Nitrous
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This page discusses the use of nitrous oxide in a racing context. For other uses, see Nitrous oxide.
Nitrous is a slang term for nitrous oxide (N2O), commonly used by drag racing classes like Pro Street, Top Sportsman, and Pro Mod. Nitrous oxide is an oxidizing agent used to increase an engine's power output by allowing for faster burning of a fuel (usually gasoline). Nitrous can be used with alcohol in the mud racing categories.
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Overview
Nitrous oxide is not a fuel, it is an oxidizer. It carries more oxygen to the engine, allowing for faster burning of the fuel and generating more power. At high temperatures, such as those found inside a firing cylinder, nitrous oxide breaks down into nitrogen and oxygen gas. This raises the partial pressure of oxygen in the gas mix above the level found in normal atmospheric air, and lets the fuel burn more efficiently.
Nitrous oxide is also incorrectly called 'NOS' among racers after one of the first companies to provide nitrous systems, Nitrous Oxide Systems (http://www.nosnitrous.com/). This is normally sounded out by letter ("en-oh-es") by pro mod drivers, although some pronounce it as a word (like "naws"). Today, there are several competing companies in the field, including Compucar, Top Gun, Nitrous Express, Nitrous Works, Cold Fusion, Nitrous Pro Flow and Edelbrock.
Nitrous systems can increase power by 35 to 1,200 hp (30 to 900 kW), depending on configuration, and are usually built in one or two stages. All Pro Mod cars and some Pro Steet cars use three stages, for additional power.
On the starting line, the drivers release a white plume of steam, which is called a nitrous purge. Most nitrous vehicles have a device called a purge valve which primes the system for use during the race. Some vehicles have one purge valve, some vehicles have two, and other vehicles have one purge valve with a dual outlet.
Types of nitrous systems
There are three types of nitrous systems: "Dry", "Wet", and "Fogger". A nitrous system is primarily concerned with introducing fuel and nitrous into the engine's cylinders, and combining them for most efficient combustion.
"Dry" nitrous system
In a "Dry" nitrous system, extra fuel required is introduced through the fuel injectors, keeping the upper intake dry of fuel. This property is what gives the "Dry" system its name. Fuel flow can be increased either by increasing the pressure in the fuel injection system, or by modifying the vehicles' computer to increase the time the fuel injectors remain open during the engine cycle. Once additional fuel has been introduced, it can burn with the extra oxygen provided by the Nitrous, providing additional power.
"Wet" nitrous system
A "Wet" nitrous system introduced the fuel and nitrous together, causing the upper intake to become wet with fuel. However, the intake must be designed for wet flow (for example, carburetors also require wet flow intake), as distribution problems or intake backfires may result. Dry-flow intakes are designed to contain only air, which will travel through smaller pipes and tighter turns with less pressure, whereas Wet-flow intakes are designed to contain a mixture of fuel and air. "Wet" nitrous systems tend to produce more power than "Dry" systems, but are correspondingly more expensive and difficult to install.
"Fogger" nitrous system
A "Fogger" nitrous system introduces nitrous and fuel directly into each intake port on the engine. Normally, these systems combine nitrous and fuel through a fogger nozzle, which mixes and meters the nitrous and fuel delivered to each cylinder individually, allowing each cylinder's nitrous/fuel ratio to be adjusted without affecting the other cylinders.
A Fogger system is the most powerful and efficient type of nitrous system, due to the placement of the fogger nozzle in each runner, as well as the ability to use more and higher capacity solenoid valves. A Compucar Fogger kit can go as high as 1,100 horsepower (820 kW) with only one stage. Fogger systems are also one of the most complex and expensive systems, requiring significant modification to the engine, including adding a distribution block and solenoid assembly, as well as drilling, tapping, and building plumbing for each cylinder intake. These systems are most often used on racing vehicles specially built to take the strain of such high power levels. Vehicles running one fogger nozzle per cylinder is said to be running "one fogger." These are very common on one-stage systems. Vehicles running two fogger nozzles per cylinder run "two foggers." These are used on dual stage kits. Vehicles running three foggers run on three stages of nitrous oxide.
Early pro mods
Most of the early pro mods ran nitrous. Many still run nitrous today. Some of the early nitrous pro mod users were Carl Moyer, Scotty Cannon, Bill Kuhlmann, Robbie Vandergriff, Scott Shafiroff, "Killer" Brooks, Wally Bell, Donnie Little, Charles Carpenter, "Animal Jim" Feurer, Mark Eldridge, Sonny Tindal, Terry Leggett, Norm Wizner, Bill Neri, Mark Carter, Tom Mauney, and others. Some of these drivers still run today with the nitrous and others have retired. Cannon, Kuhlmann, and Mauney now run blowers.
Pro Street nitrous drivers
Nitrous oxide was also used in Pro Street. Such nitrous pro street drivers included Max Carter, Mike Moran, Tony Christian, Danny Scott, Kenny Anderson, Mark Tate, Rick Dyer, and more. Anderson later switched to a blower. Stan Shaw and Rod Saboury were competitive running with a naturally aspirated motor.