What is Nitrous Oxide?
Nitrous oxide (N2O) is a compound that contains one oxygen atom and two nitrogen atoms. Nitrous oxide as a gas is colorless and odorless and has 36 percent more oxygen by weight than air. The English scientist, Joseph Priestly, first identified nitrous oxide in 1772.
One of the main factors that determine how much power an engine can produce is how much oxygen it can draw in during the induction cycle. There are several ways to pack more oxygen into the cylinder: add a supercharger or a larger camshaft, improve flow of the cylinder heads, or add nitrous oxide. Nitrous oxide is often the easiest method of adding power to your engine.
Nitrous oxide was most probably used for the first time in combustion engines after World War I but was used extensively in piston-driven aircraft by both the Allies and the Axis in World War II.
Nitrous oxide, when compressed to 600 psi at room temperature, becomes a liquid. As nitrous is introduced into the intake tract, the pressure drops and the liquid boils to a gas. When the liquid nitrous changes to a gas, it drops to approximately -129 degrees Fahrenheit.
Performance nitrous systems keep the nitrous in a liquid state until it is near the intake manifold and then inject the gas so that the nitrous is as cold as possible inside the engine. This "supercools" the intake charge. A cooler intake charge packs more air into the cylinder, which also increases power. In general, you will see a 1 percent power gain for every 10-degree drop in inlet air temperature. This is a power gain even before the nitrous gets into the cylinder!
If oxygen is what we are after, why not inject pure oxygen into the cylinder instead of nitrous? Injecting pure oxygen would create such violent, uncontrolled combustion that even small amounts could be catastrophic. With nitrous oxide, the heat of the combustion breaks the chemical bond that holds the two nitrogen atoms and the oxygen atom together. Without heat, the three atoms would remain bonded, and consequently, the oxygen atom would be unavailable to play its role in the combustion process. This is why inhaling nitrous is dangerous, leading to fatal asphyxiation, even though it has a higher oxygen content than air: Your body cannot produce the heat necessary (approximately 565 degrees Fahrenheit) to break the bond between the nitrogen and the oxygen, leaving the oxygen unavailable for respiration. Since the ignition process must start before the oxygen from the nitrous can be released, the net affect is a more controlled release of oxygen and a stable combustion process.
The optimal air/fuel ratio for complete combustion of gasoline is 14.7:1 (commonly referred to as the stoichiometric ratio). However, gasoline engines produce the best power at an air/fuel ratio of 12.5:1-13:1. Because nitrous is more oxygen-rich than air, the chemically correct air/fuel ratio becomes 9.65 parts of nitrous to 1 part of fuel (9.65:1). Additional fuel beyond 9.65:1 should be added to make maximum power and to prevent detonation (an air/fuel ratio of 8.0:1-8.2:1).
That means when oxygen-rich nitrous is introduced to an engine, additional fuel must also be supplied in order to maintain the correct air/fuel ratio. Without the additional fuel the mixture would become dangerously lean-circumstances that will almost always lead to severe and expensive engine damage.
Nitrous is stored in a bottle, which should be mounted in the trunk area or somewhere out of the driver's compartment. It is then transferred to the engine compartment via a stainless braided high-pressure line to the engine compartment.
Carbureted V-8 applications most frequently use a plate mounted under the carburetor, which has a spray bar that delivers the additional fuel and the nitrous oxide. A typical plate system uses a pair of 12-volt solenoids to control the release of the additional fuel and the nitrous oxide. The nitrous is plumbed directly to the nitrous solenoid. Fuel is supplied from the fuel supply feed line. Changeable jets control the amount of fuel and nitrous oxide fed to the spray bar.
The electric solenoids can be wired to a momentary push button in the interior of the car. An arming switch controls the power to the system so that it cannot be accidentally activated, as well as a full-throttle switch at the carburetor or throttle position switch.
Nitrous oxide is stored in the bottle under high pressure. A full 10-pound bottle will have approximately 800 to 900 psi at room temperature. At this pressure the nitrous oxide is stored as a liquid. Nitrous bottles must always be mounted at an angle with the outlet facing forward and down. This allows the siphon tube to pick up the liquid from the bottom of the bottle.
Producing more power requires a stronger engine. This is especially true when considering engines injected with nitrous oxide. If your engine is in need of repair, then adding nitrous will not help; in fact, it can make things worse.
Nitrous oxide injection has the capability to produce sudden power with increased combustion pressures and temperatures. This necessitates the addition or improvement of the engine and its support systems. How much nitrous oxide you can add depends on what type of engine you have. If you have a stock V-8 engine and a stock fuel system, you should limit your power increase to a 125hp kit.
Obviously, it's wise to be realistic when considering the amount of power an engine, transmission, and driveline can handle. A strong engine coupled to a weak transmission or differential will obviously deliver a lot of disappointment sooner or later. Even if the engine is equipped with the best ignition and fuel systems, its internal components have to be capable of coping with the increased loadings associated with producing more power. Adding a 300hp nitrous oxide kit to a production small-block Chevrolet will not last long. It's better to be a little conservative and gain greater reliability and longer component life.
One of the most important considerations when using nitrous oxide is the selection of a top-notch fuel system. A lack of fuel is the quickest way to damage a nitrous-injected engine. Starved of the necessary fuel, combustion temperatures will soar. Extreme temperatures cause catastrophic damage to pistons and other parts in the combustion chamber and lead to massive engine failures.
To prevent this, the fuel system must be able to handle both the normal engine requirements as well as the additional demands created by the nitrous system. You must immediately upgrade the fuel system if there's the slightest hint that the fuel supply is insufficient.
There are two options available to remedy the situation. One solution is to beef-up the existing fuel system. The preferred method, though, is to have two independent fuel systems: one that serves the engine and another dedicated solely to the supply of fuel for the nitrous system. This is ideal because it protects the engine from spikes in pressure-an undesirable characteristic that can occur when using nitrous oxide. Additionally, this will allow you to make the flow test of the fuel system easier.
Note that the fuel supply (pressure and volume) must be checked at wide-open throttle, since you may have plenty of fuel pressure at idle, but at speed, with the button pushed, pressure could drop dramatically. (Remember, fuel pressure and volume are NOT the same!)
Light the Fire
Increased combustion pressures often require a more powerful ignition system than that on a non-nitrous engine. This is especially true on kits for late-model, fuel-injected production cars. Since many ignition systems are only powerful enough to operate under the conditions they were designed for, increased combustion pressures may exceed the limits of the original ignition system. A lack of spark can cause drastic reductions in power and allows the unburned, highly atomized air/fuel mixture to enter the exhaust system, which can lead to explosive backfires.
Timing also plays a key role in the performance of a nitrous kit. Due to the increased cylinder pressures, it's unnecessary and inadvisable to advance the timing as much as a normally aspirated engine. Overly advanced timing leads to detonation and can cause severe damage to the engine's internals. As with jetting, start conservatively and gradually progress to optimum performance. The following adjustments will serve as a general rule of thumb:
After the kit is installed and plumbed, but before the bottle is installed, the first step is to check the operation of the solenoids. Arm the system and press the button. An audible click should be heard from both solenoids.
Next, run the vehicle and check for fuel leaks. Now, with the fuel system pressurized and the car idling, raise the engine speed, arm the system, and tap the button momentarily. The engine speed should drop as soon as the button is pushed, indicating the extra the fuel was injected.
Now install the bottle. With the engine off, open the bottle valve and check for leaks. If there are no leaks, you are now set to go to the drag strip to try your system.
It is best to initially activate your nitrous system at wide-open throttle (WOT). Using nitrous at too low of an engine speed can cause detonation, so it is best to be careful. Never activate the nitrous system with the engine not running. If you do, an explosive backfire could occur on start up. If you accidentally activate the system with the engine off, pull the coil wire off or disconnect the power to the coil, and crank the engine over for 30 seconds to clear the nitrous from the cylinders.
As previously stated, nitrous oxide is stored as a liquid under high pressure in the bottle. Bottle pressure will vary with temperature. If heat were continually applied to the bottle without a safety release, the bottle would explode. The explosion would be so violent that it could destroy the car that the bottle was mounted in. While each bottle is equipped with a 3,000-psi pressure relief to prevent explosions, care should be taken not to allow the bottle to be overheated.
The fitting on the valve in the upright position is the pressure relief. Should the cylinder exceed 3,000 psi, this relief fitting is where the cylinder will empty. If the car is to be used in IHRA competition, the rules dictate this relief fitting be vented to the outside of the car, a good idea in any situation. Relief valves with a threaded housing that accepts an -8 AN hose end are available.
Bottle pressure is also a key to nitrous system performance. Nitrous kits are usually jetted for optimal performance at a bottle pressure of between 950 and 1,000 psi. If the bottle pressure is higher, the mixture could be too lean, and if the bottle pressure is lower, the mixture is too rich. This is why nitrous racers are always concerned about bottle pressure.
Fuel-injected cars are often easier to install a nitrous oxide system on than cars with carburetors, and they respond just as well. The fuel supply is often as close as the injector fuel rail. A plate can be installed immediately after the throttle body, or a nozzle can be installed in the air duct up stream.
The most common nitrous systems consist of a single stage. Duplicating the single-stage hardware to make two or more stages can allow the added power to be controlled. Adding 300 hp of nitrous in a single stage is likely to just boil the tires when the button is pushed, unless the chassis is very robust. Two 150hp stages can allow the tires and chassis to recover from the first hit before the second stage is activated. This type of progressive electronic control system is what the fastest nitrous racers use.
Whether you have a simple plate system or a multi-stage individual runner system with nozzles, very few power modifications have the kick that nitrous oxide provides. A properly installed, safely operated nitrous system may offer the best bang for the buck of any power adder. If you have never felt the power of nitrous, catch a ride in a friend's car, but be forewarned, the nitrous rush can be addictive
Top Ten Nitrous Mistakes
1.Never heat a nitrous bottle with anything but an approved bottle heater. If you heat a nitrous bottle too quickly, an explosion could occur. Heating a bottle with a torch can result in a weak spot on the cylinder that may fail, explosively.
2.Never attach the power supply for a 12-volt bottle heater directly to the battery. Always use a 12-volt supply that is hot only when the ignition is on, so that the system is fail-safe.
3.Never allow liquid nitrous to touch your skin. Liquid nitrous at approximately -125 degrees Fahrenheit will freeze your skin instantly and could cause permanent damage.
4.Never inhale nitrous oxide. Inhaling nitrous in large enough doses can be fatal.
5.Never leave the nitrous bottle valve open for extended periods of time. Leaving the bottle valve open could damage the seals in the nitrous solenoids.
6.Do not exceed a nitrous bottle pressure of 1,100 psi. The nitrous system was designed to run at 1,000 psi, and a high pressure will lean out the nitrous-to-fuel mixture and could cause severe engine damage. Higher pressures may adversely affect the seals in the nitrous solenoids.
7.Never assume that your stock fuel system is sufficient to meet the fuel demands of your nitrous system and the engine. If a stock fuel system cannot supply enough fuel, the mixture will become too lean and severe engine damage will occur.
8.Never assume that idle fuel pressure and wide-open throttle fuel pressure are the same. Always check fuel pressure at wide-open throttle under load.
9.Never use Teflon tape on any pipe thread in a nitrous system, since loose pieces of tape could clog the solenoids or jets. Always use Teflon paste.
10.Never operate the nitrous system without the engine running. An explosion could occur upon start up.