Sylvie Willis
Pro stock cars are a class of drag racing featuring factory hot rods. They are often described as all motor because they do not use forced induction or enhancements like nitrous oxide. The National Hot Rod Association (NHRA) pro stock class emerged in 1970 with a liberal set of rules and no handicaps. Over the years, the NHRA has made several changes to the rules, including implementing a minimum weight and maximum engine displacement. The NHRA also mandates the use of electronically controlled throttle body fuel injection systems and spec fuel for all cars. Pro stock cars are highly modified and can make in excess of 1,300 horsepower, with some engines exceeding 800 cubic inches in displacement. The fuel used in pro stock cars is typically high-octane racing gasoline, which is designed to deliver consistent and reproducible quality, allowing precise engine tuning for maximum performance.
| Characteristics | Values |
|---|---|
| Fuel Type | Racing fuel (octane rating: 118) |
| Fuel Composition | High-quality stocks, additives, antioxidants, corrosion inhibitors |
| Fuel Properties | Ultra-high octane, high-quality leaded fuel, high resistance to detonation, low vapor pressure, clean-burning |
| Fuel Flow Rate | 7.5 US gallons per minute (0.5 L/s) |
| Engine Type | Single-camshaft, 90-degree V8 |
| Engine Displacement | Maximum of 500 cubic inches (8.2 L) |
| Engine Power | Up to 1,500 hp |
| Engine Modifications | No forced induction, head modifications allowed |
| Weight | Minimum of 2,350 pounds (1,066 kg) |
| Production Year | Within the last five model years |
| Fuel Injection | Electronically controlled throttle body fuel injection |
| RPM Limit | 10,500 RPM |
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Racing fuel
NHRA pro stock engines are typically restricted to a maximum of 500 cubic inches (8.2 litres) and have specific requirements for the fuel injection systems. In 2016, the NHRA implemented a major overhaul, requiring cars to use electronically controlled throttle body fuel injection systems with an electronic control unit (ECU). This replaced the previous use of hood scoops and double four-barrel carburetors. The NHRA also mandates the use of a specific Sunoco racing fuel, which may be unleaded or may contain alcohol, similar to other classes of motorsport.
The racing fuel used in NHRA pro stock cars has a high octane rating, typically around 118. This high-performance fuel allows the engines to operate at extremely high compression ratios, resulting in increased power output. The fuel also needs to flow at a specific rate, with NHRA regulations requiring a flow rate of 7.5 US gallons per minute (0.5 litres per second).
Other racing organizations have different rules and regulations regarding fuel. For example, the Australian National Drag Racing Association and IHRA have a maximum engine displacement limit of 400 cubic inches (6.6 litres) and may use either four-barrel carburetors or throttle body electronic fuel injection. Additionally, some organizations, such as IndyCar, use pure methanol as their racing fuel, while Top Fuel dragsters and funny cars burn nitromethane.
The choice of racing fuel is a critical aspect of pro stock car racing and can significantly impact the performance and power output of the vehicles. Teams and organizations must carefully consider the specifications and regulations to ensure they are using the appropriate fuel for their specific class and engine setup.
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Fuel injection
In 2016, the NHRA implemented a significant change to the engine formula, replacing hood scoops and double four-barrel carburetors with electronic fuel injection (EFI). This update aimed to align with modern automotive trends, as all automobiles produced for sale in North America had already been using EFI for over two decades. The NHRA formula now mandates the use of electronically controlled throttle body fuel injection systems, supervised by an electronic control unit (ECU) with a 10,500 RPM limit.
The introduction of EFI in NHRA pro stock cars sparked debates within the racing community. Some argued that the "'stock' portion of 'pro stock'" was becoming less accurate, as the vehicles increasingly incorporated custom parts and deviated from their factory origins. Additionally, concerns were raised about the potential for unfair advantages with the adoption of EFI, as the sophisticated microprocessors used in these systems could potentially be utilized for autonomous driving.
Despite the controversies, EFI offers several advantages. It provides a broader powerband and superior cylinder-to-cylinder fuel distribution compared to carburetors. EFI also excels at higher RPMs, typically performing well above 2,000 RPM. Furthermore, EFI systems are generally easier to tune and maintain than carburetors, contributing to their popularity in various racing classes.
While EFI has become prevalent in pro stock racing, some organizations allow racers to choose between EFI and carburetors. For example, the International Hot Rod Association (IHRA) Pro Stock class legalized EFI in 2001, but racers were given the option to continue using carburetors if they preferred. This flexibility acknowledges the ongoing evolution of racing technology and strives to balance performance enhancements with simplicity and affordability for racers.
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Fuel specifications
Pro stock cars are a class of drag racing featuring "factory hot rods". The class is often described as "all motor" because the cars do not use any form of forced induction, such as turbocharging or supercharging, or other enhancements like nitrous oxide. The National Hot Rod Association (NHRA) pro stock class emerged in 1970 with a more liberal set of rules and an absence of handicaps compared to the production-based super stock.
The NHRA mandates a specification racing fuel for pro stock cars. The fuel must be a high-quality, leaded gasoline with an octane rating of 118 and a Motor Octane Number (MON) of 114. It is designed exclusively for racing applications at sanctioned racing events and is suitable for large-bore racing engines and high-RPM four-stroke cycle motorcycle racing engines. The composition of this fuel is carefully controlled to deliver consistent, reproducible quality, allowing precise engine tuning for maximum performance on the track. It burns cleanly, leaving little to no deposits, which allows for maximum engine power. The high-quality stocks used in this fuel make it very stable and resistant to gum formation, assuring cleaner carburetors, intake manifolds, and valves. A detergent additive further helps to keep carburetors clean, while antioxidants and corrosion inhibitors promote stability and longer shelf life. This fuel does not contain any alcohols or oxygenates.
The NHRA also requires that pro stock cars use electronically controlled throttle body fuel injection systems, with an electronic control unit (ECU) implemented on the EFI systems, including a 10,500 RPM limit (although modern engines are approaching 12,000 RPM). The switch from carburetor to EFI systems was made to reflect modern automotive trends, as all automobiles being produced for sale in North America have used electronic fuel injection for over 20 years. Additionally, EFI systems can reduce costs, increase engine power, and improve driver visibility by reducing the size of the air scoop.
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Fuel combustion
Pro stock cars emerged from the production-based super stock in 1970. The National Hot Rod Association (NHRA) pro stock class has specific rules regarding engines and fuel systems. NHRA pro stock engines are restricted to a maximum 500 cu in (8.2 L) single-camshaft, 90-degree V8. The NHRA formula requires cars to use electronically controlled throttle body fuel injection systems, with an electronic control unit (ECU) implementing an RPM limit of 10,500.
Internal combustion engines, such as those in pro stock cars, typically use a four-stroke cycle. In this cycle, the piston moves within the cylinder to draw in fresh air, compress it, ignite the fuel mixture, and then expel the combustion gases. This process repeats with each stroke of the piston, generating power for the vehicle.
The combustion process in these engines is carefully controlled to maximize performance and minimize emissions. However, even with these controls in place, the combustion of fossil fuels can produce gaseous pollutants, such as nitrogen oxides and carbon monoxide. These emissions can have negative impacts on the environment and human health, leading to respiratory issues and even cancer.
To address these concerns, organizations like the NHRA may mandate the use of specific fuels, such as racing fuel with a high octane rating or ethanol blends. These fuels are designed to reduce the environmental impact of racing and are often tested and certified by chemical analysis. Additionally, modern automotive trends, such as the use of electronic fuel injection, reflect an effort to improve fuel combustion efficiency and performance while adhering to environmental standards.
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Fuel types
The fuel used in pro stock cars depends on the racing organisation and class of racing. The National Hot Rod Association (NHRA) pro stock cars use fuel-injected, naturally aspirated 500 cubic-inch engines running on an approved racing gasoline with an octane rating of 118. The NHRA mandates the use of a specification Sunoco racing fuel, but it is unknown whether this will be unleaded racing fuel or if it will allow alcohol in the official NHRA fuel.
The NHRA formula requires cars to use electronically controlled throttle body fuel injection systems, with an electronic control unit (ECU) implementing on the EFI systems, including a 10,500 RPM limit. The engines in these cars generally produce around 2.5 hp/in3 (114 kW/L) and make upwards of 1,500 hp.
The Australian National Drag Racing Association and IHRA have a 400 cu in (6.6 L) maximum displacement engine limit. Engines may either be four-barrel carburetors or throttle body electronic fuel injection and must be a naturally aspirated intake system.
Indy cars burn pure methanol, while Top Fuel dragsters and funny cars burn nitromethane. Methanol can run at extremely high compression ratios, meaning more power, and has the added safety benefit of being able to be extinguished with water. Nitromethane contains a great deal of energy per unit volume (more than twice that of gasoline) and is basically a liquid explosive.
Some pro stock fans and drivers lament the loss of excitement in the sport, with one fan stating that they "still maintain that national event fans come to see 3-second, 330mph loud ass nitro action and just about everything else is filler for them".
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Frequently asked questions
Pro Stock cars use electronically controlled throttle body fuel injection systems. The fuel must be a specification fuel, such as Sunoco SR18 or Sunoco racing fuel.
Specification fuel is of a carefully controlled composition, allowing for precise engine tuning and maximum performance. It is also more stable and resistant to gum formation, assuring cleaner carburetors, intake manifolds, and valves.
Pro Stock cars use racing fuel with an octane rating of 118.
High octane fuel can handle high compression well, allowing for more power.
No, different racing cars use different fuels. For example, Indy cars use methanol, while Top Fuel dragsters use nitromethane.
