Fuelish Tendencies

Proper Fuel System Setup and Components

A fuel system is just that—a system! All the pieces and components must work together.

Fuel⋅ish
A play on words that combines ‘fuel’ and ‘foolish’. Fuel, because this article discusses automotive and marine fuel system design and components. Foolish, because mistakes in fuel system design can result in lost races, personal injury, damaged components, or destroyed engines. The tendencies for this type of problem is more common that many may realize.

The current fuel system trend is to run a pump that provides considerably more volume than should be required to compensate for other deficiencies within the system. Any basic online search will provide hundreds of videos of engine explosions on engine or chassis dynamometers, in addition to those that occur on the race track. Simply purchasing and installing a fuel pump with the greatest output available is not adequate if the rest of the system is poorly designed or sloppily implemented. The same is true when purchasing a fuel pump based upon price, or by what someone believes is enough fuel delivery output for the application. Either deficiency can easily drain the wallet if the engine runs out of fuel and start damaging expensive internal engine components … not to mention lost races!

This article will focus on electric fuel pumps. Mechanical fuel pumps are often not worth the effort, unless mandated by the rules of a specific racing class (as in many circle track applications). It is possible to use the same basic knowledge provided here when determining the proper mechanical fuel pump with regards to requirements and fuel regulator choices.

Some Basic and Fundamental Information:

Fuel pumps are generally rated in gallons per hour (or GPH). Common pump ratings include 70, 110, 140, 250, and 420 GPH. Some fuel pump manufacturers will use a pounds of fuel per hour rating (lbs/hr). Fuel pump manufacturers typically offer pumps of various flow ratings and output specifications. It is a good idea to review all data provided on the pump to make sure the unit purchased meets the demands of the application. One of the highest quality and most powerful fuel pumps available are those from Weldon. Weldon provides highly detailed and accurate data for every fuel pump they manufacture.

Fuel pump designs will vary internally. The most common is a rotary, vane-style design. A vane-style pump can both pull and push the fuel. Meaning, most vane-style pumps can draw fuel from the fuel tank or cell before pushing it toward the engine For this reason, some installers may ignore mounting the pump in the proper location—below the top of the fuel tank. In contrast, Mallory fuel pumps utilize a gerotor design which offers quieter and sometimes more efficient operation than rotary, vane style pumps. In addition, the gerotor pump can only push the fuel, requiring a gravity-feed condition where it is mandatory to mount the pump below the top of the fuel tank.

Installing a fuel filter between the fuel tank and the pump is required for all systems. This mandatory for all fuel pumps, but more critical when using the higher efficiency and tighter clearances of the gerotor pump. The gerotor is less tolerant of impurities and particulates in the fuel that reach the pump. The best practice is to always run a filter before the fuel pump, no matter the pump design! A second, high quality and properly rated fuel filter is also required before the carburetor or fuel injector rail.

A typical gasoline engine uses 0.5 pounds of fuel per hour to make each horsepower. Note: Alcohol and other exotic fuel demand values are not the same as those for gasoline. Gasoline weighs in at approximately 6 pounds per gallon. To calculate fuel consumption, we can begin by using a simple example—a common 400 horsepower engine (or nitrous system). The following formula is used calculate “free flow” fuel requirements:

However, if a pump rated at 33 GPH on a 400 HP engine or a 400 HP nitrous system was installed on this application using the above example, the engine would experience severe fuel starvation and someone’s wallet would cringe in pain as it quickly empties when replacing various parts or an entire engine! Ouch, and why could this occur?

There are several reasons why relying on this calculation will destroy an engine. However, the main reason is related to how fuel pumps are rated. Fuel pumps are typically rated at “zero” pressure (also known as “free flow”). Rating a fuel pump at zero pressure is useless and nothing more than a marketing gimmick, because the pump will never operate at zero pressure when it is supplying fuel to the engine. As fuel pressure increases, the fuel pump slows down and fuel output is reduced. If using a standard “dead-head” type regulator, the pump on a common carbureted application may be forced to produce as little as 25 PSI. At 25 PSI the actual output GPH of the pump is much less than its “free flow” rating.

Choosing the Correct Size Fuel Pump

Many considerations and concerns make choosing the proper fuel pump size somewhat complicated. Use the following information as a fuel pump size “rule of thumb”. Furthermore, ensuring that the fuel system includes an adequate ‘safety cushion’ where its output is slightly more than necessary. Note: This author/engine builder/racer always runs a fuel pump that is just a bit larger than needed, just for insurance.

For Dead-Head type regulators:

Multiply maximum horsepower by 0.23 to calculate minimum pump size in “free flow” GPH.
Example: 400 HP x .23 = 91 GPH “free flow” or lowest possible fuel volume requirement.

For Return-Style regulators:

Multiply maximum horsepower by 0.17 to calculate minimum pump size in “free flow” GPH.
Example: 400 HP x .17 = 68 GPH “free flow” or lowest possible fuel volume requirement.

These minimum pump sizes assume that the fuel system is equipped with fuel lines and fittings of adequate size, and installation performed properly. If the fuel lines are too small (or if using restrictive fittings in the system) a larger pump is often required to satisfy the fuel demand of the engine. The minimum fuel line size (from the pump to the regulator) is dependent upon the horsepower output of the engine (and/or Nitrous system) regardless the size of the pump.

Use these basic figures as a fuel line sizing standard:

Up to 250 HP = 5/16″ or -04 AN
Up to 375 HP = 3/8″ or -06 AN
Up to 700 HP = 1/2″ or -08 AN
Up to 1000 HP = 5/8″ or -10 AN
Up to 1500 HP = 3/4″ or -12 AN

If using a return-style regulator, an adequately sized return line from the regulator back to the tank is also required. The size of the return line is dependent on the size of the pump you are using, regardless of the engine’s horsepower output. The return line must operate at a measured limited (below supply) or preferred ZERO pressure. In most cases, the minimum return line size matches that of the supply line, but a larger return line is often preferred.

Use these ratings to determine return line sizing based upon fuel pump output:

Up to 45 GPH = 5/16″ or -04 AN
Up to 90 GPH = 3/8″ or -06 AN
Up to 250 GPH = 1/2″ or -08 AN
Up to 450 GPH = 5/8″ or -10 AN

Mounting the fuel pump also takes some thought and planning. The fuel pump must be mounted as low as possible and as close to the fuel cell (or tank) as possible. DO NOT mount the pump above the fuel tank. However, the type of fuel pump needs to be taken into account here. Gerotor style pumps provide little to no initial suction, and are push-only style pumps. Mounting a gerotor pump at a location that does not provide gravity-fed fuel delivery will cause the pump to burn up and fail in short order. Vane style pumps do offer a limited amount of suction. However, the more suction, the less efficient the design of the pump. Follow the pump manufacturer’s installation instructions on mounting location, but keep the above facts in mind when planning the most effective and safe mounting location.

Fuel Pump Mounting Angle Customers sometimes ask about the fuel pump mounting angle. They may have an application with limited space or other issues that may make proper mounting difficult. The question typically addresses whether the pump requires upright mounting. To be clear, it depends on the fuel pump design. On some fuel pump designs it matters, and on others it doesn't. In most cases, following the manufacturer's instructions is the best answer. However, if considering an alternative mount angle, it is important to understand potential consequences. If the seals in the pump happen to fail, what happens if the fuel leaks into an electric motor or simply onto the ground? The potential for a vehicle fire, explosion, or environmental problem increases. Cutting corners or ignoring installation instructions can result in hazardous consequences. Just do it right! Follow the manufacturer recommendations.

Mount the fuel pressure regulator as close to the engine as possible. (Note: There are some specific exceptions to this rule. Please review the system designs below.) DO NOT use restrictive fittings, especially sharp 90º or “T” fittings. If the only option is a 90º or “T” fitting, use tube style AN (Army-Navy) fittings from Earl’s, Russell, Goodridge, or other quality brands.

Good and BAD Plumbing Fitting Designs

Of course the fitting at left is what we want to use for optimum flow and minimal restriction. The inherent restriction of the fittings at right can be hazardous to our race engines and affect the consistent ability to win races. The first image is an example of a typical full-flow AN fuel fitting, while the second image show very restrictive brass fittings.

The restrictions caused by improper components or plumbing of a fuel system can cause adverse and costly consequences. It was decades ago when race teams copied technology from the aerospace industry (as they tend to do regularly) in using stainless steel braided fuel lines and AN (Army Navy) fittings, including full-flow screw together hose ends and adapters that drastically reduced common fluid restrictions. Removing fuel flow restrictions and turbulence provided the benefit of using smaller, lighter, and more efficient fuel pumps. Engines were able to make more horsepower throughout the RPM range, were more consistent, and lasted longer. The braided lines resisted wear, heat, and compression, and the hose ends reduced turbulence and restriction while providing added safety, and easier installation and removal. AN hose ends and adapters are manufactured to provide complex bends and connection angles that were previously a plumbing nightmare.

Fuel Pressure Regulators and Benefits of the Return-Style System

One of the biggest restrictions in modern aftermarket fuel systems is the “dead-head’ regulator. Dead-head regulators are popular because installing a return line is not required. However, dead-head regulators are not only more restrictive, they also create several other problems that can be eliminated by using a return-style regulator. Dead-head regulators also have a higher failure rate and shorter life expectancy than return-style regulators.

Weldon, Mallory (now part of MSD), Aeromotive and other fuel component manufacturers offer both dead-head and return-style regulators. Regulator choice depends upon system/application demand and racing class requirements. Dead-head regulators regulate pressure by starting and stopping flow. Return regulators regulate pressure by sending excess fuel back to the fuel tank in a continuous cycle. If confused about the proper regulator choice, think of this simple analogy of a dead-head regulator’s operation:

You may have a childhood memory of running around the house chasing a sibling or a friend. What happened when we chased them into a room and they tried to keep us out by closing the door. However, they did not get the door all the way closed because we were applying pressure against the door? They are pushing, we are pushing while the door is only open a few inches. Suddenly, the person on the other side of the door lets go and moves out of the way. Remember stumbling across the floor trying to regain balance and not destroy furniture or plant our face into the floor? A dead-head regulator is similarly doing the same thing. Fuel is the object pushing, and the regulator is holding the door while periodically jumping out of the way.

Because a dead-head regulator starts and stops flow, fuel pressure between the pump at regulator is higher than the pressure between the regulator and the carburetor. This is different on many fuel injected applications, where the regulator is positioned after the fuel rail so that all of the injectors see maximum pressure and flow. However, if the fuel pressure gets too high, damaging the fuel pump is possible. Therefore, the pressure coming out of the pump is limited in many pump designs by a device built into the pump called a pressure bypass. Low pressure pumps are limited to less than 9 PSI and should not be used with dead-head regulators. High pressure pumps for carbureted applications are limited to a pressure between 10 and 25 PSI.

Not only can the fuel pumps used with dead head regulators fail because of pressure issues, but pumps with dead head regulators also run hotter and do not last as long as the return-style regulators because it is the fuel that cools the pump. The fuel pounding against the dead-head regulator cannot move freely, creating more heat. Fuel pumps working against a dead-head regulator make more noise during operation.

The Mallory 70 and 110 pumps are low pressure pumps that can be used without a regulator for the street or with a dead head regulator for racing. Mallory 140 and 250 series pumps are high pressure and high volume pumps, and must be used with some type of regulator, either dead-head or return-style.

Many fuel pumps utilize an bypass to prevent over-pressurization. It is possible for the bypass in the pump to malfunction. This can cause the pressure to drop or increase to a point that causes the pump motor to fail. Even if the bypass in the pump is working correctly, it is still possible to have a pressure drop with a dead-head regulator, including applications using a high output fuel pump. See the image below:

For example. Using the graphic above, and the engine operating at idle speed, gauge #1 reads 10 PSI and gauge #2 reads 8 PSI. At full throttle, the increase in fuel flow will create a pressure drop between the pump and the regulator. The amount of pressure drop is dependent upon any restriction in the fuel line. A 4 PSI drop is not uncommon. Gauge #1 will now read 6 PSI, and because a dead-head regulator cannot raise the pressure, gauge #2 will also now read 6 PSI. The result is a 2 PSI pressure drop at the carburetor or Nitrous solenoids even though a high output fuel pump may be in use.

NOTE: When using a dead-head regulator, a second gauge should be installed just before the regulator. This allows monitoring of the pressure before the regulator to ensure that it remains above the set pressure.

Many racing specific fuel pumps have the bypass set very high (14-25 PSI) to avoid this problem. However, this creates another problem. The higher bypass pressure makes the pump work harder while also drawing more operating amperage from the vehicle’s electrical system—typically just a high cycle battery or two. In fact, the pump works just as hard at idle as it does at full throttle down the track! This is one of the main causes of early pump failure. To counteract this problem of high amperage draw, some companies manufacture voltage reducers for street cars to slow the pump down and increase the life of the pump. Reducing the voltage supply to the fuel pump can create new problems, because many electric motors are also sensitive to receiving less than required energy.

Why a Return-Style Regulator is Recommended

Why does an engine builder, tuner, fuel pump manufacturer, carburetor builder, or this author recommend or mandate using a return-style fuel pressure regulator for the majority of vehicles? A few easy-to-understand reasons come to mind:

To avoid problematic headaches (such as fuel pump failure just before a final-round elimination, and not having enough time on a hot-lap, or for that matter having a spare pump, to fix the problem in time for the next race. Loss By Default because the dead-head regulator helped shorten the life expectancy of the fuel pump.
The bypass in the pump is plugged or disabled when running a return-style regulator so there is no chance of that component failing.
The pressure just before and after the pump is always the same on a return-style system. Utilizing multiple pressure gauges is not required. Fewer components and issues to monitor.
The return regulator has complete control over the pump pressure and will automatically compensate for pressure drop in the fuel line.

In this example, the system pressure is set at 8 PSI. If a 2 PSI pressure drop occurs between the fuel pump and regulator, a return-style regulator allows the pump to produce 10 PSI. If a 4 PSI drop occurs, the pump is allowed to produce 12 PSI. In either case, the pressure at the regulator will remain at 8 PSI (or maintain the prescribed pressure setting). Pump longevity is extended, since it is required to produce only 10-12 PSI versus 14-25 PSI on a dead-head system. This means that a voltage reducer is not necessary, even on a street-driven application.

Fuel pressure regulators often suffer from a situation called “recovery time”. Recovery time is explained as the amount of time it takes the regulator to react to changes—such as a sudden increase in fuel demand (for example when we smash down the throttle at launch (drag racing application) or activate a Nitrous system). Return regulators react faster, offering less lag or recovery time to maintain pressure for several reasons. Return regulators allow the fuel to flow straight through without making a 90° turn and pounding up against that ‘closed door’ of the dead-head regulator. A return-style regulator doesn’t redirect the fuel around the plunger, offering smoother flow and reduced turbulence. Just before smashing the throttle (or pressing the nitrous button), the fuel in a dead head system is barely moving. In a return system, the fuel is constantly moving from the rear of the car to the front and back again. This means that the fuel maintains a type of momentum, further reducing recovery time. This constant fuel movement assists in cooling the fuel pump, reduces the chance of vapor lock, and benefits fuel atomization once it reaches the engine’s cylinders.

“We never race at any hot or humid tracks in the heat of summer, do we?” {sarcasm}

Dead-head regulators also contribute to another pressure problem known as “creep”, which means the fuel pressure tends to slowly increase when its not actively moving. Return regulators cannot experience a creeping increase in pressure if setup properly and using the properly sized return line for the application.

Fuel Pressure Adjustments

Accurate fuel pressure adjustment on the regulator is only achieved when fuel is flowing through the regulator. Therefore, on dead-head systems the engine must be running to adjust the pressure accurately. The same is true for a Nitrous system. Do any of us really want to “guess” whether the fuel system pressure is set properly the first time the nitrous button is depressed? In a sense, that is what we do. We are making an educated guess, using mathematical calculations and with a small amount of hope, that the systems is configured properly to prevent a catastrophic event. Attempting to adjust the fuel pressure while the nitrous system is active is not recommended. Adjustment of return-style regulators can occur with or without the engine or nitrous system operating. Turn on the pump and set the pressure—simple as that! Of course, fine tuning may be required when performing engine-on testing.

One issue that can make a return-style system operate poorly is too much restriction in the return line. To determine if any restriction exists in the return line, turn the pump on (with the engine or Nitrous off) and back the adjustment screw nearly all the way out. Now check the pressure gauge. Less than 3 PSI should show on the gauge (the lower the pressure the better). If more than 3 PSI exists, efforts must be made to reduce the restriction in the return line. This usually entails free-flow fittings at the least, and in many cases a larger diameter return line. Rule of thumb is that the return line should be at least equal in diameter to the supply line. Note: a pressure gauge could be installed in the return line to monitor return pressure.

Nitrous systems are very sensitive to fuel pressure and volume fluctuations. Serious engine damage can occur when the fuel system on a nitrous application is not 100% perfect. It is highly recommended to run two independent fuel systems when using Nitrous (preferably with return-style pump/regulators). Two small systems with small pumps, fuel lines and regulators are usually cheaper than one large system anyway. if forced to use a single, large system, use a return-style pump (return at the pump back to the tank) with two dead-head regulators installed in parallel, not in series. and NEVER use two regulators series in a system with a return-style regulator! Any fuel system with a return regulator must have only one regulator (per system).

Fuel System Designs

BEST Drag Race System — (return style regulator, plus a dead head regulator … weight savings, and efficiency)

BEST Drag Race Nitrous System — (two independent systems, return regulator at pump, one dead head regulator for solenoids, one for carburetor)

BEST Street/Strip System — (two independent systems if using nitrous; return regulators preferred)

An OK System — (one large system with two dead-head regulators in parallel)

POOR System — (one large system with two regulators in series “not recommended”).

In Closing

A properly designed fuel system offers benefits that help win races, reduce engine damage, and increase vehicle safety. Although safety benefits were not discussed above, be certain that each fuel system component is durable, free from defects, and installed correctly. Mismatched components, poor quality line, hose, or fittings, improper mounting, routing or retention, and other issues can cause costly failures or serious injury.

Return-style regulator systems should be used in all but those applications where class rules prevent it. This is also true for electric versus mechanical style fuel pumps. Electric unless the class mandates something else. Mechanical pumps steal horsepower. Proper sizing of the system (pump volume, line size, etc.) is also extremely important. Do it right the first time to save grief and added expense.

The above graphics only offer a few common fuel system examples. Specific racing systems will vary slightly.

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