How Nitrous Systems Work

Nitrous Oxide systems are arguably one of the most recognized big power adders that you can install on your Mustang. Popularized through movie and television, along with the marketing efforts of certain brands, have made “NOS” synonymous with added power and speed. But while many people know of nitrous systems, not nearly as many know how or why they work. In this article, we’ll get into the details on the different components of a typical nitrous system, how they work together to add power to your car, and also get into some of the optional components that can help keep your nitrous system and vehicle safe.

What is Nitrous Oxide?

Before we get into the mechanics of a nitrous system, let’s talk about the science behind nitrous oxide, what it is, and how it works to increase power.

Nitrous oxide is a colorless, non-toxic gas with the formula N2O. Often times referred to simply as nitrous or laughing gas, this gas has uses several uses, including in the medical field as an anesthetic and analgesic, in the food and consumer goods industry as a propellant, and as it relates to this article, for use in internal combustion engines to improve performance.

By itself, nitrous oxide is inert at room temperature and has very few reactions, making it easy and relatively safe to package and distribute. In the case of automotive use, nitrous oxide is stored as a liquid gas within a high pressure bottle, usually in quantities of 10 or 15 lbs for most applications, though smaller and larger bottles are available for special applications.

How Does Nitrous Oxide Increase Power?

An internal combustion engine produces power by burning a mixture of fuel and oxygen. Generally speaking, increasing the amount of fuel and oxygen into the combustion chamber increases the amount of power that can be produced. Superchargers and turbochargers accomplish this by forcing more air into the intake and the fuel system adjusting to increase the amount of fuel injected.

With nitrous oxide, injecting the gas into the air intake of the engine increases the amount of oxygen beyond what air normally contains. In addition, as the nitrous oxide changes from its stored, liquid form to a gas, the expansion and evaporation causes a significant drop in temperature in the vehicle’s air intake, resulting in a denser charge, which in turns means more air can be added to the mixture.

How is Nitrous Oxide Injected Into An Engine?

Nitrous oxide can be injected into a vehicle’s engine through various means, all of which result in at least nitrous being added to the engine’s intake charge, with some configurations adding fuel to the intake as well. Nitrous systems that inject only nitrous into the air intake are often referred to as “dry” nitrous systems, whereas nitrous systems that inject a combination of nitrous oxide and gasoline into the intake are referred to as “wet” nitrous system (a result of the “wet” mixture by adding fuel). In a dry nitrous system, the additional fuel requirement needed to maintain an appropriate ratio with the added nitrous is accomplished through the existing fuel system.

In both dry and wet nitrous kits, the injection of the nitrous or nitrous/fuel mixture is accomplished either through one or more nozzles in the intake piping, generally referred to as a “nozzle system”, or through injection directly into the runners of an intake manifold, referred to as a “direct port” system. A nozzle system is generally easier to install as it requires installation of only one or two nozzles, whereas direct port systems require installation of a nozzle per cylinder, along with the associating plumbing, hoses and rails or distribution blocks. However, because of the increased nozzle count, direct port systems can typically offer significantly higher amounts of horsepower – most single nozzle wet kits max out around 200-250 horsepower, while some direct port systems support up to 800 additional horsepower.

Regardless of the delivery mechanism or wet vs dry nitrous kits, one common component amongst them all are the nitrous solenoids. These solenoids are responsible for “opening up” or allowing the nitrous to flow from the bottle into the nozzles and ultimately into the intake. These solenoids act on an electrical signal indicating that they should open or close. In most kits, a single nitrous solenoid is used. In the case of wet nitrous kits, a second fuel solenoid is used to introduce fuel into the mixture. For direct port and multi-stage nitrous systems, it is common to see 2 or more of each solenoid in use.

When is Nitrous Used?

You’ve probably seen it in the movies or on TV. A car is equipped with a nitrous system, engaged in a race or getting away from the police. What does the driver to do get that extra bump and get passed their competition or away from their pursuer? They hit a button on their steering wheel that gives them an instant boost in power and they win the race or escape with ease.

This sounds great, and honestly, like a ton of fun. However, nitrous can be dangerous and do some serious damage if not used properly, and simply engaging your nitrous system with a button on the steering wheel, while it can work, is not necessarily the best option. If you inject nitrous at too low of an RPM, or at times other than full throttle, the result can be disastrous.

To help combat this, most nitrous kits come packaged with an arming switch, which turns the whole system on and makes it available for use, along with a full-throttle switch. A full throttle switch is a mechanical switch that you place either on your throttle linkage or by your gas pedal, adjusted to engage only when the throttle is at the wide-open or full throttle position. When you’re at full throttle, this switch is engaged, which then sends a signal to your nitrous solenoid to open and inject the nitrous oxide into your intake. Once you are off of full-throttle, the switch disconnects and the solenoids close. No manual intervention needed!

Another common approach, and one that lets you dial in the nitrous injection, is to use a window switch. A window switch is an electronic control module that monitors your throttle position and current RPM. This module can then be programmed to send a signal to open the nitrous solenoids only when the throttle position is wide open and the RPMs are between a certain range.

Common Components in a Nitrous System

We’ve already touched on a couple of components common to nitrous systems regarding the delivery of nitrous, but let’s take a look at all of the parts that make up a typical nitrous kit.

The bottle

Every nitrous system needs some container to house the nitrous oxide. These specialty bottles are purpose-built to store and transport nitrous oxide liquid at extremely high pressures – up to 1,500 PSI. Commonly available in 10lb or 15lb sizes, these bottles feature a valve to release the nitrous oxide into the rest of the system, and for safety, they also include a pressure release disc. These discs are designed to break once a certain internal pressure has been release, typically around 2,000 PSI, and to safely relieve the internal pressure of the bottle. Failure to have such a device or a faulty disc in place could result in an explosion of the nitrous bottle that will likely cause significant damage to your vehicle and possible injury or death to anyone nearby.

Hoses and Tubes

Nitrous oxide is effective only when it is under high pressure – usually that pressure is in excess of 900 PSI. This means that to transport the nitrous from the bottle to the solenoid(s), and then ultimately to the nozzle(s) for injection into the air intake, you must use hoses and tubes capable of withstanding high pressures. Commonly, stainless steel braided lines capable of the high pressures associated with nitrous applications are used, along with hard lines made out of stainless steel tubing.

Depending upon the application and the location of the hose or tubing, different sizes are used. The largest diameter hoses are usually used when connecting the nitrous bottle to the solenoid, and then smaller lines may be used when connecting the solenoid to the nozzle.

Nitrous and Fuel Solenoids

The solenoids used in a nitrous system are one of the most important components. Solenoids receive an electronic signal indicating whether or not they should open. In a dry nitrous system, you’ll only have a solenoid (or solenoids) for the nitrous oxide line, while in a wet nitrous system, you’ll have solenoids for both nitrous oxide as well as fuel. When opened, the solenoids allow the release of the nitrous and/or fuel to flow through and into the intake. Nitrous and fuel solenoids are available in different sizes depending upon application, and brands produce different solenoids and configuration variations to provide the best performance.


One of the final components of the plumbing in a typical nitrous system is the nozzle or nozzles. Depending on your application, these nozzle(s) are installed in the intake tube for a traditional nozzle configuration, or in the intake manifold for a direct port configuration. When used in a dry nitrous system, the nozzle will have a single port to connect to the nitrous line. For wet nitrous systems, the nozzle will have ports for both nitrous and fuel, allowing the two to mix within the nozzle before injecting into the air intake.

Nitrous and Fuel Jets

Inside of the nozzles of a nitrous system are swappable pieces called “jets”. These jets have different diameter openings. With different sized openings, you can adjust the amount of nitrous and fuel introduced into your intake, and therefore tune the amount of additional horsepower provided by your nitrous kit. When comparing nitrous kits and looking to purchase one, you’ll likely see mentions of the max amount of horsepower supported, as well as the ability to configure it, for example, to add 75, 100 or 150 horsepower. This configuration and the amount of horsepower added is determined by the size and combination of the nitrous and, in a wet nitrous system, the fuel jets used.

Arming and Throttle Switches and Relays

In most cases, you don’t want your nitrous system always active and engaged, injecting nitrous into your intake. Instead, you only want that in certain cases, such as during a race. During other times, you want your engine performing as normal. To make this happen, you will need at least an arming switch for your nitrous system. The arming switch acts as a sort of gatekeeper – without the arming switch enabled, the rest of the nitrous system won’t engage.

In addition to the arming switch, you will also want a switch to indicate when the nitrous should be injected into the air intake. This is accomplished with a wide-open or full throttle switch. This switch is only engaged when your throttle is in the wide-open position.

Lastly, nitrous solenoids take a decent amount of power, usually around 15 amps. That amount of current exceeds what many automotive interior switches can handle. So instead, relays are often used to draw higher amperage power from your power source (your battery), and engaged only when a switch (like your arming switch or your throttle switch) are engaged.

Additional Components in Nitrous Systems

We’ve covered the components that are used in a basic, bare bones nitrous installation. However, for safety, convenience or configuration, there are other components that should be considered when installing nitrous in your Mustang.

Nitrous Bottle Heater

As mentioned previously, nitrous systems perform best when highly pressurized, around 900-1100 PSI. However, a cold or less-than-full nitrous bottle can result in much lower pressures. To account for this, heat can be applied to the nitrous bottle, causing the nitrous oxide liquid to expand and increase pressure. This heat can be applied through a bottle heater. Available as either a wrap that can be strapped around the bottle, or integrated into a bottle bracket, a bottle heater will use an electrical current to heat the nitrous bottle. However, it’s important to monitor bottle pressure to make sure you don’t over-pressurize the system, so oftentimes a bottle heater is installed in conjunction with a nitrous pressure gauge and/or a nitrous pressure safety switch.

Nitrous Purge Kit

One important aspect of a well functioning and safe nitrous installation is ensuring a consistent delivery of nitrous. Changing bottles and using your nitrous system can result in air entering your nitrous lines. A nitrous purge kit allows you to open your nitrous system and expel any built up air from the line. Typically connected to a switch in the interior of your Mustang, the nitrous purge solenoid works very much like a regular nitrous solenoid, but instead of injecting the nitrous into your intake, it is expelled into the atmosphere. Opening the purge system a couple of times before use helps eliminate air in your system to improve performance, as well as looking pretty cool in the process. Most nitrous kits do not include a purge solenoid or associated parts, so keep that in mind as you are building up your nitrous system.

Nitrous Filter

Just like any other gas, nitrous oxide is susceptible to contaminants. These contaminants can wreak havoc on a nitrous system, particularly with the nitrous solenoids. Because the orifices in a nitrous solenoid are so small, contaminants can easily clog a solenoid, reducing the amount of nitrous being injected into the intake, thus resulting in lower performance, especially over time. To help alleviate this, many manufacturers produce nitrous filters that can be installed inline with the main feed line of your nitrous system. These filters will help to trap the contaminants in your nitrous system before they make it to the nitrous solenoids. Having one of these filters can help ensure you maintain a high level of performance with your nitrous system, as well as improving the longevity of your solenoids. Overall, nitrous filters add insurance to your investment.

Fuel Pressure and Nitrous Pressure Safety Switches

Keeping things safe is always important, especially when working with nitrous systems. When using nitrous, maintaining the correct air/fuel ratio is absolutely critical. Running too lean can cause serious problems. Often times, a lean condition can be attributed to a drop is fuel pressure. A fuel pressure safety switch, or FPSS, can help here. A fuel pressure safety switch is a mechanical switch installed somewhere along your fuel line. If your fuel pressure drops below the level you’ve set for the switch, the switch will open, interrupting any electrical circuit that it is wired into. By wiring the FPSS inline with your arming switch, you can have your nitrous system automatically disarmed when fuel pressure drops.

Similar to a fuel pressure safety switch, a nitrous pressure safety switch will open when your nitrous system exceeds a certain pressure. This can be extremely helpful especially when used in conjunction with a bottle heater. Once the pressure in your bottle reaches an optimum pressure, the nitrous pressure safety switch can open the circuit with your bottle heater, effectively turning it off until the bottle pressure drops below your specified setting.

Remote Bottle Opener

Unless you are planning on using the nitrous immediately, it’s highly recommended that the valve on your nitrous bottle remain closed. But what happens when you’re driving, and happen to have a reason to want to enable and use your nitrous? Stopping, getting out, opening the trunk and opening the nitrous bottle isn’t a very effective solution. Instead, why not open your bottle with the flip of a switch from your driver’s seat?

Many manufacturers offer a remote bottle opener. This remote bottle opener usually replaces the hand knob for opening and closing the valve with an electric motor. This motor can be activated with a switch placed conveniently around the driver’s seat, making it easy for you to arm your system, open the bottle and enjoy the giggle gas, all without having to stop and get out of the car.


Understanding how much nitrous pressure you are working with is extremely important when it comes to safely using nitrous in your Mustang without causing damage. To help with this, installing a nitrous pressure gauge, or multiple, can give you vital information about your nitrous system. At the least, it’s usually recommended to have a gauge installed directly on the nitrous bottle itself. This allows you to see quickly, even when the bottle isn’t installed in the car, how much pressure the bottle is currently holding. A simple mechanical gauge can work just fine in this case, and many nitrous bottles include ports specifically designed to allow the installation of a gauge. Additionally, you may want to understand the pressure of the whole system, so many nitrous users also install a nitrous pressure sending unit just before the inlet port of their nitrous solenoid, and then having it connected to a gauge displayed in the interior of the vehicle. With this configuration, you can quickly see whether or not the bottle is opened and there is pressure inside the line.

Nitrous Window Switch

Basic nitrous installations use a simple arming switch in conjunction with a mechanical wide-open throttle switch. With this configuration, you can turn your nitrous system on and, while under full throttle, nitrous will be injected into the intake. For basic installs, this can work fine, but if you are looking for a safer installation and want more tunability, a nitrous window switch is your ticket. A nitrous window switch takes two signals from your engine – the position of your throttle and the RPM of the engine. With this information, the nitrous window switch can then be programmed to activate your solenoids only when you are under full throttle and while you are between a certain RPM range. So rather than always on while under full throttle, it can be setup to turn on only under full throttle AND while the RPM are between, for example, 3,000 and 6,500 RPM. This helps ensure you have adequate airflow in your intake to draw in the nitrous, and helps to prevent catastrophic explosions during backfires with a wet nitrous kit.

Additionally, some nitrous window switch support multiple stages. Common nitrous installations are what are referred to as single-stage – there’s a set amount of nitrous that is injected, and that’s it. A multi-stage kit allows drivers to have increasing amounts of nitrous injected into their engine at different intervals. So for instance, a window switch can be configured to open the solenoids to a nozzle configured for 75 horsepower between 3,000 and 4,500 RPM. And then from 4,500 RPM to 6,500 RPM, the window switch can also open up the solenoids to a second nozzle configured for an additional 125 horsepower, giving you a total of 200 horsepower at that RPM range. This lets you fine tune and “ease-in” to additional power introduced from you nitrous system.

Other Articles