deals with the basics in nitrous oxide.
deals with all the different stuff and gadgets that goes into this.
deals with common questions and calculations.
deals with installation of a dry single fogger system.
Why would you want to put nitrous oxide injection in your car?
Because it's the easiest, most powerful and cheapest way to produce
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
"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.
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
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.
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.
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).
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).
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
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.
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