Nitrous oxide injection is probably one of the most
misunderstood modifications in our hobby.
Nitrous oxide is an oxygen bearing compound. Its chemical designator
is N2O, so we know each nitrous oxygen molecule has two nitrogen
atoms and one oxygen atom. Nitrous oxide is sometimes incorrectly
known as "NOS". That is an acronym for the company,
Nitrous Oxide Systems, which is the largest marketer of nitrous
oxide injections system for automotive use.
Injection of nitrous oxide into the combustion chambers of an
internal combustion engine as a way to increase power output
was discovered by the German air craft industry early in the
Second World War. Thousands of German fighter and reconassance
aircraft were equipped with the so-called "GM-1" system
which added nitrous oxide to the intake charge to compensate
for reduced air density and less oxygen high altitude. The British
Royal Air Force also used aircraft engines with performance
enhanced by nitrous oxide. Interestingly, there was no use of
nitrous oxide injection by the American military air forces
other than very limited experimental use. It is interesting
to ask oneself that, if nitrous oxide injection was so dangerous
to an engine's reliability, why would so many airplanes have
In this country during 1950s the famed stock car racer Smokey
Yunick rediscoverd nitrous oxide injection as one of his many
schemes for winning races until discovered and outlawed by NASCAR.
Neverthesless, there have been several nitrous oxide cheating
scandals in NASCAR over the years and it is probably still used
today by the slowest of backmarkers. In the late-70s/early-80s
nitrous oxide was "rediscovered" by drag racers and
Today nitrous oxide injection, like many other modifications
such as more aggressive camshafts, bigger carburetors, higher
compression ratios, more free flowing intake and exhaust systems,
can be a pracitical way to more horsepower. And..like any other
modification...perhaps even more so because it so easily lends
itself to misuse...there can be a reliabity and durability price
Nitrous oxide is a colorless, non-flammable gas. It has a slightly
sweet taste and odor. It is non-toxic and non-irritating and
when inhaled in small quantitites can produce mild hysteria
and giggling or laughter. This is were the nickname "laughing
gas" comes form. When inhaled in pure form it will cause
death by asphyxiation because at atmospheric temperatures and
pressure, the oxygen in nitrous oxide is not available to the
A property of nitrous oxide is that at about 565 degrees F.,
it breaks down into nitrogen and oxygen. When it is introduced
into the intake tract of an internal combustion engine, it is
sucked into the combustion chamber and, on the compression stroke,
when the charge air temperature reachs 565 deg., a very oxygen-rich
mixture results. If we add extra fuel during nitrous oxide injection,
the effect is like a super charger or increasing the compression
ratio of the engine. Automotive nitrous systems work like the
automotive eqivalent of a jet's "afterburner" and
is used for short duration extra bursts of power.
Nitrous oxide has this effect because it has a higher percentage
of oxygen content than does the air in the atmosphere. Nitrous
has 36% oxygen by weight and the atmosphere has 23%. Additionally,
nitrous oxide is 50% more dense than air at the same pressure.
Thus, a cubic foot of nitrous oxide contains 2.3 times as much
oxygen as a cubic foot of air. Just do a bit of math in your
head and you can see if we substitute some nitrous oxide for
some of the air going into an engine than add the appropriate
amount of additional fuel, the engine is going to put out more
Simply stated, nitrous oxide injection is very much like a supercharger
or a compression ratio increase in that, during combustion,
it can dramatically increase the dynamic cylinder pressure in
Of course, when we significantly increase the cylinder pressure
in the engine, we also increase the engine's tendancy to detonate.
This is why almost all nitrous motors require retarded spark
timing during nitrous oxide operation. The cylinder pressure
increase is also why, when misused or improperly installed,
operation with nitrous causes problems with head gasket seal
and failures of the rings or pistons. I should point out that
any number of things that put an engine into severe detonation,
such as too much boost from a supercharger, low octane fuel,
excessive compression ratio or overly lean air-fuel ratio will
also cause the same kinds of damage.
Another challenge with a nitrous oxide system is getting the
delivery of nitrous oxide and additinonal fuel at the correct
proportions. If you feed nitrous to the engine without enough
extra fuel, the lean air/nitrous to fuel mixture will make the
detonation problem even worse. Combustion temperatures will
skyrocket and catistropic failure is certain to occur. If the
proportion is such that too much fuel is delivered, the power
advantage degrades rapidly.
As you can see, nitrous oxide is like any other power increasing
modification in that, when used wisely and installed properly,
it works well. Then used foolishy or installed incorectly it
can significantly reduced the reliability/durability of your
Small doses of nitrous oxide can be used in stock engines to
gain 25-35% more power. In my opinion, any more than nitrous
than that with a stock engine compromises durability too much.
This is not only true of nitrous but any modification. Take
a stock 82 or 84 engine, up the horsepower to 300hp and do nothing
to improve durability and your engine will eventually suffer.
Once you pass the 35% power increase mark with nitrous oxide
you need to look at things like forged pistons, better connectiing
rods, better bearings, etc.
Nitrous oxide is also a great value on a dollar-per-unit-power
increase when installed and operated properly. The downside,
of course, is the fun ends quiclky. The power boost lasts as
long as the nitrous. The average bottle is a 20 pounder and
with a street V8 that might be worth 20 seconds of use.
So, nitrous oxide is not the instant-engine-failure many people
think it is. When used properly and when dispensed by a properly
designed and installed system nitrous oxide can be responsible
for some phenominal increases in power.
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