Sylvie Willis
Choosing the right size of the fuel pump is crucial for the optimal performance of your vehicle. The fuel pump supplies fuel to the engine, and the amount of fuel required depends on the horsepower of the engine. As the horsepower increases, the volume of fuel required to support that power also increases. For example, a pump that flows at 50 gallons per hour (gph) should be able to support a 500 hp engine. However, it is important to also consider the fuel pressure required for your engine, as different engines have different fuel pressure requirements. For instance, a carbureted engine typically requires lower psi than a GM LS engine. Additionally, factors such as voltage, fuel type, and the use of a boost can impact the fuel pump's performance. It is recommended to estimate conservatively and choose a pump that is slightly larger than what your system requires, as the excess fuel can simply be returned to the tank.
| Characteristics | Values |
|---|---|
| Fuel flow requirement | Depends on horsepower goal |
| Horsepower | 10 hp per gallon or 2.64 hp per liter |
| Fuel pressure | Carbureted engine: 4-7 psi, GM LS engine: 58 psi |
| Voltage | 13 volts |
| Fuel type | Gasoline |
| Fuel pump manufacturers | Walbro, Tanks Inc, SEP |
| Fuel pump style | In-tank, inline |
| Fuel pump features | Pulse width modulation |
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What You'll Learn
Fuel pump flow requirements vs horsepower
The amount of horsepower an engine has determines how much fuel flow is required to support it. As horsepower increases, so does the volume of fuel required to support that power. A good estimator of volume to power is approximately 10 hp per gallon or 2.64 hp per liter. For instance, if your pump flows at 50 gph, it should be able to support a 500 hp engine (50 x 10 = 500).
Different engines require different fuel pressures. For example, a carbureted engine typically requires between 4 to 7 psi, while a typical GM LS engine runs on about 58 psi. If you are running boost, the pressure required for your engine may increase under load. It is important to know the maximum pressure your engine will require because fuel pressure significantly affects how much flow a pump can produce.
The equation for fuel flow is: fuel flow (gal/hr) = horsepower (hp) / [(fuel density (lb/gal) / bsfc (lb/ hp-hr)]. Or, for gas: gph = hp / 12 at the pressure required.
For example, if you have an engine that requires 60 psi and your fuel pump will be supplied with 13.5 volts, you can use a flow chart to determine that this pump will flow at 63 gph. Using the 10 hp per gallon rule, we can assume that this pump will support up to 630 hp (63 x 10 = 630). If you use the same pump on a carbureted engine, the pressure required for most carburetors is under 10 psi. Assuming 10 psi and 13.5 volts, the chart shows that the pump will flow at 81 gph, supporting 810 horsepower (81 x 10 = 810).
It is always a good idea to estimate conservatively when selecting a pump. Figure your horsepower on the high side so that you have a large enough pump for your system. If your pump is larger than what your system requires, the excess fuel is simply returned to the tank through the fuel return line.
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Estimating fuel needs
Firstly, you need to calculate your brake-specific fuel consumption (BSFC). This is a measure of the amount of fuel needed per horsepower per hour. The BSFC will depend on the type of fuel being used, and it is usually measured in pounds rather than gallons. For example, a gasoline engine typically requires 0.50 lb of fuel per horsepower per hour. You can multiply your horsepower by the BSFC to get the lbs of fuel per horsepower, and then divide that by 6.25 (the conversion rate from lbs to gallons) to get the gallons per horsepower per hour.
Once you know your BSFC, you can determine your horsepower goal. It is recommended to estimate on the higher side. For instance, a near-stock, naturally aspirated truck motor running pump gasoline with stock cylinder heads will have a lower BSFC of around 0.45.
After determining your horsepower goal and BSFC, you can calculate the fuel pump liters per hour (LPH) or gallons per hour (GPH) required for your desired configuration. To do this, multiply your desired power by your BSFC, then divide the result by 1.585. This will give you the amount of fuel flow needed in liters per hour.
Additionally, it is worth noting that most pumps are rated at their "free flow" state, which means they are flowing at 0 psi. Since pump flow decreases as pressure requirements increase, the free flow state is the pump's highest flowing state but also its least useful. To get an accurate assessment of the pump flow at the actual system pressure, you need to determine the psi of your fuel system and then refer to the manufacturer's charts that show flow rate versus pressure.
Finally, it is important to consider the style of pump that will be most beneficial for your application. Inline fuel pumps, for example, can be larger and have a higher rate of flow since they do not need to fit into the fuel tank. They can be paired or tripled together and wired separately to activate at different times depending on fuel requirements. However, they must be mounted close to the fuel tank or cell to avoid "starving" the pump.
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Fuel pump manufacturers' ratings
Various companies produce automotive fuel pumps, and it can be challenging to determine which manufacturer offers the best product for your specific needs. Here is a detailed overview of the top fuel pump manufacturers, focusing on their distinctive strengths, contributions to the industry, and the features they offer:
Bosch
Bosch is one of the oldest companies in the auto parts industry, founded in 1886 by Robert Bosch. Headquartered in Germany, Bosch has established a global presence with branches in many countries. While they have diversified into household goods and the construction industry, automotive parts remain their primary focus. Bosch is renowned for producing premium fuel pumps suitable for various vehicle applications, both light and heavy-duty. They have a stable and wide market and are known for their research expertise, making them a reliable partner for automotive manufacturers worldwide.
Airtex
Airtex, founded in 1935 as Chefford Master, has transformed itself into a major fuel pump manufacturer with branches in Mexico, Spain, Germany, and China. The company stands out for its dedication to quality and innovation, ensuring reliability and outstanding performance across diverse vehicle models. Airtex employs strict testing procedures to guarantee compliance with the highest industry standards, making their fuel pumps versatile and suitable for both everyday vehicles and specialized applications.
Carter
Carter has been a pioneer in the fuel pump industry for over a century, known for its innovative engineering and comprehensive range of fuel delivery solutions. They cater to both the aftermarket and original equipment manufacturer (OEM) sectors, providing a wide array of options for their customers.
GDST
GDST Auto Parts has rapidly gained a reputation for delivering high-quality automotive components at competitive prices. They focus on advanced manufacturing technologies, ensuring their fuel pumps meet strict quality standards. GDST's customer service and flexibility in fulfilling bulk orders make them an attractive option for businesses.
Walbro
While there is limited information available specifically about the manufacturer, Walbro fuel pumps are mentioned in forums, indicating their presence in the market and their use as an alternative to Bosch pumps.
In addition to the above, other notable fuel pump manufacturers include Motor Components, NUKE Performance, Spectra Premium, Snake Eater Performance, and Racing Power Company.
When choosing a fuel pump, it is essential to consider factors such as voltage, wire gauge, and the type of fuel system your vehicle employs. It is also worth noting that certain vehicles, such as nitrous engines or those used for racing, may require a larger fuel pump to accommodate higher horsepower and fuel flow requirements.
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Inline fuel pumps
The size of the fuel pump you need depends on several factors, including the engine's horsepower, fuel density, and the pump's pressure and flow rating.
One rule of thumb is that you need 10 gallons per hour (gph) at working pressure to ensure sufficient fuel supply for 100 horsepower (hp). So, for example, a 550 hp engine would require a 110 gph pump (Free flow) for 55 gph at 6 psi.
Another factor to consider is the type of engine and fuel system. Nitrous engines, for instance, require more fuel, and a power adder such as a turbo or supercharger will also demand more fuel and pressure. If you're looking for a fuel pump for a high-performance racing engine, fuel-injected daily driver, or a classic car with a carburetor, an inline fuel pump could be a good option.
When choosing an inline fuel pump, it's important to consider the pump's specifications, such as flow rate and pressure, to ensure it meets the requirements of your engine and fuel system. Additionally, factors such as voltage, wire gauge, and the use of a return or non-return style regulator can also impact the size and type of fuel pump needed.
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Fuel pump calculators
One key consideration when using fuel pump calculators is that the results are based on estimations and may not be entirely accurate. It is recommended to consult with a tuner or engine builder to confirm the appropriate fuel pump and injector size for your specific use case.
The calculations involved in determining fuel pump requirements can be complex. A basic equation to estimate fuel flow in gallons per hour (gph) is given by: horsepower (hp) / [(fuel density (lb/gal) / bsfc (lb/hp-hr)]. For gasoline, a simplified version of this equation is often used: gph = hp / 12 at the required pressure.
It's important to understand that fuel pump requirements can vary based on the type of engine and its usage. For example, nitrous engines typically require more fuel, and over-sizing the fuel system can be beneficial. Similarly, power adders like turbochargers or superchargers demand more fuel and higher pressure. In EFI applications, pressure can be a critical factor, while carburetors may require a different approach, focusing on the gph rating at the required pressure.
When selecting a fuel pump, it's advisable to consider the voltage at the pump to ensure adequate performance. Additionally, the wire gauge, circuit breakers, and relays should be appropriately sized for the maximum amp draw. A fuel system with a Return Style Regulator or a Non-Return Style Regulator can typically accommodate a larger fuel pump than what is strictly necessary without causing issues.
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Frequently asked questions
The size of the fuel pump depends on your fuel flow requirement, which in turn depends on the horsepower goal. Modern in-tank and inline fuel pumps can meet most high horsepower demands. You can also use a fuel pump calculator to estimate fuel needs based on horsepower, fuel pressure, and fuel type.
Different fuel pump manufacturers rate their fuel pumps in different ways. Some manufacturers rate their fuel pumps at free flow, which is the highest flowing state but also the least useful as no fuel system operates at zero psi. Other manufacturers may rate their fuel pumps at a given psi. For example, Walbro fuel pumps are rated at 40 psi.
As horsepower increases, so does the volume of fuel required to support that power. A good estimator of volume to power is approximately 10 hp per gallon or 2.64 hp per liter. For example, if your pump flows at 50 gph, it should be able to support a 500 hp engine.
It is a good idea to estimate conservatively when selecting a pump. Figure your horsepower on the high side so that you have a large enough pump for your system. If your pump is larger than what your system requires, the excess fuel is simply returned to the tank.
