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 hot rodders.
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 to pay.
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 body.
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 power.
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 the engine.
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
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.