Nitrous oxide engine

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A nitrous oxide system (NOS) is an upgrade for an internal combustion engine that makes more power by adding oxygen from nitrous oxide (N2O) during combustion. When N2O breaks down in the engine, it releases extra oxygen that lets more fuel burn, producing more heat and pushing the pistons harder.

Nitrous is stored as a liquid and turns into gas in the intake. As it vaporizes, it cools the air/fuel charge, which makes the air denser and helps the engine take in more air. The decomposition of N2O also raises combustion temperature, contributing to increased performance.

There are two main types of nitrous systems: dry and wet. In a dry system, nitrous is delivered alone and extra fuel is provided by the engine’s fuel system. In a wet system, nitrous and fuel are delivered together to the intake, giving a richer air/fuel mix.

Delivery methods, of which there are four common types, are used to introduce nitrous (and sometimes fuel) into the engine:
- Single nozzle: nitrous (or nitrous/fuel) enters through one nozzle, usually in the intake tract.
- Direct port: multiple nozzles place close to each intake port for each cylinder, offering precise distribution.
- Plate: a plate sits between the throttle body and intake with drilled passages to spread the mix.
- Bar: a hollow bar inside the intake plenum delivers nitrous through holes along its length.

Most systems are dry, but all four delivery methods can work in dry setups. Wet systems can be used with carbureted or fuel-injected engines. Bar systems are typically dry because fuel distribution with a bar is harder to manage. Some designs even use gaseous fuels like propane or CNG, which keeps the system technically dry.

Nitrous systems can use one or more stages of nitrous, with progressive delivery units controlling how quickly the nitrous (and fuel, in wet systems) is added. Progressive systems start with a small amount and ramp up power gradually to reduce stress on the engine and drivetrain. A purge valve may be used before activation to clear liquid nitrous from the lines so the right amount reaches the engine instantly.

Using nitrous places greater stress on the engine due to higher cylinder pressures. To avoid damage, you must strengthen engine components and carefully tune fuel delivery and nitrous flow. Nitrous can also cause issues with automatic transmissions because of the extra torque.

On the legal side, nitrous oxide use is restricted or banned for street driving in some countries. Regulations vary by region and racing body, with many sanctioning bodies prohibiting nitrous in professional drag racing, though it may be allowed in certain classes or events.

A brief history: nitrous oxide was used in some WWII aircraft to boost high-altitude power. In cars, the term NOS comes from Nitrous Oxide Systems, a pioneering brand. The term “nitro” is sometimes used informally, though it often refers to nitromethane, a different fuel.