Single Point Injection

We discussed previously about how nitrous oxide works and the affects it can have on your engine if abused. Now let's examine the single point injection system. These are the most common and simple applications of nitrous oxide, so we will start with them.
Dry single point nitrous injection systems have a single nozzle and one nitrous solenoid. They are also called single fogger systems. In this type of nitrous oxide set up, the nitrous is introduced to the engine from the solenoid through the single nozzle. These simple set ups will require additional fuel to keep the air fuel ratio at optimum levels. This can be accomplished by adding a fuel pressure regulator that increases fuel pressure to the injectors when the nitrous solenoid is activated.


A typical single point injection system can come it two varieties: wet or dry injection. The dry injection systems supply only the nitrous oxide to the system. Wet injection systems mix the nitrous with fuel before delivering it to the engine. The dry injection system may contain a solenoid, the nitrous jets, and the nitrous pressure reference fuel pressure regulator. To get the added extra fuel, these systems will clamp the return fuel lines under nitrous conditions, raising the fuel pressure at the injectors. This will provide the extra fuel needed to stay at the optimum mixture levels. The disadvantage of these systems is that you can only squeeze so much fuel out of the stock injectors and fuel pump, and as the fuel ratio leans out under heavy nitrous runs, you get an increased risk of premature detonation which, when coupled with nitrous oxide, can have some terrible results.


Wet single point injection systems use a fogging or "fogger" nozzle to mix the fuel and nitrous together before spraying it into the intake. These systems solve the problem of the dry single point systems not being able to provide enough fuel. Considering that modern intakes are designed to flow air and not liquid, it is important to mix the fuel and nitrous gas before the intake throttle body. Most tuners and mechanics suggest at least six inches before the throttle body to get a good mixture. Since this type of fogging system has its own fuel supply, it is not limited to the fuel pump's output.


Which one is better? That depends on how much nitrous oxide you intend to run through the system. Dry point injection is typically good for up to 50 horsepower shots because of the even fuel distribution from the injectors. A shot larger than this and you risk running lean, so the additional fuel is needed from a wet injection system. It is also a good idea to run a cooler grade spark plugs and at least 91 octane gas for these applications. Above 50 horsepower shots, and you may need to retard the timing by 2-4 degrees.


If you intend to blow the doors off the competition with a 75 shot or more of nitrous oxide, look into a direct port injection system. These nitrous oxide injection systems will be used specifically for race applications, and are not recommended for street use. These types of systems will be looked at in greater detail in our next segment.


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Nitrous Oxide Injection Systems

To understand how nitrous oxide injection impacts and engine, let's examine how an engine works. An engine creates power by transfering energy created by fuel combustion. Combustion is a form of rapid oxidation, which requires oxygen as the name dictates. The amount of oxygen determines how much fuel can be burned, and the more fuel that is burned, the more power is created.

Nitrous Oxide is a chemical that is rich in Nitrogen and Oxygen. Injecting nitrous oxide increases the oxygen density of the intake air. Nitrogen is a cryogenic liquid with a very high vapor pressure. It must be kept at a minimum of 745 psi to remain a liquid at room temperature.

Since the vapor pressure is so high as a liquid at room temperature, when nitrous oxide is released into the atmosphere, there is a very rapid expansion as it metamorphoses from a liquid to a gas. There is a large amount of evaporative cooling that takes place as the liquid evaporates, drastically reducing the temperature of the surrounding air.

When this chemical reaction is added to the intake air of a combustion engine, you get a double effect of an oxygen rich intake charge and supercooled, dense air. The higher air density and oxygen percentages allow for more fuel to burn, creating large amounts of power. This cooler air lowers the chances of premature detonation which can be damaging to internal engine components. Just the cooler air alone can increase horsepower by about 5 percent.

As stated earlier, you must have extra fuel for the combustion to occur properly because with an oxygen rich and dense intake charge, you will find yourself running dangerously lean under the conditions of nitrous oxide injection. To obtain more fuel, there are several tricks that can be done.

First, you can add an aftermarket fuel pressure regulator for nitrous systems. These regulators will clamp the return fuel line under nitrous injection, raising the fuel pressure to the injectors which will provide more fuel. Others have added a fuel cell which is a small additional "tank" of fuel, usually filled with race or higher octane fuel, that will engage and supplement the factory fuel settings to kep the air/fuel ratio in the optimum zone for the maximum amount of power.

You can't just squeeze every ounce of power out of your engine without some faily major modifications to its internals though. On a standard engine with no modifications, it is recommended to stay within a maximum of 40% of the rated horsepower of your vehicleon the amount of horsepower shots, and keep the shots to less than 10 seconds per shot. More than this on a standard motor and you could get yourself in big trouble. I know of several istances where more than the recommended horsepower shot was used, only at the sacrifice of blown rings or a blown off intake manifold.

There are several types of systems which will be covered int he next few posts, such as mild street setups, dry single point injection, wet single point injection, direct port injection, and two stage race applications.

Hopefully this has helped you better understand how nitrous oxide injection works, so we can focus on the actual systems in the future.