Electronic Fuel Injection Corvette Conversions - EFI Your Small-Block!
Fuel Injection Made Easy From FAST
From the October, 2006 issue of Corvette Fever
By Steve Dulcich
Photography by Steve Dulcich
Converting an engine originally equipped with a carburetor to electronic fuel injection (EFI) is nothing new; though every year it seems as if interest in taking the EFI plunge gains momentum. OEM vehicles of the past two decades have firmly engrained the advantages of fuel injection to all but the most diehard enthusiasts. Far be it from us to suggest taking a show-bred Corvette and altering it in such a way. however, if serious road time is more important than originality in your Vette escapades, retrofitting to EFI is a modification worth considering. Late-model performance cars, such as the C5 and C6, provide all the evidence necessary to show the attributes of injection, including flawless drivability and remarkable reliability. Wouldn't it be nice to take some of that technology and apply it to an earlier carbureted Corvette?
For the vast majority of enthusiasts, the thought of running a custom aftermarket EFI system is filled with trepidation. Sure, it seems to work great on modern cars, but just what is involved in setting up an older engine to work with this modern technology? At first glance it might seem pretty complex, with items such as the wiring, sensors, the control box, and so on. In comparison to that old Quadrajet, it certainly involves more hardware and at a more sophisticated level, but breaking it down is nothing a seasoned wrench-turner couldn't handle. We sought just such a conversion to a small-block Chevrolet engine and found the changeover less daunting than anticipated, using components from FAST.
The basic hardware change...
The basic hardware change when making the move to EFI is the intake manifold, which isn't terribly surprising since we are talking induction systems here. One of the key components is the intake manifold, and there are a myriad of choices. There are purpose-built EFI manifolds available from the aftermarket, and some available with EFI bosses cast in, which need machining to accept the injectors. Manifolds originally intended for carbureted applications can also be readily adapted, as evidenced by our own Edelbrock Victor Jr. Note the injector bungs TIG welded to the runners on this intake. The universal bungs are available from FAST.
Back in the early days of EFI conversions, most efforts centered upon adapting the primitive OEM components of the time to vintage iron. Installing the hardware was simple enough, but the difficulty stemmed from gaining control of the tuning parameters. Such installations nearly always involved modifications to the factory specifications, and the control units that provided the logic to run the systems were notoriously inflexible. Times have changed, and these days companies like FAST do the work to produce components that have been designed to work together, in a wide range of potential applications. the technology is built into the system, so the end user does not need to be a fuel-system engineer. The software facilitates tuning the system to an unbelievable degree, making such installations flexible in controlling a wide range of likely combinations.
Whether you are looking to inject an older Corvette cruiser, or are looking to plant a modern, fuel-injected monster in your radically modified C3, the systems to make it happen have already been ironed-out to the nth degree.
Supplying the fuel to the...
Supplying the fuel to the injectors is the fuel rail. Some means of holding the rail at a fixed distance to the manifold is required to keep the rail/injector assembly in place on the intake manifold. This manifold was tapped to accept simple brackets at each end of the rail. There are many specialty shops that can perform all of the modifications required to convert an intake to EFI for a custom installation, including FAST fuel injection. Holley, Edelbrock, and others have off-the-shelf intakes designed to accept rails and injectors.
An EFI throttle body will...
An EFI throttle body will have a device called an idle air controller (IAC), which takes care of the idle functions of the engine. Basically, an electrically operated motor opens and closes a small air passage through the throttle body that provides the engine with the air requirements for idle. The IAC can continuously adjust the idle settings, attempting to make it perfect at all times under varying conditions. In contrast, a carburetor just has the throttle blades hung open a fixed amount by the idle speed screw.
EFI injectors are a slip-fit,...
EFI injectors are a slip-fit, and seal via o-rings. The key to injector selection is sizing, designated in lb/hr of flow. The key to sizing is to make sure the injectors flow enough fuel for the max power the engine will be capable of. FAST's tech line can provide injector flow rates based upon the maximum anticipated power output.
In an EFI system, we find...
In an EFI system, we find a throttle body in the location normally occupied by the carburetor. The throttle body only meters the air flow into the engine, and handles none of the fuel.
Is there EFI in the future of your seasoned Vette? It's pretty hard to ignore the drivability of modern systems that continually adjust the fuel and spark to their optimal settings as you drive. Equipped with modern controls, you're practically rolling down the road with an ace tune-up man wrenching away under the hood at all times. An expertly calibrated fuel-injection system can eliminate the temperamental nature that some carbureted installations can exhibit, and make driving the pleasure it was intended to be. Everything you need is readily available from EFI specialty companies such as FAST, so what are you waiting for?
Serving as the "brains" of...
Serving as the "brains" of an EFI system is the electronic control unit. The new FAST XFI box is a state-of-the-art aftermarket engine control system with greater flexibility and more user-friendliness than ever before. Changes to the hardware and accompanying software expanded the capabilities of the system, allowing control over the full spectrum of engine fuel and timing functions, as well as auxiliary outputs to control a variety of additional devices, including everything from torque converter lock-up to fan actuation. Multiple LED's on the FAST XFI box confirm inputs from crank, cam (if applicable), ignition trigger, and power, while a second series shows cylinder firing output.
|Difficulty Index ::: |
|ANYONE’S PROJECT |no tools required || 1 |
|BEGINNER |basic tools || 11 |
|EXPERIENCED | special tools || 111 |
|ACCOMPLISHED | special tools and outside help || 1111 |
|PROFESSIONALS ONLY | send this work out || 11111 |
Carb vs. EFISuperflow 901 Engine Dyno Tested at Westech Performance Group STP Correction Factor
Any electronic brain needs...
Any electronic brain needs information on what is going on at the engine to decide what output parameters to send to the ignition and fuel systems. the engine sensors accomplish this. At the throttle body, we have the throttle position sensor, which simply informs the XFI box how deep you've stabbed the go pedal. Hook-up to all the sensors is simplicity in itself-it just plugs in and is clearly labeled.
Another temperature sensor...
Another temperature sensor is the inlet air temperature sensor (IAT), which makes the XFI control unit aware of the temperature of the air entering the engine. Air density changes with temperature, and the IAT sensor lets the ECU know the conditions at all times. Typically, this sensor is put into the air cleaner or elsewhere in the air inlet stream to the engine.
Another one of the key sensors...
Another one of the key sensors is the coolant temperature sensor. It simply screws into the water jacket at a convenient point (in this case, the intake manifold) and provides the engine temperature information to the XFI control box.
It is important for the control...
It is important for the control unit to know the load being placed upon the engine at all times. The manifold air pressure (MAP) sensor provides this information. Essentially, this sensor reads manifold vacuum, with lower vacuum equating to higher load. Hooking up the MAP sensor is as simple as running a vacuum line from the manifold or a point below the throttle plates on the throttle body to the MAP sensor, and then plugging in the harness connection marked MAP.
|RPM ||EFI ||CARB |
|3,000 ||352 ||339 |
|3,200 ||343 ||336 |
|3,400 ||340 ||339 |
|3,600 ||346 ||347 |
|3,800 ||354 ||356 |
|4,000 ||357 ||360 |
|4,200 ||367 ||362 |
|4,400 ||377 ||375 |
|4,600 ||379 ||382 |
|4,800 ||382 ||388 |
|5,000 ||388 ||390 |
|5,200 ||386 ||390 |
|5,400 ||389 ||390 |
|5,600 ||386 ||387 |
|5,800 ||380 ||381 |
|6,000 ||371 ||369 |
|6,200 ||363 ||362 |
|6,400 ||344 ||347 |
In an EFI system, the ignition...
In an EFI system, the ignition advance function is handled totally electronically, so the advance functions of the distributor must be rendered inoperative. We used a MSD distributor, which is readily locked-out-meaning the timing is mechanically fixed. Most distributors can be modified to eliminate the advance functions.
Virtually any OEM distributor...
Virtually any OEM distributor can be used with the FAST XFI fuel-injection control unit, as well as the popular aftermarket units such as our MSD unit. A conventional distributor will allow batch-fire of the injectors. A sequential system follows the firing order with the injector pulse on a cylinder-by-cylinder basis. To time a sequential system, a cam-position signal is required so that the control unit has a reference of which cylinder is firing. A dual-sync distributor is needed for this cam reference signal. MSD and Mallory (among others) manufacture distributors with this feature, while FAST is tooling up for a full line of dual-sync distributors. We ran a simple batch-fired system on this small-block Chevy, using a locked-out conventional distributor combined with a MSD ignition system. Batch fire worked well, and testing showed very little appreciable advantage to sequential. though with the dual-sync distributor, a sequential system can be easily accommodated if desired. The MSD points signal is wired to the XFI controller to provide the rpm signal.
A valuable feature for any...
A valuable feature for any aftermarket EFI system is the ability to run in closed loop, which means the mixture (air/fuel ratio) is monitored continuously, and the processor makes continuous minor adjustments to the injectors to keep the ratio in the targeted zone. A wide-band Lambda sensor creates a signal that corresponds to the air/fuel ratio at any instant, and the XFI control unit follows with near-instant adjustments. EFI can also be run in Alpha-Numeric mode, which means open-loop, where the fuel delivery at the injector is strictly controlled by preprogrammed fuel maps. Street or street/strip performance cars really benefit from closed-loop capabilities.
EFI requires a different fuel...
EFI requires a different fuel system than that used in a carbureted application because of the much higher fuel pressure. Typically, injectors are rated for flow at 45 psi. That is the normal pressure setting used with a FAST system and is best set using a bypass regulator. A pump that can provide sufficient pressure is a must, and it also must flow the required volume for the power output of the engine. FAST's tech help can provide sizing information on both the fuel-system components and the injectors themselves. Size and capacity has to match the application, based on anticipated power output.
|RPM ||EFI ||CARB |
|3,000 ||201 ||193 |
|3,200 ||209 ||204 |
|3,400 ||220 ||219 |
|3,600 ||237 ||238 |
|3,800 ||256 ||257 |
|4,000 ||272 ||274 |
|4,200 ||294 ||290 |
|4,400 ||316 ||314 |
|4,600 ||332 ||335 |
|4,800 ||349 ||355 |
|5,000 ||370 ||371 |
|5,200 ||382 ||386 |
|5,400 ||400 ||401 |
|5,600 ||412 ||412 |
|5,800 ||420 ||421 |
|6,000 ||423 ||422 |
|6,200 ||428 ||428 |
|6,400 ||419 ||423 |
Carburetion Vs. Injection
Converting to EFI is not a decision that should be based upon looking for outrageous power gains, but rather for the best drivability and efficiency gains possible. The naked truth is, given exactly the same components, the power of a perfectly tuned carburetor will be virtually identical to an EFI system. One of the key differences is an EFI system is "smart" and once programmed correctly, will always be in perfect tune, no matter how the operating conditions of temperature and air density changes. We installed a Demon four-barrel carburetor to the tuned EFI system on the dyno just to compare the wide-open-throttle output. Not surprisingly, with the combination otherwise identical, the power curve was virtually unchanged, with the EFI gaining a modest advantage in low-speed torque. However, by taking advantage of the intake manifold design flexibility available when running EFI, the power characteristics can be changed significantly. Modern plenum ram manifolds of the type used on the LS-family of engines are a good example. This design takes positive advantage of inertia ram tuning for a healthy boost in torque, but such a manifold layout would be impossible in a carbureted application.
While an EFI system can be tuned to a fine set of parameters at the keyboard of a computer, a carburetor is a mechanical device with fuel curve adjustments primarily handled by changing jets, altering the orifice restricting fuel flow. Tuned for a perfect air/fuel ratio, output is about equivalent when considering full-throttle horsepower and torque, if all else in the engine remains unchanged.
FAST's XFI system comes with...
FAST's XFI system comes with a harness that has all the required terminal connections to plug right in and run the engine. To recap, we have sensor connections to the TPS, IAT, CTS, and Lambda (O2) sensors. The IAC is plugged in at the throttle body; an rpm wire is connected to the ignition; the eight injectors are plugged in; and the power and ground wires are connected. The system comes with an internal diagnostic check and LED readouts that confirm all the required hook-ups are functioning. The harness is clearly labeled, making it a snap to wire up the injection system.
Our small-block was mounted...
Our small-block was mounted to the dyno to test and run the engine with the FAST XFI, though the conversion to fuel injection can be installed and tuned in the vehicle. With the XFI, fuel and spark parameters are already programmed in with base settings, putting you in the ballpark as far as getting the engine fired and running. The simple setup menus let you fill in the blanks for the engine's combination and components. Various specifications such as engine displacement, injector flow rating, number of cylinders, and so on are typed in, and then the operational parameters, (e.g., whether the injection system will be run bank-to-bank or sequentially) are inputted. Westech's dyno operator, Steve Brule, quickly had our 350 small-block up and running.
The FAST XFI comes with a...
The FAST XFI comes with a well thought out software package and is connected to a computer for tuning with a communication cable. Engine and sensor functions are all monitored and can be recorded, with key information available on the tuning screen via the dashboard functions. The FAST system also has useful data-logging capabilities. Once the engine is up and running on the provided base maps, fine-tuning dials it in. Here, Westech's Steve Abbruzzese is making changes to the tune the fuel curve using the fuel table. Various tables in the XFI software control all the required fuel and timing functions, with a variety of options on how to change the settings and by how much. Before long, our engine was dialed in and running perfectly.