NOS: What is Nitrous Oxide for Cars | Using A Nitrous Kit (2024)

by Sebastian Cenizo /

Nitrous oxide, commonly called NOS, is a gas discovered in 1773 that is highly flammable - much more so than regular gasoline. Two particles of nitrogen for every particle of oxygen give nitrous oxide the chemical formula of N2O. Many people refer to it as NOS (an acronym for Nitrous Oxide Systems), but this is actually the brand name of a company, much like many people refer to tissues as Kleenex. Other brand names include Nitrous Express (NX) and ZEX - but these are all the same thing.

Nitrous injection is a form of forced induction like turbocharging or supercharging. It is stored in liquid form and released as a gas under high pressure. The oxygen only splits from the nitrogen once it gets to the heat of the engine, which means that said oxygen is very dense and that it can be injected into the intake or the combustion chamber without any risk of pre-detonation. As a result, it can produce more power than your typical gas and oxygen mix, which is exactly what those who add nitrous to their cars want.

Now that we know what it is, how does nitrous oxide work? Well, if you're a dentist, you'll know that nitrous oxide is commonly referred to as laughing gas. Its earliest uses were as an anesthetic before German engineers in World War II used it to enhance the performance of airplanes at high altitudes. Turbocharger technology soon overtook nitrous systems as the preferred method of increasing air density, but as drag racing started to really take off in the 1950s, nitrous was again explored as a means of boosting cars' performance.

Various methods are available, but the basic principle is to inject the nitrous oxide into some area of the intake system, or directly into the combustion chamber. This cools the intake air and increases density, resulting in more power and a higher rate of combustion. Essentially, the basic reason to inject nitrous oxide is to increase the amount of oxygen in the combustion chamber, allowing for more fuel. When the liquid nitrous is released from the canister and expands into a gas, it cools and thus becomes denser, and once in the combustion chamber, the oxygen splits from the nitrogen allowing for more fuel and preventing premature detonation. More air = burning more fuel = more power. This is basic engine mechanics.

There are two main ways of injecting nitrous oxide into the engine, but each has the same goal of increasing density and forcing more power out of an engine, whether it be a gasoline engine or a diesel-powered one. Both turbocharged and naturally aspirated engines can benefit from this, and it can be used on supercharged cars too. Even your lawnmower could probably run on nitrous for a time, but we wouldn't recommend this. These are the most common types of nitrous systems used:

• Wet injection: A wet nitrous kit sees the nitrous oxide injected into the combustion chamber simultaneously with additional gasoline (or other fuel) through the same plate or nozzle that supplies the fuel. This mixture is called 'wet' because it mixes with the extra fuel that comes from a separate fuel pump, alongside the existing fuel injection system. A wet system is typically used on carburetted engines, but as a relatively simple way of getting the nitrous into the combustion chamber with minimal modifications, it is popular on regular EFI (electronic fuel injection) systems too. The size of the plate or nozzle will determine how rich the mixture is when it enters the combustion chamber.
• Dry injection: This system works by using the existing fuelling system (either carburetted or fuel injected), to supply the gas or diesel while the nitrous is injected into the intake separately. This means that the plate or nozzle (the latter is also known as a jet) only supplies nitrous oxide and does not mix with regular fuel until in the combustion chamber. Here, just as with the wet system, a switch is used to activate the system, but the amount of N2O is controlled by either the fuel injection controller or the ECU, allowing the EFI system to calculate when to spray and how much to inject. More advanced nitrous oxide injection systems can make this N2O injection progressively greater or progressively lesser. For example, if you are using nitrous to speed up the rate at which your enormous aftermarket turbo spools up, you will not need as much (or any) nitrous as you get to higher rpm.

In both systems, tuning is an absolute necessity and you cannot simply add a high concentration of laughing gas and expect reliable performance gains. You need to provide more fuel for the additional oxygen released from the N2O mixture to safely combust, or you will actually have a lean reaction and cause premature detonation, or pinging. Once you've got your needs figured out, you can decide to go with a single nozzle nitrous kit, spraying the gas into the intake, or multiple smaller nozzles for each cylinder or bank of cylinders, depending on the application.

Some setups will have two-, three-, or four-stage kits. These systems will either start off small and finish with a big shot of N2O (typically a naturally aspirated engine) or start off big (for example, to get the turbo spooling) and end with smaller shots as the engine relies more on the turbo. These types of nitrous oxide cars are typically seen in drag racing. A car that runs purely off a nitrous oxide engine is rare and will typically require frequent rebuilds.

In the early 2000s, a movie called The Fast and the Furious hit our screens and introduced many to the import tuner culture and cars with NOS. In the film, a nitrous boost was conveyed as the best way to increase performance and win a race. The rest was history, but while the film shone a light on the little-known systems, it also misinformed viewers who believed that nitrous makes your vehicle faster (it can improve acceleration but cannot increase the ultimate capability of an engine, only help it reach that point sooner) and that its regular use has no repercussions beyond causing "danger to manifold". While we laughed at the fact that the floor of Brian's car fell off, there was some accuracy to the warning. Too much pressure can indeed "blow the welds on the intake" and "fry the piston rings", but these dangers are not only present when you put too much nitrous in the system.

Increasing the performance of the engine at the wrong point in the rpm range can bend or snap connecting rods and forcing more performance out of an engine that was never designed to take this level of added strain for a sustained period has obvious negative side effects. The block itself can also deform, the cylinder head can warp, and without enough fuel, a "direct port nitrous" kit, as Jesse famously spoke of, can cause the aforementioned pinging, leading to catastrophic engine failure. Furthermore, you may find that the legality of a nitrous kit of street use is non-existent in your region, so you could get your car impounded for simply having a kit fitted, even if you're just cruising on the highway. So is it worth it? You decide:

Sebastian Cenizo

Deputy Editor

Contact Sebastian @sebz_tsc @sebz_7