Nitrous Oxide
by Stephen Scott

People are always saying that I'm crazy to put nitrous on my truck. They say it will destroy my engine. I've done some research and found this article. Reprinted without permission.

Nitrous oxide injection has become one of the most popular methods of increasing the power output of an internal combustion engine, and justifiably so. Nitrous oxide (N2O) injection is simple precisely metered N2O and gasoline are force-fed into the engine, supplementing the normal air/fuel mixture to release more work-producing heat during the combustion process. The only equipment required is an N2O storage tank, a pair of solenoid-actuated valves to control the N2O and gasoline flow, nozzles (or spray bars) to distribute the N2O and gasoline, and the various hoses, lines and wiring to connect the system. Engine disassembly is not required for installation-and the system can be removed for resale or transfer to another car at any time. The cost of a new professionally prepared system is reasonable (between $400 and $600 US in most cases), and the power increase is dramatic (usually in excess of 100 hp for most street systems).

As popular as N2O systems have become (industry estimates are that over 20,000 systems are now in use!), many enthusiasts still think of N2O as some sort of evil black magic. Honest and reliable information about the effects of nitrous oxide, the care and installation of N2O systems and tuning tips regarding N2O use has been practically nonexistent. Instead, the bench racers pass along inflated rumors of unbelievable power gains that rival a Saturn rocket, and incredible horror stories of vehicles supposedly erupting in fireballs that would make a hydrogen bomb seem small. To set the record straight, we've solicited the help of the folks at Nitrous Oxide Systems (2420 Gundry Ave., Long Beach, CA 90806) to answer the most commonly asked technical questions and put some misconceptions about N2O to rest.

FALLACY: N2O is explosive and a fire hazard.
FACT: N2O will not burn, nor is it a fuel. It is merely an oxygen-rich compound that supports the combustion of additional fuel. That's why additional fuel is injected along with the N2O on all N2O systems. It is true that if N2O is added to a combustion process already in progress, the extra oxygen may cause rapid, uncontrolled combustion, thus raising the peak temperatures produced.

FALLACY: An N2O system will add 200 hp to a car.
FACT: Although it is possible for the average N2O street system to add 150 + hp to an engine under ideal conditions, most street systems realistically add 90 to 125 hp to the average engine, but the effect of another 100 hp to most late model stockers is so dramatic that you'd be easily misled into thinking the power gain had been far greater. The power increase also varies with N2O tank pressure, fuel pressure, engine displacement, engine speed, ignition timing, the normal air/fuel mixture and the N2O system design, so it is impossible to accurately predict the actual power gain any car might display. As a good rule of thumb, figure on 110-120 hp, regardless of the advertising claims. There are special competition N2O systems that typically add another 50-75 hp over what the street system produces, but forged pistons, special rings, and many other specialized pieces are recommended to withstand the extra cylinder pressure when these high-output systems are employed. Without the heavy-duty modification, engine damage would be likely.

FALLACY: N2O adds octane to the fuel being used and reduces detonation.
FACT: N2O does not increase the octane of the fuel being used. However, nitrous oxide injection may suppress detonation due to the intercooling effect of the depressurizing of the compressed N2O and by the introduction of extra gasoline. Most N2O systems intentionally add about 10 percent excess fuel as a safeguard against accidentally leaning the mixture. The extra fuel acts almost like water injection to cool the mixture and dampen detonation.

FALLACY: Premium fuel must be used with N2O injection.
FACT: The purpose of N2O injection is to support the combustion of extra fuel, thereby releasing more work-producing heat in the combustion chambers. Consequently, maximum cylinder pressures with N2O will be higher than when it isn't in use. Extra cylinder pressure does tend to cause preignition and uncontrolled combustion, but as previously described, N2O injection also tends to suppress detonation. With most street N2O systems, these two opposing forces tend to cancel each other out, which means you can continue to use the same octane gas that was acceptable before the N2O was added. Because competition N2O systems inject a greater quantity of N2O and gasoline than do street N2O systems, cylinder pressure is frequently raised to the point where a higher octane fuel (or anti-detonation additives) must be used.

FALLACY: N2O will melt pistons, rings and valves.
FACT: If the N2O system has been properly designed to supply the correct amount of gasoline along with the N2O, combustion temperatures will actually be lower than when N2O isn't being used, so damage from elevated temperatures does not occur. Since the purpose of N2O injection is to make more heat, this may sound like a contradiction, but it isn't. With N2O, the total amount of heat energy released is greater, but the peak combustion temperature is lower. Think of it this way: A huge oil storage tank burning at an average temperature of 1000 degrees releases a lot more energy than a small acetylene torch with a tip temperature of 2000 degrees. That's a comparison by extremes, but in an engine with N2O injection, each cylinder might be burning 25 percent more fuel at a temperature of 1400 degrees than the engine would without N2O at 1460 degrees.
Claims of engine damage while using N2O are not totally fictitious, however, since if cylinder pressure does rise above the octane tolerance of the fuel being used, detonation occurs, and that will damage pistons, rings, etc.

FALLACY: Using N2O on an engine imposes no special maintenance problems.
FACT: Because N2O injection does increase effective cylinder pressure, normal blow-by past the piston rings is increased, thereby increasing oil contamination. Consequently, oil drain and filter replacement intervals should be decreased by roughly 25 to 33 percent. Additionally, N2O systems use filters in both the N2O line and the gasoline line just ahead of the solenoid valves. These filters should be checked for any restriction with every 100 pounds of N2O used. Restricted filters can upset the balance of nitrous oxide to gasoline, which could cause a problem. If the N2O filter becomes restricted, the mixture will go rich, causing the car to "lay down" or run sluggishly. If the fuel filter becomes restricted, the mixture will lean out. The first indication of this is usually a popping back through the carburetor in high gear. Such popping back is a warning that you'd better get the mixture straightened out before serious damage occurs.

FALLACY: Freezing the N2O tank increases N2O flow and the power output.
FACT: Whenever a pressure vessel is cooled, internal pressure drops. Most N2O systems are designed to work with tank pressures of 600-800 psi, which is the approximate pressure of a normal bottle at room temperature (approximately 72 degrees). If the bottle is cooled below room temperature, the pressure quickly falls, and flow would be reduced to the nozzles. For example, a bottle that had 800 psi at 75 degrees would fall to 450 psi at 30 degrees, and only 275 psi at O degrees.
On the other side of the coin, heating the bottle increases the pressure, but heat also tends to make the N2O vaporize in the line between the solenoid valve and the discharge nozzle, which upsets metering and reduces N2O flow. Ideally, the bottle and lines should be kept at room temperature. At the drags, some cooling of the bottle may be required to achieve this while the car sits in the staging lanes, but a damp cloth or towel wrapped around the bottle will generally be all that's required. If you really want to pursue additional cooling, chill the line between the solenoid
valve and the nozzle, and keep that line as short as possible to reduce the likelihood of vaporization before the discharge nozzles.

FALLACY: N2O injection in the individual manifold runners, as close as possible to the cylinder head, is more effective than injection immediately below the carburetor.
FACT: Although it used to be thought that direct port injection improved performance by assuring equal distribution, subsequent vehicle and dyno tests have shown that under-the-carb injection seems to provide a greater power increase since the gasoline has more time to vaporize as it travels down the intake runners. Of course, for under the carb injection to work properly, the nozzles, or spray bar, must be designed to provide even distribution to every manifold runner.

FALLACY: As long as there's still pressure in the N2O bottle, some N2O is left and the system will function properly.
FACT: An N2O system meters and discharges liquid N2O when everything is working properly. When filled, an N2O bottle is only 68 percent full of liquid. The remaining space is specified as an expansion area. Additionally, an N2O tank needs a siphon tube to assure that the pressure head in the expansion area forces liquid N2O out into the lines, rather than gaseous N2O. When the liquid N2O is expended, it is not uncommon for the tank to still have 600 psi pressure, so pressure alone is not an indicator of N2O. Gaseous N2O is clear, whereas liquid N2O, vaporizing as it leaves the nozzle, will be white in color. This is a more accurate indication of whether there is still liquid N2O in the bottle.

FALLACY: You need a prescription to buy N2O.
FACT: A prescription is not required to buy industrial grade nitrous oxide for automotive use. Nitrous oxide is available at most compressed gas suppliers, such as welding gas supply houses, but we have heard of isolated cases where a particular dealer who doesn't want to be bothered servicing hot rodders will use the excuse that you must have a prescription. If medical grade N2O (the only difference is the sterilization of the bottles) was being sought, then a prescription would be required. To make the purchase of N2O even easier, many speed shops are now refilling N2O bottles. If you live in a really isolated area or are confronted by an uncooperative dealer, the N2O system manufacturers will refill your tank, but of course, shipping the bottle back and forth is an inconvenience.

FALLACY: N2O requires no special tuning adjustments.
FACT: Force feeding N2O and extra fuel into the combustion chambers increases the density of the mixture, which increases the burning rate of the mixture. Consequently, it is frequently necessary to retard the ignition timing slightly for optimum results. The greater charge density also imposes a heavier load on the ignition system, so a good high-energy ignition system, with good spark plug wires and clean spark plugs is essential. If a competition N2O system is being used, the plug gap should be limited to a maximum of .035-inch, and plugs one or two heat ranges colder than stock are recommended to help dissipate the extra heat of combustion.

FALLACY: You can build your own N2O system.
FACT: If you're sharp enough, you could. But if you don't properly size the discharge nozzles, or you select the wrong kind of solenoid valves, or don't get the N2O distribution even to all cylinders, the trial and error testing process may include rebuilding a few engines. It's probably cheaper to buy a professionally prepared system in the long run.

FALLACY: If tank pressure exceeds 850 psi, the solenoid valves will leak, flooding the manifold with N2O.
FACT: The solenoid valves used on some systems are rated at 850 psi working pressure. Other systems have solenoids with even higher ratings. In truth, the ratings are conservative and even the lowest rated solenoids being used will work at pressures up to 1500 psi. The working pressure has nothing to do with the pressure at which the solenoid will leak, since pressure actually helps close the valve, so the higher the pressure, the more tightly it seals. The working pressure or rating only refers to the solenoid's ability to open the valve against the pressure in the system.

FALLACY: N2O will blow up your engine.
FACT: If the N2O solenoid valve leaks or malfunctions while the engine is off, the manifold can become charged with a very lean mixture of N2O and gasoline. When the ignition is first turned on, a spark impulse may occur in a cylinder where the intake valve is standing open, igniting the mixture, which will virtually explode. Carburetors have been blown off manifolds in such situations. Consequently, it is advisable to turn off the main valve on the N2O tank whenever the car is going to be parked for several hours. If a leak is ever suspected, simply remove the coil wire and crank the engine for about 10 seconds to clear any N2O contamination.

FALLACY: You can smell leaking N2O.
FACT: Nitrous oxide is an odorless, colorless gas. However automotive NOS has a sulfur smell to prevent misuse.

FALLACY: There's no limit to how much power you can make with N2O.
FACT: More N2O and more fuel equates to more power, but there's a definite limit to how much any engine will stand. It all comes down to: How fast do you want t
o go? And at what price?