6 horses and 287.7 lb-ft. Not too bad, we think. Dyno runs were performed at Cartek Racing in New Jersey.
13. Electric Fan Installation...
13. Electric Fan Installation
More horsepower means more heat, and since our Tahoe test truck was definitely making more power, we felt it could benefit from some added cooling capability. A call to Flex-a-lite brought the company's Model 250 fullsize truck fan, which boasts a lightweight fiberglass shroud, two fans, an adjustable thermostat, and an adjustable A/C relay. The fan's installation should free up some horsepower, too, thanks to the loss in parasitic drag from the engine-turned fan.
14. We started by removing...
14. We started by removing the stock fan. Compared with the tight confines of some cars we've worked on, it's downright roomy working on the Tahoe's fan.
15. Side by side, it's pretty...
15. Side by side, it's pretty easy to see that the Flex-a-lite's twin 14-inch fan system should provide plenty of extra cooling. Flex-a-lite claims the fan system will pull 5,200 cfm. Our fan setup was for a 17-inch-core radiator (measured top to bottom)
16a. The universal bracket...
16a. The universal bracket supplied with the kit is adjusted to fit the mounting points beneath the Tahoe's hood. The bottom "feet" of the bracket will attach to the lower radiator crossmember. The upper end of the bracket will require some nylon ties to secure it to the top core support.
17. The temperature sensor...
17. The temperature sensor that signals the fans to turn on requires insertion between the radiator and radiator hose. The bulb end of the sensor goes into the radiator, while the sensor tubing must be carefully bent to follow the contour of the inlet housing. The radiator hose will cover the tubing as it is tightened against the inlet housing.
18. The last major step was...
18. The last major step was to mount the control box for the fans and connect all the necessary wiring. In all, it's an easy installation that almost any enthusiast can handle in his driveway or garage.
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