By now the benefits of converting a carbureted vehicle to electronic fuel injection are well known in hot rodding circles – easier cold starts, better throttle response, and the ability for the system to self-adjust to changes in temperature, altitude, and other real-time factors are just a few them. But while making the switch from carburation to fuel injection is easier than it’s ever been before, it’s still a bit more involved than simply removing a carburetor and bolting up an EFI system in its place. Beyond getting everything wired up and connected, there are fundamental differences in the way that carbureted and fuel injected systems operate, and those differences require supporting fuel system components that are also designed for the task.

“With a carbureted system, you have atmospherically vented fuel bowls,” explains Holley Performance EFI Product Manager Harrison Alford. “So the fuel that’s being delivered under pressure to the carburetor basically just needs to keep the fuel bowls filled.

But with fuel injection, the system runs at a higher pressure to ensure that the fuel being delivered is atomized properly as it is sprayed out of the injectors. If you were to drop the pressure in a fuel injection system down much lower than the injectors require, for example 20 psi instead of a common 43, instead of the fuel coming out as a finely atomized spray the fuel would come out in larger droplets and there won’t be as complete of a burn in the combustion process. And that would result in lower efficiency and reduced performance.”

While carbureted fuel systems require fuel pressures of around 6 to 7 psi in most cases, fuel injected systems typically operate at between 43 and 60 psi – or even higher in some applications. And beyond these elevated pressure requirements, the fuel system’s flow rate must also be dialed in for a given powerplant’s fueling requirements. Here we’ll take a closer look at the components you’ll need to consider when making the switch from carburation to fuel injection.

The Right Parts For The Job

It’s important to note that pressure and flow rate are two wholly separate concepts in the realm of fuel systems, and both need to be dialed in appropriately in order for an EFI system to perform at its best.

“In this context, flow is essentially the volume of fuel that’s being moved through the fuel system over a given amount of time,” says Alford. “In most cases, with fuel pump flow rate specifications you’re going to see either ‘gallons per hour’ (GPH) or ‘liters per hour’ (LPH).

Pressure, meanwhile, is the force that’s acting on that flow. And since it’s acting against that flow, it can be considered a resistance. What that means is as you starting increasing the pressure that the system is operating on, your flow decreases. Many fuel pumps on the market – including ours – actually have charts online and included in the documentation which show you the flow curve of the pump, and that’s typically expressed as flow versus pressure.” There are different types of fuel pump configurations to chose from, each with its own benefits (typical inline fuel pump system shown above).

With the significant increase in fuel pressure that EFI requires, it’s important to ensure that other elements beyond the fuel pump are also up to snuff.

Fuel Lines: Handling EFI-Spec Pressures

“The lines need to be able to hold the pressure as well,” Alford notes. “The rubber hoses that someone would pick up at a local auto parts store might work for a simple carbureted application, but the maximum operating pressure of these hoses are typically in the realm of 30-50 psi and not recommended for fuel injection, whereas the lines that are rated for fuel injection can often handle in excess of 150 psi.”

Many of the Earl’s fuel lines that Holley Performance recommends for EFI applications are rated for 225 psi or higher. Metal lines can also be used as long as they’re rated for high pressure. “Of course you can also use some form of AN line. Usually these are high pressure-rated rubber or PTFE (Teflon™) lines with a stainless or nylon outer braiding,” he points out. “PTFE lines can usually handle much higher pressures, so you’ll typically see those utilized for other types of systems like nitrous or, if it’s DOT-approved, brake systems. PTFE-lined hoses are also required if you’re going to be using fuels other than gasoline, like E85 or methanol. Some hoses with AN fittings might work with E85, but they’re unlikely to last as long as a PTFE hose would. If you try to use regular, run-of-the-mill rubber hoses – or AN hoses that use a standard rubber inner liner – with E85, for example, it might work for a brief time, but that material is going to get eaten up very quickly. And that can cause the deteriorated material to clog up fuel filters and injectors.”

Shop Earl's Performance Plumbing fuel system components here.

Regulators: And The Carb Vs. EFI Pressure Game

Regulator: When you’re converting from carburation to fuel injection, you also need to ensure that you’re using an appropriate regulator for the setup. “You’re going to need to use a bypass (return-style) regulator here,” Alford tells us. “With a high-pressure, EFI-style fuel pump, you have to have some kind of bypass because the vast majority of these pumps do not have an internal bypass, whereas low-pressure carburetor fuel pumps usually do.”

The regulator also needs to ideally be matched to the fuel pump you’re using. “You’ll notice that with a lot of our fuel pumps we have regulators that we recommend pairing with them. Our fuel system selection chart is also a good reference to use for this. You need to consider the threading of the regulator ports as well. You may see NPT threads used or AN-ORB threads, which can make things easier if you’re already planning to use AN fittings.”

Another thing you’ll typically see on EFI regulators is the vacuum reference port / boost reference port on the top hat of the regulator. If the injectors are after the throttle blade(s), a vacuum hose from the intake plenum is usually connected there.

“Under vacuum conditions, this lowers the fuel pressure, and if it’s a forced induction application, once you get into boost, it actually increases the fuel pressure,” Alford says. “If the fuel injectors are before the throttle blades, as is the case with a Sniper EFI throttle bodies or Terminator X Stealth throttle bodies, the fuel is actually injected above the throttle blades, so you don’t need to use that vacuum reference line if it’s a naturally aspirated application.”

Shop Holley fuel pressure regulators and associated fittings here.

Fuel Filters: Microns Matter

The filtration requirements of an EFI system also slightly differ from a carbureted application. When it comes to pre-pump filters, things stay mostly the same – if using an inline pump a filter with an 80 to 100 micron rating is recommended, if using an in-tank fuel pump the included sock or a Hydramat can be used.

But when it comes to the post-pump filter, a carbureted application typically utilizes a design with a 30-to-40-micron rating, whereas a fuel injected system should be outfitted with a filtration rating of 10 microns or finer.

Shop Holley's wide variety of Hydramat products here.

Shop Holley inline fuel filters here.

Fuel Pumps: Primetime Players

Fuel pump: As mentioned earlier, EFI systems require fuel pumps significantly higher fuel pressure ratings than those used with carbureted applications, so if you’re making the switch from carb to EFI, a new pump will likely be near the top of your shopping list. In addition to the pressure rating, the flow rate also needs to be taken into account.

“When it comes to determining the flow rate you need, it really comes down to how much horsepower the engine is making and the type of fuel you’re going to be using,” says Alford. “For example, if you have a naturally aspirated small-block that makes about 500 horsepower at the crank running on pump gas, the flow requirements for an EFI application are going to be similar to the requirements of a carbureted application, but those flow requirements need to be met at those higher pressures that the EFI system operates at. You also need to keep in mind that if you’re using a different type of fuel, like E85 or methanol, those fuels will require a significantly higher flow rate. There are common flow rate calculators available online that can help you determine what you need.”

Beyond the flow and pressure ratings, there are also some other attributes that need to be considered when selecting an EFI pump for your build – like whether you’re going to use an externally-mounted pump or an in-tank pump. It’s also important to note that some newer pump designs are equipped with brushless motors, which will be quieter and more efficient than those with conventional brushed motors but often require special controllers.

Stay tuned for Part 2 where we will explore what it takes to up your fuel game on an already EFI engine.