Exploring Nitrous - Part One

Nitrous-oxide has been used by racing enthusiasts for decades and is one of the most respected forms of engine enhancement. Forget fumbling around with cam profiles, compression ratios and exhaust tuning – if you want a serious horsepower boost, nitrous-oxide is your no-fuss solution.

In this three-part series we’ll look at how nitrous-oxide allows you to generate more power, what you get in a typical aftermarket kit, some tuning issues and the general ups and downs.

Nitrous Oxide – How it Improves Performance

Nitrous-oxide (N20) is a non-toxic gas that comprises molecules made up of two atoms of nitrogen and one atom of oxygen.

From a performance perspective, the most important aspect of nitrous-oxide is its oxygen content. By weight, nitrous-oxide is 36 percent oxygen compared to air at just 21 percent. Furthermore, nitrous-oxide is around 50 percent denser than air. Combine these two factors and nitrous-oxide provides 2.3 times the usual amount of oxygen for a given induction volume!

What does this have to do with making your car to go faster, you ask? Well, the greater amount of oxygen provided by nitrous-oxide allows more fuel to be burned for each combustion cycle. This creates a higher cylinder pressure – and that’s where you get the eye-widening extra performance.

Note that nitrous-oxide is not a fuel. Enrichment fuel must be added separately to generate more power.

The Fight for Combustion Chamber Space When you inject nitrous-oxide into an engine it results in slightly reduced induction airflow. If a cubic foot of nitrous is injected into the engine it displaces approximately one cubic foot of induction air that would otherwise enter the engine. This means you lose the energy that could be released from this cubic foot of air, but – of course – the dense and oxygen-rich nitrous-oxide more than makes up for it. It’s a very worthwhile trade-off!

Early Use of Nitrous-Oxide

The first flurry of development using nitrous-oxide occurred during World War 2.

Aeronautical supercharger and water injection systems were flourishing at this time and when a combat aircraft needed to fly at a higher altitude and at greater speed, nitrous-oxide injection was sometimes employed.

It is said that up to 350 additional horsepower was found using nitrous-oxide on the Daimler-Benz V12 aircraft engine. Relatively few combat aircraft were equipped with a nitrous system, but the detailed development that occurred throughout the war was later put to use by racing enthusiasts.

Nitrous-oxide is also used as a mild anaesthetic and is available in medical level grades.

Contents of an Off-the-Shelf Aftermarket Nitrous System

There are currently several aftermarket manufacturers of off-the-shelf nitrous-oxide systems – these include NOS (Nitrous Oxide Systems), NX (Nitrous Express), ZEX and OzNOS. The kits marketed by these companies share the same basic ingredients. These are...

The Nitrous Bottle

At one end of a nitrous-oxide system is the storage bottle. The nitrous bottle can be constructed from aluminium or steel and its size varies depending largely on the amount of extra horsepower achieved (ie the size of the ‘shot’).

The nitrous bottle must be capable of withstanding massive internal pressures and many are protected from over-pressure by a vent valve. Most importantly, the bottle should meet local government standards for nitrous-oxide storage.

At the head of the nitrous bottle is a shut-off valve than is normally opened and closed by hand. Some systems have a remote in-cabin switch that opens and closes the valve. This valve should be left closed except when you expect to use the nitrous.

Nitrous Lines

When the bottle valve is opened it allows nitrous-oxide (which is stored at high pressure) to flow through a line that leads into the engine bay. This line must be steel reinforced, rated up to around 5000 psi and sufficiently shielded to avoid damage. Depending on the vehicle and application, the nitrous line can be run through the inside of the cabin or beneath the floor against the chassis.

Note that a blockage in the nitrous line will reduce power, so an appropriate filter should be installed near the bottle.

Nitrous Solenoid

When the nitrous line arrives in the engine bay it connects to an electric solenoid valve that’s specially designed for nitrous-oxide use. This solenoid remains closed until the system is activated and you need extra power.

Once opened, this solenoid allows nitrous-oxide to flow into the engine. The point of nitrous injection and the variety of nitrous nozzle can vary - and we will discuss this in detail later.

Fuel Enrichment Circuit

Simultaneous fuel enrichment is essential when the nitrous system is activated. The approach to fuel enrichment can vary depending on the type of nitrous system.

In a typical wet manifold system the nitrous kit comes with a dedicated fuel enrichment solenoid. This photo shows a nitrous solenoid alongside a fuel enrichment solenoid. As seen, the fuel enrichment solenoid looks similar to the nitrous solenoid except it is usually rated at lower pressure. This solenoid opens and closes the flow of fuel into the engine. Again, the point of enrichment fuel injection and the type of fuel nozzle can vary.

Some wet manifold systems are installed with an additional fuel pump paralleled to the existing fuel pump. A dedicated fuel pressure regulator is often included as well. Alternatively, some enrichment circuits draw fuel from the existing fuel system – but only in cases where there is adequate fuel system flow.

The fuel enrichment system operates at much lower pressure than the nitrous side of the system, so it is acceptable to use regular fuel hose for these lines. Steel reinforced lines are commonly used to provide more under-bonnet visual appeal.

Note that a filter must also be fitted in the fuel enrichment circuit. A fuel enrichment blockage will cause lean mixtures and potential engine damage.

Activation Electronics

The nitrous-oxide system - including the fuel enrichment circuit - is triggered when a minimum of two switches are activated.

An arming switch (which can be a simple in-cabin toggle switch) is used as a primary activation device. If this switch is not ‘on’ the remainder of the system will not operate. A secondary switch – a throttle position switch – must then be tripped to activate the nitrous system. The throttle position switch is usually set to trigger at wide-open throttle – when the driver wants maximum power.

Many systems also incorporate an rpm switch, which is typically configured to prevent the nitrous system activating at low engine speed. At less than about 2500 rpm the chance of nitrous-related engine damage is considerable. We will detail this characteristic later.

Nitrous Oxide Nozzles There are two main varieties of nitrous nozzles. The most basic design is a regular nitrous nozzle that passes nitrous-oxide only. This type of nozzle must be aimed so that its spray collides with the spray from the fuel enrichment nozzle. This is essential to ensure good mixing and relatively even cylinder-to-cylinder nitrous and fuel enrichment distribution. A more sophisticated nozzle is known as a "fogger". A fogger nozzle sprays nitrous and enrichment fuel from the same nozzle assembly. This design ensures the nitrous and fuel enrichment are well mixed and there is better cylinder-to-cylinder distribution.

Stick around for Part Two of this series - we’ll be exploring the different types of nitrous configurations and looking at nitrous tuning.