Nitrous Oxide

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MiataPower Dir
Nitrous Oxide


Page one deals with the basics in nitrous oxide.

Page two deals with all the different stuff and gadgets that goes into this.

Page three deals with common questions and calculations.

Page four deals with installation of a dry single fogger system.


  • Why nitrous?


Why would you want to put nitrous oxide injection in your car?

Because it's the easiest, most powerful and cheapest way to produce horsepower!

I get a lot of emails with questions about nitrous, "what's nitrous?", "how does it work?", "will it blow up my engine?", "how much does it cost?". The purpose of these pages is to answer questions like this, my goal is to have something here for everyone, from complete beginners to experienced nitrous heads.

The main reason that people want to put nitrous in their Miatas is that they want some extra power now and then. They don't want the high cost and complicated installation of a turbo or supercharger kit. Or they are complete power junkies like me and want the nitrous on top of the turbo!
These are all very good reasons to get a nitrous system!

"Is it complicated to install?"
A nitrous system is easy to install, you mount a bottle in the trunk, you route a small tube from the bottle to the engine compartment, you mount a few small things under the hood, you install an injector in the intake, you make a few electrical connections and you're done! That's all there's to it.

"How can this stuff make hp?"
Simplified you can see nitrous oxide as "Super air", it's just like air but with more oxygen in it. Engines produce horsepower by burning fuel, that means that the fuel (usually gasoline) reacts with the oxygen in the air. Nitrous oxide by it self doesn't give you any more hp, just more oxygen. The trick is that with more oxygen you can burn more fuel and thereby produce more hp!

"How do you use it?"
Some people think that you flip a switch and then the nitrous (and extra fuel) is flowing and you just hold on for dear life. That is not how a modern nitrous system works (or should work). The system actually contains three controls, the first one is that you have to open the valve on the bottle (usually in the morning and then you close it at night), the second one is an arming switch mounted somewhere in the cockpit. Unless that switch is on, nothing will happen under any condition. The third switch is usually mounted under the hood, next to the throttle. It's a small micro switch that closes (meaning it's on) when you push the gas pedal to the floor, it only activates when you have wide open throttle (WOT). When all these three controls/switches are "on", the nitrous and the extra fuel is injected into the engine. This makes a modern nitrous system very safe, if something isn't right (engine doesn't sound right, tires are spinning too much, the cops are approaching, ...), just release the gas pedal as you normally would and the nitrous will instantly be turned off. It can't be much simpler than that, every condition except WOT and the car will behave as if it has never even heard of nitrous, but push the load pedal to the floor and you'll have the ride of your life!

"Can the engine really handle it?"
Miata engines are very tough, it was originally designed as a turbo charged engine and can handle a lot of hp. "But nitrous isn't the same as turbo?", No it isn't, but most of the things that makes a good turbo engine also makes it a good nitrous engine. If you want to make a career at the drag strip, you will have to make some serious engine modifications (just as if you would use a turbo), but if you want an extra kick in the back when that pesky Mustang or Camaro is pestering you, the stock engine is just fine.

"Can I abuse the engine as much as I want to?"
No you can't. There are certain rules you have to follow if you want to live a happy nitrous life. The first thing you have to think about is, NEVER EVER let it run lean. A lean condition (meaning that there is not enough fuel for the available oxygen) is very destructive to an engine and especially when you're running nitrous. The temperature in the cylinder gets very high and the fuel detonates instead of burns. The probable outcome is melted pistons, burnt valves, blown head gasket, cracked head or other unpleasant things.
The next thing is, don't try to force your engine to do things it doesn't like. If you have a turbo or a supercharger or even nothing at all, it will not make much power at low rpms. Put in 5'th gear and slow down to 1000 rpm, now push the pedal to the metal and the car will start to accelerate, very slowly, because the engine doesn't produce much hp at that speed. Nitrous is completely different, as soon as you hit WOT (with the system armed) it will inject a fixed amount of nitrous and fuel. It doesn't care if the engine is at 1000 rpm or 7000 rpm, it will do the same thing. If you have the nitrous system set for 50 hp, it will add 50 hp even if the engine is at 1000 rpm. Since the system injects a fixed amount regardless of rpm, the lower the rpm, the more nitrous will burn per power stroke. At low rpm's that creates a very high cylinder pressure and can cause problems. The solution is simple, don't engage the nitrous (i.e. no WOT) at too low rpm. "How low is too low?". It depends on how much hp the nitrous is set for and which gear you are in. If you have a 50 hp setting, don't engage under 2000 rpm in 1-3 gear and not under 2500 rpm in 4-5. For a 75 hp setting increase each with 500 rpm. "This sounds dangerous!". No it isn't if you keep it in mind. If you feel that you want some extra security, it's easy to put in an rpm-switch that will block the nitrous until a certain rpm is reached.
The third thing you should think about is, don't hit it too long. It's the same thing as with turbo or supercharger systems, when they produce this wonderful power they also generate a lot of heat. Don't push the pedal to the floor and keep it there until you reach the rev limiter in 5'th. Long hard pulls generate a lot of heat and pistons and valves are sensitive to that. If you want to see how fast it goes, push it 99% (just before the nitrous engages) until it doesn't go any faster and then engage the nitrous.
One last thing, DON'T EVER engage the nitrous unless you are in gear with your foot OFF the clutch. Don't even try just to see if I'm right, your engine will reach 10000 rpm before your next heart beat and the result it NOT pleasant.
And related to that, if you are tinkering under the hood, keep the nitrous unarmed. If the engine is running and you accidentally engage it, see above. If the engine isn't running and you accidentally engage it, don't even think about starting it, even if you "hit" just for a millisecond. Unscrew your spark plugs and crank it for a long time.

"How do I prevent it from running lean?"
Either you have to run the nitrous on the safe side (i.e. very rich air/fuel mixture) or you have to get some gauges. A nitrous pressure gauge mounted on the bottle is a must because you need to see when it's time to refill. That gauge is also a good monitor for how lean you are going to be when you engage the system. If the car has been sitting in the hot California sun for several hours, the pressure can be 1200 psi (optimal pressure is 950 psi). If you then go out and "hit" it, you'll probably be running lean. That doesn't mean that you can't engage it, it just mean that you should do short bursts (a few seconds) and pay close attention to how the engine sounds. A really good investment is an oxygen sensor monitor. It connects to your engines oxygen sensor and will show you directly if you're running lean or rich or just right.

"Do I need anything more than the basic kit?"
Not really, but there are two things that I recommend. The first one is a bottle heater. It's a thermostat controlled heating element that you wrap around the nitrous bottle, it's very easy to install and unless you live in a place where the temperature is *always* above 85 F, it'll be the best investment you'll ever make. The air/fuel ratio is dependant on the nitrous pressure and the nitrous pressure is dependant on the bottle temperature. With a bottle heater to keep your pressure constant, you'll be a million times more happy with the system than without one.
The next thing is an oxygen sensor monitor, it'll give you piece of mind and you'll learn much more about how the system actually works.

"This sounds great, where do I go from here?"
The first thing you should do is to read the rest of these pages, several times! If you still have questions, don't hesitate to write me an email and ask, my email address is on the homepage.

"OK, I want one! What type of system should I get?"
It depends a little on your current configuration. Do you have a turbo or a super charger? How much power do you want? How much money do you want to spend? Do you mind taking the intake manifold off? The easiest and cheapest system is the single wet injector, it works with pretty much any configuration of your Miata and is simple to install. The only drawback is that with a normally aspirated engine (no forced induction) you shouldn't go above 60 hp or you might get distribution problems and/or puddeling. A more advanced system is to remove the intake manifold and put an injector in each intake runner, you get perfect distribution and it can handle as much power as you want.


  • How nitrous work


Nitrous oxide gives you two things, more oxygen and cool air. When the N2O is injected into the intake manifold it changes from a liquid to a gas and the temperature drops to -127 F. This makes the air in the manifold much denser. During the compression stroke the N2O breaks up into nitrogen and oxygen. The nitrogen cushions the combustion so it won't be too violent (if you inject pure oxygen your cylinder head will go into orbit) and the oxygen does what it's supposed to do (burn more fuel). The key here is to feed it enough fuel or you will get a VERY lean combustion (NOT good).




You can divide nitrous systems up in categories based on different criteria.

  • If you look at how the fuel is added, you have dry and wet systems.

  • If you look at how the nitrous is injected, you have single injector or direct port systems.

  • If you look at the way the nitrous is controlled, you have single stage, multiple stage and progressive systems.

Dry manifold

I had this type before. It just means that the nitrous is injected by itself into the intake manifold. Fuel is added by increasing the amount that the normal fuel injectors are supplying. This can be done by either instructing the ECU to add more fuel or by increasing the fuel pressure like most turbo and supercharger kits do. My kit did it by increasing the fuel pressure. Also of interest is that a dry system that adds fuel by increasing the fuel pressure is incompatible with turbo/supercharger systems that uses a rising rate pressure regulator. A dry system can use either a single central injector (that's what I had) or a direct port configuration. A direct port dry system with the proper ECU support would be a really good solution.

Wet manifold

This means that you inject both nitrous and fuel separate from the normal fuel delivery. Usually the fuel and the nitrous is injected through a combined injector (called a fogger at NOS).

Single injector

This actually refers to a single point of injection. It can be a fogger or an injection plate. Injection plates are mostly used on V8's but they do exist for other engines also. For our type of engine the most common type is to use a single fogger somewhere before the throttle body. The problem with single point injection is that the distribution of nitrous (and fuel if it's a wet system) between the cylinders can be less than perfect. In a wet system that means that the distribution of power between the cylinders will be uneven. In a dry system it means that the air/fuel ration will vary between them and that is really bad (and the reason I burned three valves).

On an engine with a fairly long intake tract, like the Chevy 350 TPI or Ford 4.6L, I can imagine that a dry system with single point nitrous injection works, but it doesn't on a Miata.

The problem with wet single injector systems is that you can get puddeling of fuel in the intake system. This seems to be more of a problem for V8's and not so much for small 4-cyl engines (I haven't seen any symptoms).

Direct port

With a direct port system you put (at least) one injector for each cylinder, that way there is no mixing between the cylinders and perfect distribution and air/fuel ratio can be archived. One thing to remember is that for a small engine like the Miatas is that there is a limit to how low you can go in power with a wet direct port system. If you feed the injectors directly from the stock fuel line it's about 75 hp and if you put in a pressure regulator you can get it down to 50 hp. A direct port system is also more complicated to install since it requires that the intake manifold be removed for drilling and tapping.

Single stage

A single stage system means that there is only on or off and that you inject the same amount of nitrous (and fuel if it's a wet system) all the time regardless of rpm or load. This makes for a very easy system, both to install and to understand. Single stage systems are also the most common. The problem with this kind of system is that the low end rpms limits how much nitrous you can inject and the engine will be starved (well, at least not showing its full potential) at the higher rpms.


You put several "normal" nitrous stages together and trigger them at different times. This type is most common in drag racing where you launch on the first stage and then enable more stages as speed increases. This is usually controlled by timers. The advantage over a single stage system is obvious, you can start to inject a safe 50 hp at 2000 rpm and then add a healthy 50 more at 4000 rpm for example. The down side is cost and complexity.

Progressive controllers

Here you start out with a "normal" nitrous kit (usually a port injection) and add an electronic controller. The controller opens and closes the solenoids about 20-30 times/second. By varying the duty cycle, it controls the amount of nitrous and fuel that is injected. There are several brands and types of this controller. Some modulate depending on the rpms, some on throttle position, some on time and the really advanced have a combination of these.



Last revised: Friday, February 02, 2007