A nitrous oxide molecule is made up of 2 atoms of nitrogen
and 1 atom of oxygen. By weight it is 36% oxygen (air is only
23.6% oxygen). At 70° F it takes 760 psi of vapor pressure
to hold nitrous in liquid form. The critical temperature is
97.7° F; at this temp the vapor pressure can no longer
hold the nitrous in liquid form. At this point the nitrous
turns gaseous and will be at 1069 psi. As temperature rises
further, so will pressure, but it will remain in gaseous form.
If you intend to siphon liquid nitrous, it is important to
keep the temperature below 97.7°. When liquid nitrous
is released, it will go from 760 psi to 14.7 psi (normal atmospheric
pressure). It will then begin to boil and rapidly expand;
the pressure drop will cause the temperature to decrease.
Nitrous boils at 129.1° below zero.
Nitrous oxide does not burn, it is an oxidizer. It provides
more oxygen, so more fuel can be burned, and the result is
more power. The atoms in a nitrous oxide molecule are bonded
together. The oxygen is not free, but fortunately the bond
breaks down as temperature rises. At 565° F, the bond
is broken and the oxygen is then free. Combustion temperatures
are much more than 565°, so it's not a problem. By adding
nitrous oxide to an engine, the total amount of oxygen is
increased and other gasses that do not support combustion
(mostly nitrogen) are decreased. This speeds the burn rate
and requires less timing advance for peak output. It is hard
from many people to grasp gaining power with less timing,
but it's a fact. Peak cylinder pressure must occur at approximately
20°ATDC to make peak power. If you speed the burn rate,
peak cylinder pressure will occur too soon. It is easy to
run too much ignition advance with nitrous, but too much will
not only hurt power, it can quickly bring a nitrous engine
into detonation and destroy it.
Nitrous Kits will increase the chance of detonation. To
keep the engine out of detonation, you must control the extra
heat that nitrous makes. The easiest way to do this is to
add more fuel. All nitrous systems come with rich jetting
to give you a safe starting point. The extra fuel takes away
heat and raises the detonation limit. Another way of controlling
heat is with water injection. A well set up water injection
system will allow you to run the chemically correct nitrous
to fuel ratio, so the system will be more fuel-efficient.
If you don't try to over do it, and keep the hp levels within
reason, running slightly richer should be all you'll need
to control detonation. Water injection and running richer
will both reduce the power output, but raising the detonation
limit will allow more nitrous to be used to get more power.
The chemically correct nitrous to gasoline ratio is 9.649:1.
If a nitrous engine runs lean, it can destroy the engine in
a matter of seconds. There must be enough fuel for the nitrous
to react with, if there isn't, temperatures rise rapidly.
The oxygen that couldn't react with fuel will oxidize any
parts that get hot enough. So don't run lean.
The most common systems are the spray bar type. A plate gets
sandwiched between the carb and manifold. There are two spray
bars in each plate, the upper one is nitrous oxide and the
lower one is fuel. The nitrous sprays over the fuel to give
a better nitrous fuel mixture. Plates are easy to install
and provide good performance, but they are not the best. The
nitrous must travel through the entire intake manifold. The
longer it takes to get to the cylinders, the more it expands.
The more room that nitrous occupies, the less of the normally
aspirated mixture the engine will get. So the engine will
make more power if the point of injection is as close to the
cylinders as possible. Another problem with spray bars is
when using larger kits; the motor will hesitate slightly when
the nitrous is activated. When the nitrous first travels down
the spray bar, it hits the dead end of the bar and sends a
pulse backwards, which impedes flow. Once the system is running
there are no problems, but that slight hesitation could cause
tire spin. This reversion is mostly a problem on larger kits,
around 300 hp or so.
Also known as foggers (started by NOS Systems), the nozzle
nitrous systems can produce much more power without any reversion
problems. With this type of system, you must drill and tap
each intake runner near the cylinder head and run at least
1 nozzle for each cylinder (many multiple stage systems will
run more than 1 nozzle per cylinder). There is much more plumbing
in a nozzle system, but they give better mixture (or fog),
because the nitrous and fuel mix before they are injected.
The high pressure nitrous breaks the fuel into a very fine
mist. The point of injection can be very close to the cylinder
for minimal expansion. In many cases, depending on how the
nozzles are situated and aimed, the normally aspirated airflow
will increase. So there are many advantages to the nozzle
Cooler intake air is denser and contain more oxygen atoms
per cubic foot. So cooler air will allow more fuel to be burned
and intern make more power. A 10 degree drop in temperature
can add 1 to 1.5% power to an engine. Nitrous oxide boils
at -129°F and it will begin to boil as soon as it is injected.
This can cause a 80° or so drop in manifold air temperature.
Now if we are dealing with say a 400 hp engine, we can see
well over 30 hp gained from the cooling effect alone. This
cooling effect also helps the engine deal with detonation.
If you were to build a 550 hp 350 Chevy, it would have to
rev to 7000+ rpm to make that kind of power and only make
power in a narrow rpm range. A nitrous injected 350 Chevy
making 550 hp would make that power at a much lower rpm and
higher average horsepower. So the nitrous engine will out
perform the normally aspirated engine by a healthy margin.
The reason is that nitrous flow remains constant no matter
what rpm the engine is at. At lower speeds there is more time
for the nitrous to fill the cylinders, so you get more nitrous
in the cylinders per power stroke at lower rpm. This will
boost power more at low rpm (before the engine is in it's
power band). As rpm increases, and gets in the power band
of the engine, you will get less nitrous per power stroke,
but the engine will start making more normally aspirated power.
This really flattens out the torque curve and widens the power
So Why Not Pure Oxygen?
Air has only 23.6% oxygen by weight, the rest is made up largely
of nitrogen. That nitrogen does not aid in combustion at all,
but it does absorb and carry heat away. When you add nitrous,
it has 36% oxygen with the rest being nitrogen. So the more
nitrous oxide you add, the less percentage of nitrogen is
available to absorb heat. That is why nitrous increases engine
heat very rapidly. If we were to add pure oxygen (which has
been tried), the percentage of nitrogen would fall much faster
as more oxygen was added. We would not be able to add much
oxygen before heat was a problem to control. Also compressed
oxygen is in a gaseous form, so adding oxygen takes up more
room and reduces normally aspirated power, and the amount
of nitrogen from it. By injecting liquid nitrous, the normally
aspirated power only drops slightly and it is adding oxygen
and nitrogen. To put in simply, with nitrous oxide, we can
get more oxygen atoms in the engine and have a lot more nitrogen
as well. Nitrous can make much more power before heat is uncontrollable.
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