Some of my favorite bad and dumb movies are the Fast and Furious films. They don’t take themselves too seriously, and the plots are so easy to follow that you don’t really even need to know how to speak English to enjoy them. Fast and Furious also introduced me to nitrous oxide, or NOS (though that’s technically a brand owned by Holley). I didn’t know how that worked. But then I learned and now I’m showing you.
The recipe for almost any combustion reaction includes fuel and oxygen, the latter of which your engine gets from air. But air isn’t very oxygen-dense (it’s 78 percent nitrogen), meaning much of the engine’s intake charge is basically wasted space. That’s where nitrous comes in.
In an internal combustion engine like the one in your car, a combination of fuel and air is ignited at high temperatures by either a spark (in the case of a gas engine) or by compression (in the case of a diesel engine). The expansion of gases from combustion drives the piston down (the power stroke) and drives the crankshaft, which eventually sends power to the wheels through a set of clutches, gear sets and shafts.
Or just a set of belts and wizardry, if you drive a car with a CVT.
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Nitrous oxide, or N2O, is made up of two nitrogen atoms and one oxygen atom. When heated to around 570 degrees Fahrenheit (gas heats up during compression and, of course, combustion), the chemical bonds holding the oxygen to the nitrogen will break, thus increasing the amount of oxygen present in the combustion chamber. With more oxygen available, you also need to inject more fuel to keep the air-to-fuel ratio optimal, which yields a more powerful explosion, which means more torque to the wheels and thus faster acceleration times. Yay!
In a way, it works a lot like a turbocharger – cram as much oxygen into the cylinder so you can stuff in more fuel for a more powerful explosion. Except instead of compressing the intake charge, nitrous changes its chemical composition.
But if oxygen is what is needed for combustion, why inject any other gas? Well, nitrous oxide is preferred over regular compressed oxygen because it packages well. Nitrous can be liquefied easily if it’s pressurized, while liquefying oxygen requires freezing it down to some ungodly temperature, hence why oxygen tends to be transported in compressed gas form. But N20 in dense liquid form takes up much less room and yields more oxygen per unit volume than compressed gaseous O2.
Plus it’s safer. Not inadvertently exploding yourself is always a plus.
Nitrous for a car is stored in a canister under pressure to keep it in a liquid state. Once it’s released into the motor, it comes out as a really cold gas. How much gas you use is controlled by jets in the nozzle of the container, which then affects the horsepower level.
Moderating the amount of nitrous that goes into your engine is also important because you can’t keep a constant supply of the gas flowing. An engine uses a shit-ton of oxygen, so you wouldn’t want it to run on full tilt or you’d run out in no time.
On top of that, because nitrous comes out as such a cold gas, it also cools the intake air, which increases the density and gives the engine more oxygen. Nitrous can also actually suppress the risk of early detonation because of how cold it can make things.
A nitrous system relies on the existing airflow into the engine to pull the gas into the intake manifold and into the cylinders. You want to be at full throttle when you use it because this lets the engine computer add more fuel so the air-to-fuel ratio stays ideal. Don’t want to be running lean, now.
So if you’ve got a manual, you have to make sure not to activate the nitrous when you take your foot off the gas to shift. If you do that, you’re risking an engine backfire. Generally, the best results occur when you apply nitrous early on off the line, because you get such a huge surge of torque.
There are a couple types of nitrous systems: dry systems and wet systems. Dry systems are where only nitrous is injected. These have to be used with electronic fuel injection because they use oxygen sensors in the exhaust to balance out the increased amount of oxygen in the cylinders with more fuel. Wet systems inject nitrous and fuel simultaneously, which keeps the ratio of air and fuel in check always.
This video is a good explainer:
Nitrous is a relatively inexpensive way to add horsepower quickly. The systems and kits I looked at on the Holley site were mostly under $1,000. But you should also keep in mind that nitrous shines brightest when used in bursts. So it would make the most sense if you use your NOS in drag races and in quarter-mile runs.
And a nitrous kit supplies a lot of what you need apply nitrous to your car, though we should note it doesn’t exactly make everything a plug-and-play operation. It includes:
The nitrous bottle, nitrous lines, nitrous solenoids, fogger nozzle and associated wiring. The bottle is normally mounted in the trunk and stainless steel braided lines are run into the engine compartment. They are connected to the solenoids that operate like an electric valve to turn the nitrous flow on and off. Then the solenoids are connected to the fogger nozzle on the intake manifold where the nitrous is actually injected into the motor.
But you can’t just plug it all up and expect it work flawlessly, as you’ve also got to make changes to ignition timing.
The air charge in the engine becomes very oxygen dense, which can cause the combustion in the cylinder to occur too early. It means that instead of combusting while the cylinder is at the top of its travel—like it’s supposed to—the combustion happens before that and will push the piston down before it reaches the top.
This is bad.
Preventing this involves retarding the ignition timing. Luckily, some nitrous kits come with software that will adjust timing. Motor Trend’s David Freiburger has a good video explaining it.
Each engine responds to the extra power differently. Before you install a nitrous kit (correctly and carefully, I might add), you also need to make sure that your existing hardware can handle the extra power. There will be extra heat and force in the pistons that the stock engine, drivetrain and cooling system might not have been engineered to handle.
That’s when shit goes boom. Let’s avoid that.