Throttle body-style fuel injection conversions have been on the market for several years now. In fact, the aftermarket is loaded with many different choices, each with its own highlighted selling points. Despite what the product rep tell you, they are all very similar with some individual peculiarities. Modern manufacturing with CNC machines, digital measuring, computer-simulated testing programs, and other very sophisticated tools have narrowed the playing field from top-of-the-line to budget-level. They are all very good and do a fantastic job improving performance.
Yet, we still hear a lot of chatter and see a lot of confusion from enthusiasts concerning the conversion from carburetor to fuel injection fuel systems. With many of these EFI conversions celebrating a decade or more in production, it surprises us there are still questions about the choices and installation. A deeper look revealed much of the frustration and confusion was not from the EFI systems themselves, but rather, from the actual fuel delivery system. We caught up with a trusted resource at Tanks, Inc. to look at the other end of the EFI fuel delivery system and clear up some confusion.
Look At The Whole Picture
Every time we’ve asked Justin Somerville of Tanks Inc. a fuel question, he reminds us to look at the whole picture. For that reason, we’re going to start at the beginning with all the generally accepted facts. EFI conversions are popular because they optimize combustion and fuel usage. EFI systems use pressure to introduce fuel into the engine. Carburetors rely on vacuum to get atomized fuel into the engine’s combustion chamber. This gives the EFI system the ability to offer immediate fuel delivery on-demand. For enthusiasts, this means a better throttle response.
EFI systems require constant and stable fuel pressure to operate correctly. This is where some enthusiasts get into trouble when converting to an EFI system. There are various ways to get fuel to the system, with some being better than others, depending on the application. Anytime the system sucks air or experiences a fuel pressure drop, there will be an immediate drivability issue.
We’ve discussed selecting the proper fuel tank and how to plumb the fuel system in past articles. This time we want to focus on selecting the proper fuel pump for an EFI system. Somerville says there are three major factors at play that enthusiasts must consider when designing an EFI fuel system and selecting a fuel pump: horsepower, fuel pressure, and voltage.
Horsepower, Fuel Pressure, And Voltage
Horsepower: This is simply the amount of power your engine is expected to make. Tanks Inc. provides a rough estimator of volume to power is about 10 hp per gallon of fuel. Somerville also reminds us to actually know the gallons per hour a pump delivers, and you must also consider the fuel pressure required for your engine.
Fuel Pressure: We already know a carbureted engine requires less fuel pressure than an EFI system. One thing you might not know is, if you have a power adder, the pressure required for your engine may need to increase under load. It’s important to know the max fuel pressure your engine will need. Fuel pressure requirements have a huge effect on how much flow a fuel pump can produce.
A fuel pump will flow at its highest volume when there is no pressure. As fuel pressure increases, flow decreases. Every EFI fuel pump has a different flow volume at a given pressure. “This is why it is important to look at a flow chart of whatever pump you decide to buy,” says Somerville. The important point is to match the pump’s capacity to the individual application by looking at the manufacturer’s flow chart rating to make sure that you are getting a pump that has the capacity you need. You can view flow charts of the Walbro fuel pumps Tanks Inc. sells by clicking here.
Voltage: Fuel pumps have different flow rates at different voltages. As voltage increases, so does the flow rate of the fuel pump. This is why it is good practice to know a pump’s rating at a given voltage. Most cars will produce about 13.5 volts when running. If you are unsure or you simply want to plan conservatively, look at the flow ratings of a given pump when at 12 volts.
One of the most overlooked items when switching to a fuel injection system is the existing electrical system of the vehicle. When you add more electrical items, the vehicle will probably require some improvement of power distribution, electrical grounds, or perhaps even a higher amperage alternator. If you do upgrade your amp output, make sure the wiring in your car is sufficient. If you have followed our previous articles on EFI conversions or electrical system upgrades, chances are you have already pre-planned for this. So, we’re not going to get into the individual electrical requirements in this article.
The type of fuel you put into your engine also matters. For most pumps and fuel system components, gasoline is the baseline. However, even with the baseline fuel, there are additional considerations. One is brake-specific fuel consumption (BSFC), which is the measure of the fuel efficiency of an engine that burns fuel. Here are the basic guidelines for gasoline:
- Naturally aspirated engines are typically most efficient with a BSFC from 0.4 to 0.5 lbs/hp/hr.
- Nitrous combinations use more fuel and often develop a BSFC from 0.5 to 0.6 lbs/hp/hr.
- Forced induction engines experience a BSFC in ranges from 0.6 to 0.75 lbs/hp/hr.
Engines using Ethanol will likely use 30- to 35-percent more fuel than gasoline-burning engines. Here are the basic guidelines for Ethanol use:
- Naturally aspirated engines are typically most efficient with a BSFC from 0.6 to 0.7 lbs/hp/hr.
- Nitrous combinations use more fuel and often develop a BSFC from 0.75 to 0.8 lbs/hp/hr.
- Forced induction engines experience a BSFC in ranges from 0.85 to 0.95 lbs/hp/hr.
Engines using Methanol will likely use 100- to 200-percent more fuel consumption than gasoline-burning engines. Here are the basic guidelines for Methanol use:
- Naturally aspirated engines are typically most efficient with a BSFC from 0.9 to 1.1 lbs/hp/hr.
- Nitrous combinations use more fuel and often develop a BSFC from 1.2 to 1.3 lbs/hp/hr.
- Forced induction engines experience a BSFC in ranges from 1.8 to 2.0 lbs/hp/hr.
Another topic that is often asked concerns fuel pressure regulators. Basically, there are two types of pressure regulators for most street vehicles today. There is a deadhead regulator which does not require a return line back to the tank, and a return regulator which obviously does. The deadhead regulator operates normally open with fuel flowing through unrestricted once the pressure reaches the preset limit. These are strictly used on carbureted applications and it is highly unlikely you will see this type of regulator used with an EFI system.
The deadhead system will force an additional load on the fuel pump as it operates at or near full capacity, forcing pressure against the regulator. Some pressure-limited-style pumps have an internal bypass that allows flow from the outlet port to return back through the pump into the inlet port. Although some pressure is relieved via the return, there is still pressure against the regulator. For a daily driver that operates at part throttle most of the time, the additional load on the fuel pump can reduce its lifespan. At low-throttle applications like heavy traffic situations, the fuel can get heated by the pump working against the head pressure. In hot weather, this can cause a vapor lock issue. In any case, these pumps are not intended for use in high-pressure EFI systems.
If you are plumbing a fuel system for an engine using EFI or an EFI conversion, a pressure regulator is needed and needs to be accurately set to the desired fuel pressure. Return-style regulators are normally closed until the pressure limit is reached, then a bypass is opened to return excess fuel back to the tank. This bypass reduces the fuel load on the pump, extending the pump’s life and reducing fuel temperature. Many EFI conversion kits have a return provision built into the system. Most EFI regulators are adjustable from 30 psi to as high as 70 psi. This means enthusiasts that need 45 psi at the fuel rail will be able to use the same pump and regulator combination as those who want 60 psi. The important part is to ensure the pump provides the necessary flow at the pressure required.
A Tale Of Two Types
The question of whether an external fuel pump or in-tank fuel pump is better eventually gets asked. We don’t want to get too much more into this aspect of the issue at this point, but here’s what we can tell you: EFI conversions are simplified with in-tank pumps. Tanks that are internally baffled with a reservoir tray ensure the fuel pump doesn’t run dry under spirited driving. The fuel pumps run cooler and last longer when submerged in fuel. Plus, they run quieter, are a lot more efficient, and there is a lot less clutter under the car with an in-tank fuel pump.
According to Somerville, “Our in-tank pumps do use an external regulator, that is unless you are running a Pulse Width Modulated fuel pump (PWM).” When converting a classic car to run with EFI, having a PWM is not an issue so we will not cover that in this article. Now that the air is cleared about pump selection, to find out what EFI fuel pumps and tanks are available from Tanks Inc, visit them online at www.tanksinc.com.