This page explains some of the features and benefits of running nitrous oxide on your car. Hopefully,
these will be
useful for those considering a nitrous installation, or just wanting to know what’s up.
There are many different philosophies and opinions regarding the proper nitrous system. Please e-mail
if you have positive question or suggestion that could improve safety or contribute to quality and
HOW NITROUS WORKS
Nitrous Oxide, Ny-Trous plus, NOS, Spray, Juice, Shot, Squeeze, Bang, Blow, Jizz, Laughing Gas
It is a colorless, odorless gas composed of two (2) nitrogen atoms bonded to one (1) oxygen atom. The
abbreviation for nitrogen is N, and O for oxygen. The proper abbreviation for one nitrous oxide molecule
is N2O. This where
the familiar phrase “N-2-O” comes from.
Nitrous Oxide is an oxidizer that is used as a carrier for oxygen. Mixed with the right ratios of fuel, and
fed into the intake, it
provides additional combustible material into the cylinders, creating more power. There are many ways
to get the nitrous
and fuel into the engine, the following describes typical applications that have proven successful.
The nitrous is compressed to high pressure (900-1100psi) in a tank, in liquid form. From the tank
(typically fastened down
tightly in your trunk), a hose runs up to the engine bay. From there, an electrically controlled (like, by a
button you push)
valve called a solenoid is used to release the nitrous into the motor when you request it. At the same
time, a fuel line in a
"wet system," is controlled by another solenoid, and releases fuel into the motor. This provides the basic
mechanism for the
WET - VS - DRY
You may have heard the terms "wet kit" and "dry kit.".
A "wet system" is a nitrous system that mixes both nitrous and fuel, and feeds it (in a "Spray") into the
intake. A "dry system"
only feeds nitrous into the intake, and tricks the existing fuel system to add the fuel.
As mentioned, there are several ways to feed the nitrous and fuel into your motor. Here are brief
descriptions of them.
THROTTLE BODY PLATE
This is a 1/2" thick plate that's mounted between your throttle body and intake manifold. Both nitrous
and fuel lines are
connected to it (so it's a wet setup) and the plate combines them and sprays into the intake
A nozzle can support either a single line for nitrous, or a pair of lines for nitrous and fuel, and sprays a
fine mist into the
The ultimate setup..
Each port is tapped and threaded specifically for a nozzle at each cylinder. nitrous and fuel lines to
spray directly into the
cylinders. This setup typically provides the most horsepower for extreme race applications.
Of course, you don't want the system to be running all the time - a 10lb bottle will last you less than a
minute, if it's open.
Typically, you want the system triggered on while you're at the track, at WOT (wide open throttle), and
at relatively high rpm's
(see "Safety" for why). To make that happen, you'll typically want to wire, in sequence, several switches.
I won't describe the
specific wiring here, but you'll have some or all of the following:
1. Arming (On/Off ) switch.
2. WOT switch is a micro switch installed on the throttle system, that activates the circuit only when your
foot is on the
floorboard. 3)pushbutton in the car, probably on the shifter 4)"Window Switch" (see "Safety" for details)
that closes the
circuit only when the engine RPM is between a certain range (like 3000-6000) that you decide is
acceptable 5) Fuel Pressure
The system to trigger described above is a basic "single stage" setup. The nitrous is either on or off,
and when it's on, the
full volume dictated by the jets is sprayed into the engine. There are other applications that are full race
or multiple stage
nitrous system that require more detailed management at higher rpm, with time-based systems, which
delay the nitrous flow
for some time after you launch, etc.
These Nitrous controllers are a great addition to any nitrous system and can help to safeguard the
engine from Lean-
Use all the safety mechanisms you have available. They are cheap and very effective. Components
such as Fuel Pressure
safety Switch, Rev limiters, EGT sensors, Window switches, etc. are relatively inexpensive ways to
protect your investment.
WHAT CAN GO WRONG?
Well, a lot can go wrong, but hopefully you'll have adequate safety mechanisms built in to protect your
motor when it does.
The main thing that can go wrong is adding nitrous into your engine without compensating fuel. This
extreme lean condition
is disaster for the engine, and you're not likely to get a second chance - at least with the same engine.
extra fuel without nitrous is not particularly bad for the engine, so you can imagine, it's safer to start with
the car running
rich (too much fuel), then lean it back from there. Some examples of problems you might encounter
* Ignition RPM Limiter
The rev limiter is implemented by cutting the signal to the fuel injectors so the cylinders have no
combustion. If you're
running a dry system, which depends on the fuel injectors to provide compensating fuel for the nitrous,
losing fuel this way
is the ultimate disaster. An after market ignition will typically implement the rev limit by cutting off spark
rather than fuel,
which is a much safer implementation of the rev limit. Typically, you'd get your stock PCM programmed
to set the rev limit up
higher than you'll ever expect to go (like 7000RPM), and use the setting on the after market ignition as
your actual rev limit.
This electrical device provides an open or closed circuit based on the engine being between two RPM
"window") that you chose, so that you'll only flow nitrous in this range. Why would you do that? Well, for
two very different
1. At low RPM, think about what's going on: you're spraying nitrous into the intake at a constant flow.
That is, the nitrous
bottle and solenoids have no idea what RPM you're at, and they're just pushing it into the intake at a
constant volume. Inside
the engine, though, the nitrous and fuel combination is being sucked into the cylinders during every
stroke. The net result
is that at low RPM, you're getting far more of the mixture into the cylinders. At 3000 RPM, for example,
you're getting twice
the amount as at 6000 RPM. So, you can imagine that running nitrous at, say 1000 RPM, is far more
stressful on the motor as
at 3000 RPM, and typically causes a "nitrous backfire" - meaning that the nitrous/fuel combination can
explode in the intake
manifold (rather than the cylinders) - a bad thing. So that's why you don't want the system triggered at
2. At high RPM, the situation is easier to explain. Given the discussion of the rev limit above, you may
just want the nitrous
system to cut off before hitting that rev limit. If you've got a stock ignition, you certainly want a window
switch. If your rev
limit is implemented by an aftermarket ignition, it's perfectly safe for the motor to run nitrous during the
rev limit. It's not
particularly easy though, on your transmission or clutch to have all that power during the shift, which
may be a reason to
keep the window switch set a bit before you shift.
FUEL PRESSURE SAFETY SWITCH (FPSS)
This is a device that's plumbed into the fuel system, and provides an open or closed circuit based on
availability of fuel
pressure. It can be used in the triggering circuit to make sure the system isn't on when you've got a fuel
you only use it to switch off the nitrous solenoid; turning off the fuel solenoid as well can start a cycle of
solenoids on and off while the pressure raises and drops in the fuel system when you're switching the
solenoid on and off.
Let the pressure build up in the fuel lines when you open that solenoid, and when it's high enough, the
nitrous solenoid will
open. The switch can be used whether you've got a wet or a dry system. You can adjust the pressure at
which it triggers by
using an allen wrench on the back of the switch (loosen the screw lowers the pressure threshold).
You want to set the pressure on the FPSS, such that if the pressure drops about 10psi the nitrous
system will shut off. On a
wet EFI system, this will be around 33psi, and on a dry system I'd leave the switch just above stock, say
To set the threshold pressure, you've got a couple options:
1. Connect enough plumbing so that you can have the FPSS installed at the same time as a fuel
pressure gauge. Turn the
key on to pressurize the fuel system, then turn it off. As the fuel pressure bleeds down, monitor the
continuity across the
FPSS contacts (disconnect them from the rest of the nitrous system) and when the pressure reaches
the level you're
interested in, adjust the screw on the back so it just balances back and forth between the continuity
2. You could use an air compressor, with the appropriate fitting for the FPSS. Remove the FPSS from
the car, and thread it
onto the compressor. Set the compressor for the pressure of interest, and measure continuity as above.
If you can't do option #1 above because you don't have two available ports, first thread in the pressure
gauge, and cycle the
key. Then time how long it takes for the pressure to bleed down to the correct level. Then disconnect
the pressure gauge,
install the FPSS, and do the process against the clock rather than the pressure.
A nitrous/fuel mixture increases the burn rate in the cylinder, and typically adding a few degrees of
timing retard is
recommended for safety. A rule of thumb is two degrees per 50hp of nitrous, but this will also reduce the
When I tune my system, I monitor engine knock, and retard the timing only enough to eliminate the
knock, which is usually
about one degree per 50hp. At the track, under harder conditions (actually pulling the weight of the car,
outdoor temperatures, etc) I'll add a degree of retard.
HIGH OCTANE FUEL
High octane gas (e.g. 100 or more, unleaded) will also slow the burn rate in the cylinder. This will
provide another way,
similar to retarding timing, to avoid knock. I only use nitrous on a 50/50 mix of 92 octane pump gas and
100 octane racing
gas. Make sure it's unleaded, of course, or you'll destroy your O2 sensors.
By the way, watch out for Octane Boost claims. Typical claims are "8-10 points of octane boost for a
tank of gas." You should
be aware that these "points" are tenths of a point of octane as you'd purchase at a gas station. So the
above example will
raise your octane from 92 to 92.8 or 93, not 100-102 as you might think.
Don't assume that if high octane fuel helps on nitrous motors, that it'll help your naturally aspirated
motor too. A naturally
aspirated motor is tuned for a particular octane of gas; adding more doesn't help one bit. Save your
A simple part, but essential in any nitrous system. This filter is added in-line to your nitrous line, between
the tank and the
solenoid. Install it as close to the solenoid end as is convenient. It will trap any small particles that may
come through the
line, much like a fuel filter. A common solenoid failure is due to some particle jamming it open.
Your fuel system is the most important part of the system. As I hope is clear by now, the worst scenario
in a nitrous system is
a lean air/fuel mixture. The solutions to a good fuel system depend on the type of nitrous system you're
On a wet system, you simply need to ensure that your fuel system can supply adequate fuel, at
standard (~45psi at WOT)
pressure. A stock f-body fuel pump can usually supply enough fuel for around 450 total horsepower to
the motor; any more
and you want to get a larger pump. Much more than 650hp and you'll want larger fuel lines as well.
On a dry system, not only do you want adequate fuel like the wet system, but on an typical setup the
fuel is added by raising
the fuel pressure, which forces more gas through the injectors. In this scenario, it's typically
recommended that you replace
the stock fuel injectors with better quality (not higher rating, just better, like Bosch) injectors. These
injectors are able to
handle the increased fuel pressures necessary.
Generally you want to use copper spark plugs or iridium as opposed to the stock platinum ones. You
also want to reduce the
gap from the stock 0.050" down to 0.035"-0.040". I've received a couple notes on why you use a smaller
gap. "The reason you
want a smaller gap is because of ionization. If you change from the typical air (78%nitrogen, 21%
oxygen)/fuel ratio, a given
gap requires more energy to ionize the mixture, resulting in less energy in the spark, if you even get a
spark. You could also
increase the coil voltage instead of decreasing the gap, but I think using a smaller gap would be
preferential since the spark
time will be smaller." and also this message: "The reason that you will close the gap on your spark plugs
is because when
nitrous is added, it raises the cylinder pressure, much like a supercharger. Therefore "blowing" the
spark out. When you
close the gap it cannot put out the spark as easily."
I mentioned failed fuel or nitrous solenoids doing damage. Some of the issues here may be hard to
cover with only other
safety devices. I recommend you wire your solenoids with spade clips, so you can easily disconnect
them, and test them on
a regular basis. Simply disconnect them from the rest of the wiring, then ground one side, and connect
the other side to 12V,
and listen for the click-click to make sure they open and close. Some folks will also use two nitrous
solenoids, in-line, which
will ensure that both would have to fail before the flow would fail to stop. Of course you still need to test
this setup, to
ensure one isn't stuck open.
All of the kit systems will come with a couple tuning setups, labeled "50-shot", "100-shot", etc. These are
tuned to provide
35, 50, 75 or other horsepower amounts, usually measured at the crank (i.e., measured on a chassis
dyno you'll get a bit
less). I consider these a starting point, and certainly good for your first passes (hopefully you'll make
these with the lowest
power, until you tune the system up). Once you've got the system installed and functional, though,
tuning it is paramount,
before running any serious power through it. I really recommend you do this tuning right away, even
though the temptation
will be strong to just go out and enjoy the power. This is the time you're very likely to do some serious
damage to the motor,
it's important to get it set up right.
I'm not going to go through a bunch of details on tuning here, other than to mention some ideas. You've
got a plumbing
system to test, as well as an electrical system. You'd like to test each component of both systems, to
verify that it's correctly
doing it's job. I suggest doing most of this in your garage, with the nitrous and fuel lines removed from
the intake, and
pointing (or held) into a rag. Keep in mind the nitrous line will give a good kick under pressure, so don't
just leave it loose to
whip around. You can test your WOT switch easily enough, your window switch (maybe set the window
range at a lower rpm
for the test, so you don't have to rev up to your red line). To test your fuel pressure switch, you'll need
to verify it's got a
closed circuit when the engine is running (showing adequate pressure), but you'll also want to verify that
it opens the circuit
as fuel pressure drops. There are a couple ways to do this. On my car, the fuel pressure bleeds off at
about 2psi per hour.
So if I switch the engine off, I can use an ohm meter to check continuity across the FPSS connections,
and within a couple
hours it should switch off. You can also test the FPSS on an air compressor, by generating the pressure
you want for the
FPSS, and monitoring that it switches at the right point.
For the plumbing, you of course want to verify that there are no fuel or nitrous leaks in the system. You
should be able to
leave your nitrous bottle open for hours without losing bottle pressure. On the fuel side, of course a fuel
leak may be the
most disastrous possibility, so check this first by pressurizing the system (turn the key to "acc" but don't
start the car) and
feel around all the fittings.
I haven't listed all possibilities, but hopefully given you an idea of where to start testing. Once everything
seems to check
out, put in a set of 50hp jets, and move out on the track.
All nitrous systems use "jets" inserted in the fuel or nitrous lines to limit the flow. These jets have
openings of a specific
size, measured in thousandths of an inch. So a "35 jet" is a jet with a hole drilled 0.035" through it.
Increasing a nitrous jet
size will make the system run more lean, increasing the fuel jet size will make the system run more rich.
There's also a good web site with a jet size calculator on it for a wet setup (where you're metering the
fuel and nitrous
yourself). It will give you jet sizes based on desired horsepower, fuel and nitrous pressure. I recommend
you use these as a
target, maybe start a bit richer than shown.
I don't have information here on the use of a jet to apply vacuum pressure to a fuel pressure regulator,
as in the NOS 5176
kit. The use of jets for this purpose, and calling them "fuel jets" is NOT related in any way to the normal
use of fuel jets in a
wet system, and I'm not aware of algorithms that would allow you to select these jets in combination with
nitrous jets, to
create a certain amount of horsepower. Contact the nitrous kit vendor for recommendations.
A PCM scanner (Diacom, Autotap, etc) is crucial to successful tuning of your nitrous system. I run most
of my nitrous passes
while logging with an Autotap, and also use it at the dyno. You'll be monitoring the oxygen sensor
voltages, knock, etc, and
adjusting the jets to provide the best combination. Note, though, that the stock oxygen sensors are not
and a wideband O2 sensor (say, at a dyno) is much better to use if you have access to one. Typical O2
values should be
around 860-880mv (higher is richer) when running the motor normally aspirated, and I try to tune mine
to 900-940 on nitrous.
As mentioned above, you'll adjust jet sizes up or down to enrich or lean out the mixture. You'll probably
see some knock
during a shift, but should see none otherwise. You can add timing retard to reduce knock.
Doing your scanner tuning at a dyno provides another benefit, since you can see the power the engine
is generating, while
you tune the system. It also makes the whole tuning process easier than racing up and down the track,
swapping jets in the
pits, waiting in lines, etc.
HOW MUCH CAN I RUN?
On a stock V8 motor, 150hp appears to be the limit. 125hp is probably a "safe" setup, assuming it's
working well. A built,
forged motor can take quite a bit more, 200-250hp is probably reasonable, but you'll be going to direct
port if you want more
power. On a six-cylinder motor, 75-100hp, while stock 4 cylinder can take from 35-75hp. These seem to
be the highest "safe"
setups. Of course, I use the term "safe" very loosely here, to mean that folks have run this amount of
nitrous for quite a
while without blowing up their engines.
Most nitrous systems are build with a purge feature. The purpose of a purge is to get liquid nitrous oxide
up to the front of
the car, filling the hoses with nitrous rather than air. To do this, another solenoid is used, but rather than
nitrous into the motor, it's usually shot up over the hood, or out of the grill so you can purge until it
creates a nice fog. It also
looks real cool.. Of course, no fuel is used during a purge.
It's virtually mandatory that you install your nitrous system with a bottle heater, which is used to raise up
the temperature of
the bottle, and therefore increase the pressure at which the nitrous is delivered. If you don't use one,
your pressure will
quickly drop and won't supply the volume of nitrous your vehicle was tuned for.
REMOTE BOTTLE OPENER
Normally, your nitrous bottle should be kept closed, with no pressure in the nitrous lines. But when
you're lined up against
that guy that just looks a bit too fast, you'd hate to say "excuse me, do you mind if I hop out and open
my bottle in the
trunk?". Easy solution, get a remote bottle opener! Most vendors have such a device, which allows you
to open the bottle
electrically via a switch on your dash.
You can break tons of other parts on your car by running nitrous, or any other large power addition.
Running slicks at the
track will just accelerate the damage. Here are a few things to keep in mind.
The huge torque spike at low rpm's is particularly hard on clutches. I had to buy a new clutch as soon as
I made my first pass
with nitrous on slicks. Keep in mind, on a manual transmission car, you're likely to need one too.
Not unique to nitrous, but certainly a common failure on high horsepower cars, is the rear end. A 4th
generation f-body, with
a stock 10-bolt rear end, is not going to last long on nitrous. Plan for an expensive (~$2,000) upgrade at
With all the extra power, you'll have trouble hooking up with any traction, especially on street tires. You'll
probably have to
use drag radials at least, or slicks if you're adding any significant power.