Ameer Randolph
The horsepower that an engine has will determine 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 rule of thumb is 1/2 lb of fuel per hp per hour with gasoline. A fuel pump will flow at its highest volume when there is no pressure (free flow). As fuel pressure increases, fuel flow decreases. Every pump has a different flow volume at a given pressure. Therefore, it is important to look at a flow chart of whatever pump you decide to buy.
| Characteristics | Values |
|---|---|
| Horsepower | 400-750 |
| Gallons per Hour (gph) | 100-120 |
| Liters per Hour (lph) | 255 |
| Fuel Pressure | 4-7 psi |
| Fuel Volume | 10 hp per gallon or 2.64 hp per liter |
| Fuel Type | Gasoline |
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What You'll Learn
- A good rule of thumb is 0.5 lb of fuel per hp per hour with gasoline
- Fuel pump flow rate is measured in gallons per hour (gph) or liters per hour (lph)
- Fuel pressure requirements vary by engine type
- Mechanical pumps have trouble sucking fuel from the tank under hard acceleration
- Electric pumps are sometimes preferred for drag racing applications
A good rule of thumb is 0.5 lb of fuel per hp per hour with gasoline
When it comes to determining the amount of fuel required for a certain horsepower, a good rule of thumb is that gasoline engines require 0.5 pounds of fuel per horsepower per hour. This unit of measurement is known as Brake-Specific Fuel Consumption (BSFC), which measures fuel flow relative to horsepower and is expressed in pounds/hour/horsepower.
Using this BSFC value, we can calculate the fuel requirements for various horsepower levels. For example, let's consider a gasoline engine with 650 horsepower. We can multiply the horsepower by the BSFC value of 0.5 to find that it requires 325 pounds of fuel per hour.
Now, since gasoline typically weighs around 6 pounds per gallon, we can further calculate the fuel requirement in gallons per hour (GPH). Dividing 325 pounds by 6 gives us approximately 54.17 gallons of gasoline required per hour to support 650 horsepower.
It is worth noting that these calculations assume peak horsepower conditions, usually near wide-open throttle. Additionally, factors such as load, RPM, drag, sea conditions, and efficiency losses can influence fuel consumption and should be considered when estimating fuel requirements.
In the context of mechanical fuel pumps, it is important to ensure adequate fuel delivery to the engine, especially during hard acceleration. While mechanical pumps may have limitations in drawing fuel from the tank, certain modifications, such as larger lines or additional pumps, can enhance their performance. Some mechanical fuel pumps, such as the Carter 172, have been known to support engines with horsepower in the upper 600s.
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Fuel pump flow rate is measured in gallons per hour (gph) or liters per hour (lph)
The performance of a fuel pump is measured by its flow rate, which refers to the amount of fuel it can supply over time. This flow rate is usually measured in gallons per hour (gph) or litres per hour (lph).
To calculate the minimum flow rate required, you can multiply peak horsepower by BSFC (Brake Specific Fuel Consumption). For example, a naturally aspirated 500-horsepower engine with a BSFC of 0.5 will use 250 lbs. of fuel per hour. Since a gallon of fuel weighs 6 lbs., dividing 250 lbs./hr. by 6 gives us a flow rate of 41.67 gph.
It's important to note that fuel pumps are typically advertised by their free-flow rate, which is the flow rate with no pressure applied. However, as pressure increases, the flow rate decreases. For instance, a pump with a free-flow rate of 78 gph may have a flow rate of 62 gph at 60 psi. Therefore, it's crucial to consider the fuel pressure required for your engine when selecting a fuel pump.
Different engines have different fuel pressure requirements. Carbureted engines typically operate at lower pressures, ranging from 4 to 7 psi, while other engines, such as a GM LS engine, may require higher pressures, such as 58 psi. The voltage supplied to the fuel pump also affects its performance, with higher voltages generally resulting in increased flow rates.
When choosing a fuel pump, it is recommended to estimate conservatively and refer to the flow charts provided by pump manufacturers. By understanding the specific requirements of your engine in terms of both volume and pressure, you can select a fuel pump that ensures optimal performance.
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Fuel pressure requirements vary by engine type
Gasoline engines typically require fuel pressures ranging from 30 to 50 PSI, with high-performance engines needing up to 60 PSI or more. Diesel engines, on the other hand, have specific fuel pressure requirements due to their unique operating principles. They rely on precise fuel injection timing to achieve the desired power output, and high-pressure fuel injection systems contribute to their power and efficiency.
The fuel pressure specifications may also vary among vehicles with the same engine type. For instance, turbocharged engines require higher fuel pressure to accommodate increased air intake and achieve timely combustion. Additionally, the fuel pump pressure can depend on the operating conditions, such as engine idling or wide-open throttle, which impact the effective pressure in the fuel system.
The choice between mechanical and electric fuel pumps also comes into play when considering fuel pressure requirements. Mechanical pumps may struggle to draw fuel under hard acceleration, whereas electric pumps can provide sufficient volume and pressure. The selection of the appropriate pump depends on factors such as engine specifications, performance requirements, and personal preferences.
It is important to note that fuel pressure plays a critical role in achieving optimal combustion and engine performance. Accurate fuel pressure ensures proper atomization, leading to controlled explosions in the combustion chamber, which ultimately drives the vehicle forward. Therefore, understanding the specific fuel pressure requirements for different engine types and vehicles is essential for maintaining engine health and performance.
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Mechanical pumps have trouble sucking fuel from the tank under hard acceleration
Mechanical fuel pumps are typically used in older engines with carburetors. They are designed to siphon fuel from the gas tank and push it towards the carburetor, ensuring a steady supply of fuel to the engine. However, one common issue with mechanical fuel pumps is their struggle to maintain adequate fuel delivery during hard acceleration.
During hard acceleration, the fuel in the tank may slosh away from the pickup point, allowing air to be sucked into the fuel line. This can cause the mechanical pump to lose its prime, resulting in insufficient suction to draw fuel from the tank. Consequently, the engine may experience a lag in performance or even stall. To address this issue, some vehicles employ an electric "pusher" pump mounted near the gas tank, which ensures a continuous supply of fuel to the mechanical pump, preventing it from starving for fuel.
The suction capabilities of mechanical pumps are generally limited, and they rely on head pressure and volume to function effectively. This challenge becomes more pronounced in applications with high horsepower requirements, where the pump needs to deliver a substantial volume of fuel to meet the engine's demands. In such cases, the use of an electric fuel pump or a larger mechanical pump with higher flow capacity may be necessary.
Another factor contributing to the difficulty of mechanical pumps in drawing fuel during hard acceleration is the design of the fuel system. The presence of rust, blockages, or leaks in the fuel tank, lines, or filters can impede the pump's ability to create and maintain a vacuum. Proper maintenance and regular replacement of these components are crucial to ensure optimal performance.
Additionally, the positioning of the fuel filter can impact the performance of mechanical pumps. While some argue for placing the filter before the pump to protect it from rust and debris, others contend that this arrangement can hinder the pump's operation by introducing air into the system. As a result, some recommend placing a strainer before the pump and a metal filter after it to balance the need for filtration and uninterrupted fuel flow.
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Electric pumps are sometimes preferred for drag racing applications
Mechanical fuel pumps have been used since the early days of automobile racing. However, electric pumps are sometimes preferred for drag racing applications due to their specific advantages.
Firstly, electric pumps offer greater fuel flow from a smaller unit, which is essential for high-horsepower engines. The ability to control the speed of electric pumps, such as brushless electric fuel pumps, allows for varying fuel flow to meet the dynamic demands of a race. This is particularly beneficial for drag racing, where the engine demands fluctuate during the race.
Secondly, electric pumps provide convenience and ease of installation. They offer fast start-up, constant fuel volume, and simple installation processes. These features are advantageous for racers who need to quickly prepare their vehicles for competition.
Additionally, electric pumps can deliver sufficient volume for nitrous oxide (NOS) applications, which are sometimes used in drag racing to boost engine power. The ability to provide consistent fuel volume, along with the potential for increased volume, makes electric pumps attractive for racers seeking to maximise their vehicle's performance.
While voltage considerations are important for electric pumps, advancements in electric pump technology have made them a viable option for serious high-horsepower engines. The choice between mechanical and electric pumps ultimately depends on the specific requirements of the drag racing application, with some racers opting for electric pumps to gain the benefits outlined above.
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Frequently asked questions
The hp that a mechanical fuel pump can support depends on the engine and the fuel pressure required. A good rule of thumb is 1/2 lb of fuel per hp per hour with gasoline.
The factory-style '65 pump will be sufficient for a 302 engine.
The Carter mechanical pumps are good for 400-500 hp street cars.
The Barry Grant Super Speed Way pump is excellent for a 600-650 hp engine.
The minimum flow rate can be calculated by multiplying the peak horsepower by BSFC, which will give you the fuel usage in lbs./hr.
