Understanding Carburetor to Electronic Fuel Injection Conversions • Muscle Car DIY (2023)

Let’s get the simple stuff out of the way right up front. The job of either a carburetor or fuel injection, whether it’s mechanical or electrical, is actually simple, and that’s to meter the correct amount of fuel based on the amount of air flowing into the engine. (I address volume versus mass shortly.) I know of many cases in which a correctly tuned carbureted combination made slightly more maximum power than an injected one or vice versa. Obviously maximum power is the goal when racing, and in some applications and combinations, some tuners may choose carburetors over EFI. If you drive your vehicle on the street, EFI offers better overall performance and drivability than carburetors.

Understanding Carburetor to Electronic Fuel Injection Conversions • Muscle Car DIY (1)This Tech Tip is From the Full Book, EFI CONVERSIONS: HOW TO SWAP YOUR CARB FOR ELECTRONIC FUEL INJECTION . For a comprehensive guide on this entire subject you can visit this link:

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Most of us own a modern vehicle with EFI. If you don’t own one, you’ve surely driven one. Forget about horsepower for a second and consider the following attributes of such a vehicle:

  • It starts instantly, no matter the temperature.
  • After it’s started, it keeps running.
  • It idles smoothly before and after reaching operating temperature.
  • It has immediate throttle response with no bogs at the hit of the throttle.
  • It maximizes fuel economy.
  • It requires zero input from the operator.

Come on, let’s be honest: how many of these attributes does your hot rod or classic currently share? With EFI, you can enjoy them all.

Understanding Carburetor to Electronic Fuel Injection Conversions • Muscle Car DIY (2)

Fig. 1.1. This 1,000-cfm throttle body from Holley (PN 112-577) has a 4150-style flange and mounts in place of any 4150-style carburetor. Its CNC billet design maximizes airflow and minimizes air turbulence. A throttle body, such as this one, is an integral part of any multipoint fuel injection (MPFI) system. (Photo Courtesy Holley Performance Products)

Air Quality

Before talking about EFI specifics, it’s important to recognize the role of air quality. As the weather changes, so does the air quality. Here are some factors to consider:

  • Whenbarometric pressure increases, the air contracts and its mass increases.
  • When barometric pressure decreases, the air expands and its mass decreases.
  • Whenair temperature increases, the air expands and its mass decreases.
  • When air temperature decreases, the air contracts and its mass increases.
  • As humidity increases, the additional moisture in the air displaces oxygen.

As air quality improves, it is possible to make additional horsepower with an internal combustion engine of any type. This is exactly why your vehicle runs better on a cool spring night than on a hot summer day.

As youdrive in elevation,barometric pressure decreases. Even though the volume of air flowing into the engine may be the same at a given speed or RPM, its mass is decreased because it contains less oxygen.Any fuel-metering system, be it carbureted or fuel injected, is bound by the variables of air quality and altitude. Depending on where you live, one or both of these variables is constantly changing.

As you can plainly see, a high barometer on a cool evening with low humidity at sea level is the recipe for good air. Many enthusiasts are in tune with this, and as a result, their engines are in tune as well. What if you’re not that guy? Maybe you’d rather drive it and enjoy it than constantly tinker with it? Then EFI is especially for you.

Carburetor Limitations

Most guys who run a carburetor have had it on the car for some time or bought it some time ago. When the carb was installed, they calibrated it or paid a professional to calibrate it for them. Once that was done, they simply left it alone and didn’t tune it for changing conditions. Most also seem somewhat happy with the performance of their combination but they’ve given no thought to the fact that fuel requirements are constantly changing with air quality, altitude, barometric pressure, etc. Even though the same volume of air is flowing into the engine at a given RPM, it may contain more or less oxygen depending on the conditions.

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Fig. 1.2. A handheld vacuum gauge like this one is a great tool to have in your toolbox. It allows you to quickly and accurately set the idle mixture screws on your carburetor the first time around. This gauge also has the ability to measure pressure, which is handy to set the fuel pressure. Such gauges are readily available at any automotive parts reseller.

On the other hand, the diehards take advantage of this and tweak their carburetor(s) often to maximize performance. Remember the jet change in the 1955 Chevy in Two Lane Blacktop on the side of the road? Case in point.

Although I don’t consider myself a carburetor expert, I kept my Olds in tune when it was carbureted and it ran really well that way. It ran so well that numerous friends told me that I was crazy for converting it to EFI. One told me after the conversion, “I don’t know why you’re saving that stuff. In a month it’ll all be for sale.”He was referring tothe pair of carburetors and the old ignition components that I was intending to keep for a rainy day. Boy, was he right; I think I sold that stuff before the month was up.

I learned many tuning tips and tricks for carburetors from studying the manual supplied with the carburetor and going through the motions with a few basic tools at my side. I also have numerous books on tuning carburetors that I refer to often, as well as a few friends I consider experts who are always able to give practical advice that works. This is definitely a topic that you can never know too much about.

Becoming an expert in tuning carburetors is a science indeed. Not only do you need to understand how each of the individual circuits works, you must understand how they work together because the functions of most circuits overlap. The most accomplished carburetor tuners that I know do the same two things every time:

They select the correct size and type of carburetor(s): mechanical or vacuum secondary. This is a function of many variables, including but not limited to displacement, RPM, camshaft profile, cylinder head airflow capability, transmission type, torque converter stall speed. And they tweak each of the circuits independently and then tweak the circuits as a whole for the best compromise of performance at wide-open throttle (WOT) and drivability. Ideally, the transition between the circuits should be seamless.

I just introduced a very important word into the equation. That word is drivability and you hear it often when discussing EFI. Drivability refers to a smoothness of operation when using the throttle (accelerating and decelerating) from idling to WOT to stop, and everything in between.

Compromise is an important part of this equation. Keep in mind that if you spend all Saturday afternoon tuning your carburetor for maximum performance, the tune is going to be slightly off later that night when the temperature drops by 20 degrees and the air is denser as a result. Well, what if you didn’t have to compromise? What if you could tune your combination once and forget it? With EFI, you don’t have to compromise and you truly can tune it just once. This is exactly why the OEMs made the move to EFI. Fortunately, all of what you may know from tuning carburetors is also applicable to fuel injection.

Air/Fuel Ratio

Regardless of whether an engine is carbureted or fuel injected, the ratio of air entering the engine versus the fuel metered is a critical component. Quitesimply,theair/fuel(A/F) ratio of a given engine at a given RPM is stated as pounds of air and fuel. For example, 14:1 means that 1 pound of fuel is metered per 14 pounds of air. A/F ratios are leaner at idle and cruise, and richer when the engine is under load and at WOT.

Carburetors versus EFI

By design, a carburetor meters fuel based on the volume of air flowing into the engine. EFI meters fuel based on the mass of air flowing into the engine. Thus, EFI is able to make changes to the fuel metering in real time based on the quality of the air entering the engine. In addition, EFI does this automatically, without any input from you. Let me elaborate.

To adjust a carburetor, you change or swap out parts or manually modify it. This means swapping jets or metering rods, air bleeds, power valves, accelerator pumps, pump cams, and other parts. Installing the correct parts helps you achieve the desired A/F ratio ata given RPM and load. If you’re using a Holley-style carburetor, you may also make modifications to the metering blocks, such as drilling out the power valve restriction channels, etc.

If you’re serious about this, you’ve got a bevy of such parts on hand as well as a quality wideband A/F meter that you use religiously to evaluate the results of any change. My buddy Bill has three of them (two active at all times) and I’ve always got to have one in my lap, sounding off readings, when we cruise in his Olds. His carburetor is always dialed in and he spends a ton of time tuning it. He never goes out in the car without his handheld weather station and an assortment of jets and air bleeds, and he’s not afraid to make a quickjetor air bleed change in a K-Mart parking lot. By the end of this book, I will have converted Bill’s Olds to EFI.

Fig. 1.3. This Kestrel Pocket Weather Tracker allows you to log temperature, barometric pressure, altitude, relative humidity, heat stress index, dew point, air density, wind speed and gust, etc. A tool like this is indispensable when making changes to a carbureted engine at the drag strip as it provides direction on what changes you should be making.

Fig. 1.4. This is the Target Air/Fuel Ratio table from the tune in my 6-71 blown 1972 Olds Cutlass. There are 256 individual cells in the 16×16 grid. This allows you to achieve much finer tuning for drivability than the most finely tuned carburetor.

Before wideband A/F meters became so affordable and made tuning much easier, owners had to tune the old-school way. They took their cars to the drag strip so they could read the plugs and compare the miles per hour on time slips as they made slow and methodical changes. Holley has excellent video tutorials on how to do this on the street (legally) on their YouTube channel. Either way, you’re making mechanical changes to achieve the desired results.

With EFI, it’s just the opposite. You program the engine control unit (ECU) to achieve the desired results and it electronically and automatically does the work for you. For example, let’s say that your desired A/F ratio at WOT is 12.7:1. With a Holley-style carburetor, you make changes to the power circuit and jetting to obtain this. With EFI, you have a Target A/F Map and you plug in the absolute values you desire based on RPM and manifold absolute pressure(MAP).

(Video) Carburetor to Fuel Injection Conversion Beginning

Simply stated, you must mechanically change or adjust carburetion to achieve the desired results. With EFI, the ECU makes changes electronically, which is based on the desired results plotted in the Target A/F Map.

So, how exactly does EFI do this? It uses feedback from the oxygen sensor in the exhaust, which is typically mounted in the collector of one or both headers. The oxygen sensor provides real-time feedback to the ECU that represents the actual operating A/F ratio of the engine, while the system is in closed-loop mode (see Chapter 3 for more details). Based on this feedback, fuel metering is based on the data that populates the Target A/F Table. For example, let’s say that you want a fuel economy– friendly 14.7:1 A/F ratio while you were idling and cruising but desired that ratio to get progressively richer (to a maximum of 12.5:1) at your maximum engine RPM. Done. How cool is that? And it’s simple too.

If you’re the hands-on type and are familiar with tuning your vehicle in general, you may elect to populate the Target A/F Table yourself. If you’re not so familiar, you may elect to begin with a map that was designed for a similar engine configuration to what you have (more on that soon) and tweak it. Depending on the system you choose and the configuration you have, you may also elect to have this done by a qualified tuner on a chassis dyno as I did with my Olds.

Engine Management

So far, I’ve discussed only fuel metering, mainly because that’s the only way I can draw a direct comparison between carburetors and EFI from a functionality standpoint. Many aftermarket conversion systems available today can also influence the engine timing. Systems that can do both are referred to as having “engine management.” Herein lies the real power of EFI and the OEMs have been using this since the 1980s.

If your engine is carbureted, you manually perform all ignition timing adjustments to obtain the desired results. To maximize fuel economy and achieve the lowest possible exhaust temperatures (thereby lowering engine operating temperature), more advanced timing is required during part throttle than is required during WOT. With a traditional distributor, this can be easily accomplished by using a vacuum advance.

Now we all know that you can only have so much base timing before it can be difficult to start the engine. For street or street/strip vehicles, you can use both centrifugal and vacuum advance to achieve the total timing desired for drivability and fuel economy as well as optimum performance at WOT. During periods of drivability, total timing is a function of base timing, centrifugal advance, and vacuum advance. At WOT, engine vacuum goes to 0 (ideally), the vacuum advance becomes a non-factor, and total timing is then a function of base timing plus centrifugal advance. Although this sounds difficult, it really isn’t. Most manufacturers of quality ignition components provide detailed instructions on how to adjust all of these parameters as well as the rate at which the timing comes in.

Now, the above is in no way intended to begin a debate about what is the best way to time a particular engine for a particular application. Rather, it’s intended to outline all of the possibilities and the understanding required to unlock the potential a certain combination can offer with a carbureted application for both drivability and WOT performance. If you haven’t spent the time to do all of the above with your carbureted vehicle, you’ve left horsepower and fuel economy on the table.

If you install an EFI system that also includes engine management, timing can be electronically and automatically manipulated based on numerous parameters: RPM, MAP, coolant temperature, engine start-up, and detonation (which I cover in Chapter 3).

Before you plug in the numbers, you need a clear understanding of the exact effect that timing has on your combination. Many enthusiasts have realized the tipping point of their combination. Being greedy with timing and advancing the ignition too far can cause engine damage. Don’t be that guy!

By now, it should be clear that tuning your engine for optimum performance is somewhat of an art, especially if you run a carbureted setup. If you have not maximized the A/F ratio and timing, you have work to do to unlock the power and/or fuel economy that your combination may be capable of. The art of tuning for optimum performance is outside of the scope of this book, but I present a few different scenarios for the combinations illustrated in this book.

Keep in mind that no two combinations are the same and when it comes to tuning, the words of my friend and engine builder Frank Beck come to mind, “Give it what it wants.”

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OEM Conversions

Not that long ago, many of my friends were converting their fuel-injected 1986–1988 Mustang GTs from speed density to mass airflow (MAF). In 1989, Ford changed the 5.0L Mustang to a MAF design, which added a MAF sensor (or meter, as it is sometimes referred to), in front of the throttle body directly aft of the air filter. This provided more-precise fuel metering, which improved both fuel economy and horsepower potential.

In addition, the ECU supplied with MAF systems provided a far greater range of tuning and adjustability. This was ideal for anyone running a supercharger, which at that time was very popular for these cars. This conversion was not an inexpensive one and was incredibly laborious as it required a major portion of the vehicle wiring harness to be replaced.

Other popular conversions have involved transplanting Chevrolet LS, Ford Modular, or late-model Chrysler Hemienginesintooldervehicles. All are electronically fuel injected, and each of these conversions offers its own unique set of challenges, especially those systems plucked from donor vehicles equipped with a drive-by-wire interface between the accelerator pedal and throttle.

So, you really have three choices when it comes to an EFI conversion:

  • Source the system, harness, and ECU from a donor vehicle and adapt it to your application.
  • Sourcepartsofthesystemfroma donor vehicle and pair it with an aftermarket ECU and harness.
  • Installacompleteaftermarket EFI conversion system.

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Fig. 1.5. This harness from Painless Performance Products allows you to easily transplant a 2005–2006 LS2 into your project vehicle. The harness includes provisions to also plug in the pedal assembly from the donor vehicle so that the drive-by-wire functionality is retained. (Photo Courtesy Painless Performance)

Although the focus of this book is the third option, let’s talk briefly about the second option: pulling an LS2 out of a wrecked 2006 GTO and installing it in your 1965 GTO, for example. Just a few years ago, this was an incredibly tough proposition because of the drive-by-wire system. But today, thanks to advancements in the aftermarket, this is not so daunting. Companies such as Painless Performance offer plug-and-play wiring harnesses to make such a swap far simpler.

Electronic Fuel Injection Components

Any EFI system, OEM or aftermarket, relies on multiple components to perform the fuel metering. Those components include the following:

  • Engine Control Unit (ECU)
  • FuelInjectors
  • Throttle Body (TB)
  • ThrottlePositionSensor(TPS)
  • Idle Air Control Valve (IAC)
  • MassAirflow(MAF)Sensor, standard for OEM
  • IntakeAirTemperature(IAT) Sensor
  • BarometricPressureSensor
  • Coolant Temperature Sensor (CTS)
  • Oxygen Sensor
  • Manifold Absolute Pressure (MAP) Sensor
  • KnockSensor,standardforOEM, optional on aftermarket systems
  • WiringHarness

Engine Control Unit

This is the heart of any electronic fuel injection system. It takes input from the various sensors so that it meters fuel based on parameters programmed into it. No different than a personal computer, an ECU employs a powerful microprocessor to ensure that fuel metering is immediate, smooth, and responsive. Some ECUs can also perform engine management, in which case they may be referred to as engine control modules (ECMs). In other cases, the ECU can also manage the control of an automatic transmission, such as the Holley Dominator, for example, in which case they can be referred to as a powertrain control module (PCM). For simplicity, in this book, I stick to ECU.

Fuel Injectors

In my opinion, fuel injectors are one of the neatest inventions of modern times, and elemental in increasing performance and fuel economy. Their job is to introduce a finely atomized mist of fuel into the engine based on direction from the ECU.

The ECU uses two methods to manage injector output:

  • By turning individual injectors on or off depending on requirements (see “Aftermarket Systems” on page 14 for more details).
  • By varying the output of each of the injectors depending on requirements; it does this via pulse width modulation (see sidebar “Pulse Width Modulation” on page 13 for more details).

Depending on the system, it may have as few as four injectors, or as many as sixteen. Fuel injectors are rated based on pounds per hour (lbs/hr), or how many pounds of fuel they can flow in one hour.

Throttle Body

The throttle body (TB) is an integral part of any EFI system, and just like the throttle blades of a carburetor, it regulates the air flowing into the engine. TBs can have a single throttle blade, dual throttle blades, or a pair of dual throttle blades.

Throttle Position Sensor

When the throttle is opened, the throttle position sensor (TPS) tells the ECU what percentage the throttle blade is open. The TPS is very accurate and provides real-time feedback of the position of the throttle blade to the ECU.

Mass Airflow Sensor

The job of the MAF sensor is to provide the ECU real-time feedback as to the quality of the air entering the engine. As discussed in sidebar “Speed Density versus Mass Airflow” (on page 10), it measures the mass flow rate of the air entering the engine.

(Video) Classic Car Mods- EFI Conversion, Bad Idea?

Fig. 1.6. This complete MPFI kit from FAST, designed for small-block Chevys, supports engines up to 1,000 hp. Note that it includes an intake manifold complete with injector bungs in the runners, fuel injectors, fuel rails, fittings, a distributor with cam sensor, fuel pump, regulator, fuel filters, and all sensors. A kit like this really does take the guesswork out of the equation. The system includes the following: engine control unit (1), fuel injectors (2), throttle body (3), throttle position sensor (4), idle air control valve (5), intake air temperature sensor (6), coolant temperature sensor (7), oxygen sensor (8), manifold absolute pressure sensor (9), and wiring harness (10). (Photo Courtesy FAST)

Fig. 1.7. This is the Holley HP EFI system on my Olds Cutlass. This kit differs from the FAST kit, as it has the injectors located above the throttle bodies themselves and not in the intake runners. It works well for blown applications as the fuel cools the charge as it passes through the blower. All the components are installed on the engine. The reference numbers correspond to components in the above photo and caption.

Idle Air Control Valve

The idle air control (IAC) valve has a simple job: it allows air to bypass the throttle blade, so the engine can idle when the throttle blade is closed. The IAC valve is actuated electronically by the ECU based on parameters set forth in the tune and can thereby control the idle RPM of the engine regardless of whether the vehicle is idling in neutral or in gear.

Intake Air Temperature Sensor

The intake air temperature (IAT) sensor senses the temperature of the air entering the engine and provides that data to the ECU. In non-boosted applications, it’s often the ambient air temperature. In boosted applications, the ambient air is compressed and thereby heated in the process. Therefore, this sensor is often located aft of the blower or turbo in an effort to provide the most accurate data to the ECU.

Barometric Pressure Sensor

Even though this may not be a separate component, some aftermarket ECUs have an internal barometric pressure (BP) sensor to monitor the barometric pressure.

Coolant Temperature Sensor

The coolant temperature sensor (CTS) is located in a water passage in the intake manifold or cylinder head. Its job is to provide the ECU with the actual operating temperature of the engine. Operating temperature is an important criterion as any ECU with engine management can adjust engine timing, fuel enrichment, and IAC settings based on it.

Oxygen Sensor

The oxygen sensor(s) provides real-time feedback of the actual operating A/Fratiooftheenginetothe ECU. The ECU meters fuel according to this feedback, based of course on the parameters set forth in the Target A/FRatioTable.Theoxygensensor(s) is typically located in the collector(s) of the header(s).

Manifold Absolute Pressure Sensor

The MAP sensor provides real-time feedback of the pressure in the intake manifold to the ECU. This is a bit different from what we’re used to seeing on a vacuum or boost gauge, and it is measured in kilo Pascals (kPa).

For the sake of this discussion, consider that 1 bar (or atmosphere) equals 14.7 psi (at sea level), which equals101.325kPa.

At sea level, air exerts 14.7 psi of force on everything, including an internal combustion engine. A naturally aspirated engine has 14.7 psi of force exerted on it and therefore itrequiresonlya1barMAPsensor. A 2 bar MAP sensor is required for boosted applications not exceeding 14.7 psi of boost, a 3 bar MAP sensor is required for boosted applications not exceeding 29.4 psi of boost, etc.

Knock Sensor

This sensor is designed to detect detonation. As we all know, detonation is the killer of even the best of parts and it is to be prevented at all costs in high-performance engines. Pre-ignition causes detonation and it results in combustion occurring too soon while the piston is on the compression stroke. This causes tremendous force to be exerted on the pistons, rods, crankshaft, etc. The net result is ultimately parts failure. When the knock sensor detects detonation, the ECU can quickly retard timing to eliminate it well before you could detect it by ear and lift off the throttle.

Not all of the applications are knock-sensor friendly, especially those with Roots-blown combinations or those using gear drives. The harmonics of the belt in a toothed pulley or that of the timing gears meshing can trigger a knock sensor, causing an undesired retard in timing.

Wiring Harness

Don’t be intimidated by the wiring harness. Although it may look daunting, most of the connections are plug-and-play between the ECU and the various sensors. Only a handful of hard connections to the vehicle are required.

The key to a properly functioning EFI system is the sum of the parts. Like anything else, some of the sensors, specifically the IAC, MAF, and oxygen sensors,require periodic maintenance. Once you’ve learned your way around the software of an EFI system, it’s easy to pinpoint a potential problem.

Fig. 1.8. This illustrates the relationship between boost and the actual pressure in the cylinder. It’s easy to forget that at one atmosphere (1 bar), 14.7 psi, exists in the cylinder at sea level without any boost.

Fig. 1.9. These are the OEM knock sensors found in the valley of an LS engine from a 2002 Chevrolet Corvette. (Photo Courtesy Keith Aguirre)

(Video) Stacey David's GearZ Converting your Carburetor to Fuel Injection

Fig. 1.10. This diagram of a basic wiring harness is included with some Holley TBI systems. Note that the majority of the harness is pre-terminated with plugs specific to the components they mate with. There are only a handful of connections to make to your vehicle’s wiring. Holley refers to these as “Loose Leads” in this diagram. (Illustration Courtesy Holley Performance Products)

Aftermarket Systems

The main different types of aftermarket systems currently available are: TBI, MPFI/MPI, application-specific, stack, and special-application.

In addition, you can pick and choose components from various manufacturers to assemble an EFI system custom tailored to your specific needs.

Throttle-Body Injection Systems

As the name implies, these systems are built around a throttle body. This category includes many of the systems advertised today as “easy to install” and self-tuning. A TBI system is any system that locates the fuel injectors within the throttle-body (TB) assembly. These are typically built on a 4150-style base, which is identical to that of a Holley-style 4-barrel carburetor. The system shownonmyOlds(Figure1.7)isa TBI system.

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Fig. 1.11. This TBI system offered by FAST is based on a 4150-style mounting flange so it’s compatible with a wide range of applications. The fuel injectors are built into the throttle body, which greatly simplifies the installation. This complete system is in the EZ-EFI series and supports engines up to 650 hp. A dual-throttle-body upgrade is available for engines making 1,200 hp or more. (Photo Courtesy FAST)

The injectors typically are mounted above the throttle blades and can be oriented vertically or horizontally with respect to the blades. On a TBI system for a V-8 engine, it is common to have four injectors: one above each of the primary and secondary throttle blades. Depending on the system, the ECU may only activate the secondary injectors once the TPS reaches a certain percentage. In addition, depending on the system, the injectors may alternate from side to side to keep the mixture evenly distributed in the intake manifold.

Fuel distribution is similar to that of a carbureted engine, so it is entirely possible to have uneven A/F ratios from one cylinder to another, especially in Roots-blown applications. Roots blowers tend to push the fuel forward in the intake manifold under boost.

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Multi-Point Fuel Injection Systems

These systems (MPFI or MPI) have the injectors located in the runners of the intake manifold itself. This offers better control of the fuel distribution. In addition, some systems allow you to adjust each injector individually to maximize the A/F ratio for each cylinder. The FAST system illustrated in Figure 1.6 is an MPFI system. MPFI systems have different ways of managing the firing of the fuel injectors. They can be batch fired or sequentially fired.

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Fig. 1.12. An MPFI system has a great benefit, and that is its low profile. Notice how nicely these fuel rails tuck between the throttle body and valve covers on this 434-ci small-block Chevy. Special attention was paid to overall height, including the selection of this low-profile throttle body, so that this package easily fits under the hood of a classic Corvette. This engine was built and tuned by Beck Racing Engines.

Fig. 1.13. Here, a 434-ci small-block engine is installed in a 1963 split-window Corvette. The project was well planned and engine position was considered so it cleared the hood. The casual observer wouldn’t recognize they were looking at a 600+hp engine with a modern fuel injection setup. Only the fuel rails give that away. (Photo Courtesy JE Pro Streets)

Fig. 1.14. This Edelbrock Pro-Flo 2 EFI system is available for Pontiac 326- to 455-ci V-8s. This complete MPFI system includes a single-plane intake manifold with injectors located in the intake runners, fuel rails, throttle body, Mallory distributor with cam sensor, programmable ECU, and handheld calibration module. Two versions of this kit are offered, depending on maximum horsepower, as well as similar kits for AMC, small- and big-block Chevy, AMC/Jeep, small- and big-block Chrysler, and small- and big-block Ford. (Photo Courtesy Edelbrock)

Fig. 1.15. Most enthusiasts agree that nothing tops the looks of velocity stacks. This 540-ci big-block Chevy is sporting a complete Hilborn EFI system. It has the classic stack look with all of the benefits of modern electronic fuel injection. This engine was built and tuned by Beck Racing Engines.

Fig. 1.16. This 383-ci small-block Chevy is equipped with a Hilborn EFI system with short stacks and air cleaners. Yes, with EFI, you really can have it all. This engine was built and tuned by Beck Racing Engines.

Fig. 1.17. If you’re looking for eye candy, this eight-injector EFI hat from BDS fits the bill. Sitting atop this 572-ci big-block Chevy with a setback 14-71 BDS blower, this combo makes more than 1,580 hp on C16. Not only does it look awesome, it functions exactly like those you see used in the Top Fuel classes. Each of the red throttle blades can support up to 600 hp. This engine was built and tuned by Beck Racing Engines.

Batch Firing: Here,the ECU fires an entire batch of injectors simultaneously. For example, GM engines have an odd batch (cylinders 1, 3, 5, 7)and an even batch(cylinders2,4, 6, 8). AMCs and most Chryslers use this arrangement as well. The ECU fires all of the odd or even batch of injectors based on what cylinder is next in line on the intake stroke.

Sequential Firing: Here, the injectors are individually triggered according to the firing order of the engine and position of the camshaft. This system is more precise because the ECU can fire a specific injector just before the respective intake valve opens. This requires a cam sensor so that the ECU knows the precise location of the camshaft when the engine is running. AH all effect sensor in the distributor easily determines camshaft position, as shown in the distributors in Figure 1.6 and Figure 1.14. MSD, Mallory, Fast, and others also offer a handful of distributors with this sensor built in.

Application-Specific Systems

(Video) 1969 Camaro - Convert from carburetor to electronic fuel injection

Some manufacturers offer complete systems that are designed from the ground up for a specific application. These systems are typically MPFI based and include an intake manifold with fuel injector provisions. The advantage to choosing such a system is that all of the components have been designed to work together.

Just a few years ago, such systems were limited to Chevrolet small- and big-block applications. Now, Edelbrock, Pro-M Racing, and other manufacturers have expanded their offerings to include application-specific kits for AMC, Chrysler, Ford, and Pontiac. Pro-M Racing also offers application-specific kits for Buick, Cadillac, Oldsmobile, and believe it or not, even Studebaker.

Stack Systems

Look no further if you love the look of vintage velocity stacks but don’t want the hassle of tuning a mechanical fuel injection system. Several manufacturers, including Enderle, Kinsler, Inglese, and many others, offer “stack” systems, which give you the great look of velocity stacks with the convenience of modern electronic fuel injection.

These systems typically have one “stack” for each cylinder and are much simpler to tune than the mechanical variety. In addition, they’re totally suited for street use.

Special-Application Systems

When it comes to eye candy, not much tops a functioning injector hat sitting atop an old-school Roots blower. Blower Drive Service (BDS) and Enderle offer such systems. Both provide jaw-dropping looks and the performance of modern electronic fuel injection.

In some cases, an off-the-shelf system may not be compatible with your application. Or maybe you’d like to combine one manufacturer’s throttle body with another’s engine management system and use a specific size and quantity of injectors. It’s not as uncommon as you may think and it’s easier than ever to mix-and-match components from several manufacturers to accomplish this. If you build au nique combination, you should speak directly to the manufacturers of the parts to ensure that they work well with one another.

Option Considerations

If you own a vehicle with a small-block Chevy and you’re doing a basic naturally aspirated conversion, your options are mind boggling. If you own any other vehicle, you also have a lot of options thanks to TBI conversion kits. Regardless of what kind of vehicle you own, here are the things that you need to consider before shopping for a system.

Maximum Horsepower

What’s the peak horsepower of your combination? Once you’ve installed the EFI system, are you considering also maximizing other parts of your combination to increase horsepower? If so, how much maximum horsepower does that yield, ideally?

Power Adders

Do you use nitrous oxide, a supercharger, or turbocharger on your combination presently? If not, is this something that you want to consider down the road? (See Chapter 3 for more details.)


As they always say, the devil is in the details. Sure, there may be a group buy in your favorite forum on the system you’ve had your eye on. But have you considered that you may not be able to use any of your existing fuel system and ignition components? You’re better off asking those questions up front so that you know just how much you’ll outlay for all of the components required for the conversion (see Chapter 2 for more details).


Are you doing the installation or are you having it done by a professional? Even if you undertake the installation yourself, you may have to farm out part of the work; having a vent and return provision added to your stock fuel tank, for example.

Understanding Carburetor to Electronic Fuel Injection Conversions • Muscle Car DIY (21)

Fig. 1.18. This big-block Chevy sports dual throttle bodies from Accufab, 96-pound Siemens fuel injectors, and custom-fabricated intake and fuel rails. Engine management on this direct-injected nitrous application is handled via a Big Stuff 3 controller and harness. Notice the MSD crank trigger to keep timing spot on. This engine was built and tuned by Beck Racing Engines.


Are you doing the tuning yourself or are you farming it out to a professional? If you are doing the tuning, you will certainly benefit from a system with self learning.

Self-Learning Basics

Most aftermarket EFI systems have the ability to self learn. People remark, “I just drove it and it learned my combination.” Is this true? Yes, but how is that possible? The system uses feedback from the oxygen sensor to implement the tune loaded into the ECU. This is referred to as operating the system in closed-loop mode.

The two types of self-learning systems are those with a handheld controller and those without. Both operate in much the same way.

Handheld Controller

Systems that include a handheld controller require you to input some basic data about your combination into the ECU via a series of questions or available choices. After you’ve done so, a base tune is created in the ECU from the data you’ve input. These types of systems are designed to be easily configured and to get the vehicle running smoothly in short order.However,this kind of interface limits your tuning options to those that are only available via the handheld controller.

Laptop Computer

Most more-flexible systems require a laptop computer to talk to the ECU.At a minimum,you load a pre-existing tune that approximates your combination into the ECU via the laptop. You can also build a tune from scratch or modify a preexisting tune to suit your particular combination. Such systems include numerous files in the software, and it’s up to you to choose one that closely approximates your combination. Laptop-based systems offer much greater user control over the tune, which can be a good thing or a bad thing depending on how much you want to be involved.

Either way, once you’ve loaded a tune into the ECU, the ECU implements it. It does so as you idle and drive the vehicle in closed-loop mode. This process begins immediately after you start the vehicle and the system has entered the closed-loop mode (see Chapter 3 for more details). In most cases, simply driving the vehicle in closed-loop mode for 5 to 10 miles gets your tune really close. Hard to believe? You’ll be a believer once you agree to take the plunge.

User Interface

Each aftermarket EFI system has a unique user interface,but it’s simply not possible to illustrate them all. For that reason, I use examples of the user interfaces of the systems installed in Chapter 5 (MSD Atomic EFI Handheld Controller) and Chapter 6 (Holley EFI V2 Software)throughout the book. This allows you to become intimately familiar with two examples rather than trying to cover all the popular user interfaces. The MSD Atomic controller and Holley EFI V2 software are representative of their respective product categories.

Each aftermarket EFI system has a unique user interface,but it’s simply not possible to illustrate them all. For that reason, I use examples of the user interfaces of the systems installed in Chapter 5 (MSD Atomic EFI Handheld Controller) and Chapter 6 (Holley EFI V2 Software)throughout the book. This allows you to become intimately familiar with two examples rather than trying to cover all the popular user interfaces. The MSD Atomic controller and Holley EFI V2 software are representative of their respective product categories.

The user interface is your portal to adjusting the parameters of the system. I strongly encourage you to look closely at it on the manufacturer’s website when considering which system is right for you.

(Video) Is it worth it? Replacing your carburetor with a Holley Sniper EFI | Hagerty DIY

Written by Tony Candela and Posted with Permission of CarTechBooks

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