Sylvie Willis
The amount of fuel that a fuel pump should pump depends on several factors, including the engine's horsepower, fuel pressure, and fuel flow rate. The horsepower of an engine determines the volume of fuel required to support it, with higher horsepower requiring more fuel. Fuel pressure also plays a role, as different engines require different pressures, and fuel flow rate is influenced by factors such as voltage and amp draw. When selecting a fuel pump, it is important to consider the specific requirements of the engine and choose a pump that can provide sufficient fuel flow while also regulating pressure appropriately.
Characteristics and Values of a Fuel Pump
| Characteristics | Values |
|---|---|
| Fuel flow rate | 30 gph/114 lph, 40 gph/155 lph, 50 gph/190 lph, 78 gph, 62 gph, 63 gph, 81 gph, 110 gph, 140 gph, 250 gph, 255 lph, 415 lph, 450 lph, 525 lph |
| Fuel pressure | 4-7 psi, 10 psi, 40 psi, 43 psi, 58 psi, 60 psi, 100 psi, >100 psi |
| Voltage | 13 volts, 13.5 volts |
| Horsepower | 350 hp, 450 hp, 500 hp, 600 hp, 630 hp, 810 hp, 550 hp, 650 hp, 100 hp, 550 hp |
| Engine type | Carbureted engine, gasoline engine, turbocharged engine, EFI engine, V8 engine |
| Fuel pump type | Inline fuel pump, in-tank fuel pump, mechanical fuel pump, return style regulator, non-return style regulator |
| Fuel pump manufacturer | Walbro, SEP |
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What You'll Learn
The horsepower of your engine determines fuel flow requirements
The amount of horsepower an engine has determines how much fuel is required to support it. As horsepower increases, so does the volume of fuel required to support that power. A good rule of thumb is 10 hp per gallon or 2.64 hp per litre. For instance, if your pump flows at 50 gallons per hour (gph), it should be able to support a 500 hp engine.
However, the fuel pressure required for your engine is also important. Different engines require different fuel pressures. For example, a carbureted engine typically requires between 4 to 7 pounds per square inch (psi), whereas 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.
Fuel pump manufacturers rate their pumps in different ways. Some rate their pumps at free flow, but this is problematic as no fuel system operates at zero psi. Other manufacturers rate their pumps at a given psi. For instance, Walbro fuel pumps are rated at 40 psi.
When selecting a fuel pump, it is a good idea to estimate conservatively and figure your horsepower on the high side. This ensures 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.
To calculate the horsepower of your engine, you can use the formula: Given Horsepower x Fuel in lbs/hp = lbs of fuel for given horsepower. You can then convert lbs/hr to gallons per hour (gph) using the conversion rate of 6.25 lbs to 1 gallon of gas.
Another formula used to calculate fuel consumption is Brake-Specific Fuel Consumption (BSFC), which measures the amount of fuel needed per horsepower per hour. BSFC is usually measured with an engine running on a dyno and is typically quoted for wide-open-throttle conditions. It is a useful tool for examining the relationship between fuel flow and horsepower.
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Fuel pump manufacturers rate pumps differently
Fuel pump manufacturers rate their pumps differently, and it is important to understand these differences when selecting a pump. Firstly, most pumps are rated at their "free flow" state, which means they are flowing at 0 psi. This is the pump's highest flowing state, but it is also its least useful, as no fuel system operates at zero psi. Therefore, it is important to consider the pump's flow rate at a given pressure, as the flow rate decreases as pressure increases.
Some manufacturers rate their pumps at a given psi, for example, the Walbro fuel pumps rated at 40 psi. This rating is more accurate than a free-flow rating, but it is only applicable if your engine is running at the same psi and voltage as the rating. For instance, a Walbro 255 lph pump can produce a pressure of over 100 psi, but its rating is based on running at 40 psi and being supplied with 13 volts.
To accurately determine the flow rate of a pump at a specific pressure, you can refer to the fuel pump's curve chart. This chart will show how the flow rate changes with pressure and voltage. For instance, a pump with a free-flow rate of 78 gph may have a flow rate of 62 gph at 60 psi.
When selecting a fuel pump, it is crucial to consider the specific requirements of your engine. Different engines require different fuel pressures, and the pressure can also increase under load. Therefore, you should know the maximum pressure your engine will require and select a pump that can meet those requirements.
Additionally, the horsepower of your engine will determine the required fuel flow rate. As horsepower increases, so does the volume of fuel required. Using the 10 hp per gallon rule, you can estimate the required fuel flow rate. For example, a pump flowing at 50 gph can support a 500 hp engine.
By understanding how manufacturers rate their pumps and considering your engine's specific requirements, you can choose the most suitable fuel pump for your needs.
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Flow rate increases with voltage
The amount of fuel that a fuel pump should pump depends on several factors, including the engine's horsepower, fuel pressure, and voltage.
When selecting a fuel pump, it is important to consider the engine's horsepower requirements. As horsepower increases, the volume of fuel required to support that power also increases. A common rule of thumb is that for every 10 horsepower, you will need approximately 1 gallon of fuel or 2.64 litres per horsepower. For example, if your pump flows at 50 gallons per hour (gph), it should be able to support a 500-horsepower engine (50 x 10 = 500).
However, it's important to note that fuel pressure also plays a significant role in determining the flow rate of a fuel pump. Different engines require different fuel pressures. For instance, a carbureted engine typically operates at a lower pressure of between 4 to 7 pounds per square inch (psi), while a GM LS engine may require around 58 psi. The maximum pressure your engine will need is crucial, as fuel pressure directly impacts the flow rate of the pump.
Now, let's focus on the relationship between voltage and flow rate. Voltage is another critical factor that affects the performance of a fuel pump. In most cases, cars with a standard charging system and proper wiring can supply up to 13.5 volts to the fuel pump. By referring to the fuel pump's curve chart, you can determine the flow rate at a specific voltage and pressure. As the voltage increases, the flow rate also tends to increase. For example, consider a fuel pump with a free-flow rate of 78 gph at a lower voltage. When the voltage is increased to 13.5 volts, and the pressure is set at 60 psi, the flow rate may increase to 63 gph. This increase in flow rate with voltage is illustrated by the green and blue lines on the curve chart.
It is worth mentioning that upgrading to a higher-flow fuel pump may not always translate to improved fuel economy. While a higher-flow pump can provide additional headroom for future modifications, the fuel injectors ultimately control the amount of fuel entering the engine. Therefore, unless you have other performance upgrades, such as a larger turbo or specific fuel pressure requirements, a standard fuel pump is usually sufficient.
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Fuel injectors control how much fuel goes into the engine
The amount of fuel that goes into an engine is determined by the horsepower of the engine. As horsepower increases, so does the volume of fuel required to support the engine's power. This is because the engine requires more fuel to produce more power.
Fuel injectors are responsible for controlling the amount of fuel that goes into the engine. They are mounted in the intake manifold so that they spray fuel directly at the intake valves. The amount of fuel injected is controlled by a flap valve located in the engine's air intake. As the airflow increases, the fuel distributor automatically increases the flow of fuel to the injectors to maintain a balanced fuel-air mixture.
There are two main types of fuel injection systems: continuous injection and intermittent injection. In a continuous injection system, fuel flows at all times from the fuel injectors, but at a variable flow rate. The amount of fuel sprayed is controlled by a mechanical or electrical control unit. The most common automotive continuous injection system is the multi-point Bosch K-Jetronic system, which was introduced in 1974 and used until the mid-1990s.
Intermittent injection systems, on the other hand, can be sequential, batched, simultaneous, or cylinder-individual. In a sequential system, injection is timed to coincide with each cylinder's intake stroke. Batched injection involves injecting fuel to the cylinders in groups without precise synchronization. In a simultaneous system, fuel is injected at the same time to all the cylinders, while a cylinder-individual system allows the engine control unit to adjust the injection for each cylinder individually.
The choice of fuel pump also affects the amount of fuel delivered to the engine. Different fuel pumps have different flow rates, which are measured in gallons per hour (gph) or liters per hour (lph). The flow rate of a fuel pump depends on factors such as pressure and voltage. As pressure increases, the flow rate decreases, and vice versa. Therefore, it is important to consider the engine's fuel pressure requirements when selecting a fuel pump.
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Fuel pump flow charts help determine the right pump
Fuel pump manufacturers will often include charts that show flow rate against pressure. These fuel pump flow charts are essential for determining the right pump for your needs.
Firstly, it's important to determine whether you will run 43 or 58 psi in your fuel system. You can then consult the charts to get an accurate assessment of the pump flow at the actual system pressure you intend to use. For example, a pump may be rated at 415 LPH at 43 psi, but this flow rate will be lower at higher psi.
The amount of horsepower that your engine has will determine how much fuel flow is required to support it. As horsepower increases, so does the volume of fuel required. 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.
Different engines require different fuel pressures. For example, a carbureted engine typically requires between 4 to 7 psi, whereas 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.
Fuel pumps have different flow rates at different voltages. As voltage increases, so does the speed of the fuel pump, which will increase the flow of a pump at any given pressure. Most cars will produce about 13.5 volts when running. As pressure goes up, the flow rate goes down. The best way to find the flow rate at a given pressure is to check a fuel pump’s curve chart.
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Frequently asked questions
The amount of fuel pumped by a fuel pump depends on the horsepower of the engine. 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.
The horsepower of an engine can be determined by finding the flow rating in gph or lph at a given pressure and voltage.
The best type of fuel pump depends on your engine's requirements. There are two main types of fuel pumps: inline and in-tank. There is also a third option: mechanical, which is reserved for very high horsepower.
You should consider your fuel flow requirement. This can be done by calculating your brake-specific fuel consumption (BSFC). You can then use this rate to size your fuel injectors.
