How to Choose an EFI Conversion Kit

First Fuel Injection

Now that you’ve decided that switching to EFI is the best option for you, the hard work begins.

Converting to EFI isn’t as straightforward as buying a machine, unpacking it, and installing it. Furthermore, I’m not aware of any system that is designed to function in all situations. Fortunately, reducing the range of products available to discover which system or systems are most suited to your needs is a rather simple task. This contains all of the information you’ll need to simply select a system for your car, as well as any additional parts you’ll need to ensure a flawless installation and years of dependable operation.


It’s critical to think about parts compatibility, fuel system requirements, ignition system requirements, and electrical system requirements before deciding which system is best for your application. The majority of aftermarket EFI kits are made for normally aspirated engines that produce less than 650 horsepower. How much horsepower the engine can produce is determined on the amount of the injectors included in the kit, the airflow capability of the throttle body itself, the fuel pressure, fuel pump, and other factors. 90 percent of the market is made up of these kits. However, some products, such as those kits that are fully compatible with power adders, are compatible with far higher horsepower, naturally aspirated combinations.

If you’re using or planning to use a power adder (nitrous oxide, superchargers, or turbochargers), look for an EFI system that was built from the bottom up to work with your chosen power adder.

Fuel System

Each of the points below should be taken into account in order to ensure that your fuel system operates efficiently and dependably. The type of fuel you want to use has an impact on the fuel lines, pump, and regulator you use. If you’re currently running E85 in your carbureted setup, for example, you’re already aware that this fuel is caustic and corrosive to typical fuel system components. I recommend determining this early on in the process to help you narrow down your options.

Because E85 has a higher fuel volume demand than standard gasoline, some kits may not be compatible if your E85 combo produces more than 450 horsepower. The gasoline requirements in some situations exceed the capability of the provided fuel injectors. In other circumstances, the components may not be intended to function reliably with E85

The feed line, delivery line, return line, regulator, filters, and other components of a gasoline delivery system should all be chosen to complement one another. Some kits include some of these items, while others don’t. Because fuel system components can be one of the most expensive parts of an EFI conversion, it’s important to know exactly what a system needs before choosing it for your application.

Fuel Supply

An option is to completely replace the tank with one that has been developed expressly for an EFI system. If you choose to go that route, numerous firms sell gasoline tank kits that include a fuel pump, filter, and sending unit built into the tank as well as all the necessary hardware for installation. Removing the stock fuel tank and replacing it with an EFI-specific tank isn’t as costly as you may imagine, and it comes with a number of advantages:

• You begin with a completely clean tank that has no rust or sediment.

• The fuel that the internal fuel pump is submerged in cools it.

• Unlike a stock pickup, the pickup has been positioned so that it will not be exposed during heavy acceleration or cornering.

Remember that fuel injection systems lack a fuel reservoir, similar to the bowls of a carburetor, where gasoline is stored. Apart from the minimal amount of fuel stored in the fuel lines and rails, no fuel is kept elsewhere other than in the fuel tank. If you do a lot of auto crossing, road racing, or high-g cornering, you should definitely consider an EFI-specific gasoline tank, as fuel splash can expose the pickup in a stock tank.

The fuel system should be built to supply your engine with all of the fuel it requires. Choosing the right fuel pump is simple because most manufacturers offer appropriate maximum horsepower ratings. It’s simple to choose the pre-filter, post-filter, and regulator to go with the pump once you’ve decided on the pump because most manufacturers recommend components that is compatible with that pump.

The most challenging element is determining which size and kind of fuel lines to utilize with all of the additional components. The manufacturer of a throttle body EFI system normally specifies a certain diameter of fuel line to supply the throttle body, but not much more. And the responses will differ depending on who you ask. The following has shown to be accurate in my experience:

Throttle Body Fuel Line Size: Follow the throttle body manufacturer’s instructions. This should be agreed upon with the fuel pump’s manufacturer.

Throttle Body to Regulator Fuel Line Size: Use the throttle body’s manufacturer’s recommendations. This should be agreed upon with the regulator’s maker. Returns should be at least -6 lines long. Use the throttle body’s manufacturer’s recommended fuel line size from the regulator to the tank. The fuel line from the throttle body to the regulator should be the same size as this. Returns should be at least -6 lines long.

Vent Line Size: The vent line should be the same size as the return line. The line specifications for a throttle-body EFI system that requires a -6-feed line to the throttle body, for example, are as follows:

The type of line you use is determined by the sort of fuel you use as well as your own preferences. Because it’s economical and simple to install, push-lock lines are arguably the most popular alternative for fuel systems. However, if you choose a push-lock line that does not have a non-collapsible design with a robust core, it cannot be used as a high-volume pump’s intake. In many circumstances, high-volume fuel pumps can create a high vacuum on the input. Any line that isn’t designed to be non-collapsible will collapse, causing a restriction and possibly pump failure.

Many aftermarket EFI systems additionally demand a return connection to the tank, which necessitates the presence of a vent in the tank. Allowing a return line to be installed should not deter you from choosing a system. Although most factory tanks feature a vent, its size may be a stumbling block. The fuel pump must be positioned in the tank with a return-less-style arrangement to prevent it from overheating.

Furthermore, you shouldn’t expect a 40-year-old tank full of sediment and corrosion to give fuel to your brand-new EFI system. Also keep in mind that a tank like this was built for a low-pressure carbureted fuel system, not a high-pressure fuel injected one. If you want to use the stock gasoline tank, you’ll have to remove it to add the return line provisions, so now is a good time to flush it out. You have a few options if you’re using a stock-style tank. You can either flush it and make provisions for a vent and return line, or you can install one of the many in-tank gasoline pump kits that are easily available.

A return-style system also necessitates the employment of a return-style regulator. They are available from a variety of businesses. A return-style regulator differs from a traditional regulator in that it is designed to be installed at the end of the fuel system and serves as the point of origin for the return line.

Ask any engine builder where you should put an external electric fuel pump, and they’ll all tell you to put it underneath the gasoline tank and below the lowest point of the tank. Because electric gasoline pumps are better pushers than pullers, this is the case. Gravity feeds fuel to the pump by placing the pump below the tank’s lowest position, regardless of the tank’s level. The pump being placed below the tank guarantees that the pump never runs out of fuel during heavy acceleration, which is also a good idea. However, in many circumstances, this is just unacceptable because it places the pump well below the vehicle’s rear bumper and in plain sight.

Regardless of whether an external pump is installed forward or rearward of the tank, it must be mounted as low as feasible in relation to the gasoline tank. It goes without saying that you can’t position it in such a way that debris on the road damages it or the gasoline lines. In some circumstances, you can locate the pump along (or even within) the frame rail, which keeps it safe and keeps it below the gasoline tank’s lowest point. You must keep the level of fuel in the tank above the inlet of the pump if you are unable to locate the pump below the lowest position of the fuel tank. Otherwise, you risk harming the pump.

Filters for the fuel system are also crucial: one before the pump and a much finer one before the injectors. Some systems come with one or both filters, while others require you to provide them.

EFI systems function at a substantially higher fuel pressure than carburetors, in case you didn’t know. Fuel pressure in a carbureted system should be between 5 and 7 psi. A higher operational fuel pressure is required for EFI systems. This involves the use of an EFI-style electronic fuel pump, which can be mounted inside or outside the tank. If your car still has the factory fuel line, it may be essential to update it to fulfill the system’s fuel requirements. Some systems are incompatible with hard lines, so keep that in mind.

Throttle Body

High Horsepower

As a result, you’ve got a wicked combo that generates a lot of power. This indicates that a high-flow electric or mechanical fuel pump is also in use. You may need to replace that fuel pump with a high-flow electric fuel pump capable of significantly higher operating pressure as you switch to EFI. Big electric gasoline pumps draw a lot of electricity, so make sure you wire it according to the manufacturer’s recommendations, and make sure your charging system can handle it. If you’re also switching to a return-style system, you’ll have to deal with a new problem: heating the fuel.

The majority of the high-volume electric fuel pumps on the market are designed for short-term use at the drag strip rather than long-term use on the street. When such a gasoline pump is used in a return-style fuel system for a street use, a large amount of fuel is moved to the front of the car, and any fuel that isn’t consumed is returned to the tank. The fuel is heated as it is circulated. Long-term operation of a high-volume pump is not recommended because it can lead to pump failure. It’s a far better idea to control pump speed based on fuel demand, but how? Pulse width modulation is a technique for varying the breadth. That’s how it works.

PWM permits the pump speed to change in response to the engine’s actual fuel demands. In the same manner that the ECU manages the output of a fuel injector, a PWM fuel pump controller manages the pump speed by adjusting the duty cycle.


One of the drawbacks of high-density EFI systems is that they usually require a strong vacuum signal at idle, such as 10 inches or more of manifold volume. Camshaft profile limits are specified by some manufacturers (e.g., duration at .050 inch must be less than 250 degrees). If your camshaft profile deviates from their suggestions, you should call their tech support department for advice before proceeding. If they recommend a different camshaft profile, don’t be surprised.

Ignition System

Some aftermarket EFI systems, as mentioned earlier, also allow you to control the engine timing (engine management). Managing fuel delivery and engine timing concurrently and electronically opens up a lot of tuning possibilities, making it easier to improve drivability and performance. It’s critical to understand the manufacturer’s recommendations for igniting the fire in the cylinders, regardless of whatever approach you use. You can use part or all of your existing ignition components with some kits.

It’s critical to understand the manufacturer’s recommendations for igniting the fire in the cylinders, regardless of whatever approach you use. You can use part or all of your existing ignition components with some kits. Some or all of the components in other kits must be upgraded.

If you choose an engine management system, you must eliminate all external timing influences such as centrifugal advance, vacuum advance, boost retard, nitrous retard, dash-mounted timing controls, and so on. Based on all of these variables, the ECU electronically adjusts the timing. It may be as simple as shutting out your distributor’s centrifugal or vacuum advance. Also, if you’re like most performance enthusiasts and utilize a stand-alone capacitive discharge ignition box for a higher spark, you’ll want to make sure the kit you choose permits you to keep it.

In addition, it might be a good time to think about triggering the ignition system directly, rather than through the ECU. The old way of letting the distributor to manage this is the most popular. However, I’d be remiss if I didn’t remark that now is the time to think about using a crank trigger.

You can avoid any slippage in the timing chain and/or cam gear on the distributor by using a crank trigger. If you had a timing issue with your carbureted combination for whatever reason, you’ll have the same difficulty with the EFI system.

Electrical Systems

The only system in the car that can impact the operation of the others is the electrical system. If you have any electrical issues that you’ve been meaning to take care of, do it before upgrading your EFI.

If you remember nothing else from this, keep in mind that an EFI system is a significant financial investment. If you deprive its components of the current, they need to function properly, you risk causing damage to the components or possibly your engine. At the very least, you’ll have a difficult time getting the system to work effectively, let alone optimally. The most common mistake that enthusiasts make is selecting the incorrect alternator. If you’re going EFI, you’ll probably need to replace your alternator and potentially the wiring. You can easily make this determination while your vehicle is running, and the carburetor is attached. I can’t emphasize how critical this is.

The ECU may demand between 10 and 40 amps of current, depending on the setup you choose. Furthermore, the electric fuel pump can use anywhere from 10 to 30 amps of electricity. On the low end, compared to a carbureted application with a mechanical fuel pump, there is a 20-amp increase in current requirements.

How to Choose an EFI Conversion Kit