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 figher 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 used it?
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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 your engine.
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.