Challenger Nitrous Kits: to Spray or Not to Spray?

Chemically speaking (on a molecular level), nitrous oxide is two parts nitrogen and one part oxygen. From an automotive perspective, nitrous oxide – giggle juice, as it’s known on the street – helps to significantly and instantly boost both horsepower and torque when it is injected into an engine.

Stored as a liquid in a highly pressurized bottle, the nitrous undergoes an instantaneous phase change from liquid to gas upon being exposed to the atmosphere when being sprayed into the intake. This change from liquid to gas causes a massive drop in temperature (-127 F, to be precise) which produces a denser charge entering the combustion chamber. Already having extra oxygen due to the reduced inlet charge temperature, the second prong of a nitrous oxide attack comes during the compression stroke. Nitrous oxide, believe it or not, will separate into nitrogen and oxygen when subjected to a temperature of 600 F. During the compression stroke, the temperature of the inlet charge raises sufficiently that the bond holding the oxygen molecule to the nitrogen molecules breaks, leaving an extra molecule of oxygen to be used in the combustion process. Extra oxygen means extra fuel is necessary in order to keep a proper air to fuel ratio, and the resultant power stroke is generated with more force which translates to a direct increase of power and torque at the wheels. 

The amount of nitrous injected dictates how much extra power will be added. This is controlled by the size of the injecting nozzles (called jets). Common denominations start at 50 horsepower and increase by twenty-five all the way up to a maximum shot of 200 horsepower.

Nitrous oxide is similar to a supercharger or turbocharger with regard to the way it functions – it simply provides more oxygen per power stroke to be combusted. The major advantage that a nitrous kit has over a conventional power adder is cost.

Installing a supercharger or turbocharger on a Challenger will easily cost over $5000 – and this is only for the basic parts. Nitrous, on the other hand, is dirt cheap (relatively speaking). An entire nitrous system can be purchased for under $1000 and that one system can add anywhere between 50 to 200 horsepower. The only downside to giggle juice is that the party is over once the bottle is empty, and a standard 10 lb bottle is only good for roughly 4-5 parties.

Does a Hemi love nitrous? Yes. Is nitrous always safe for a Hemi? No. At a certain point, too much partying stops being fun and becomes a problem. 

A stock Challenger is capable of running nitrous without detrimental effect provided the shot used is not extravagant. Running nitrous is a lot of fun, however, the extra boost in power does come at a price. Combustion cycles while under nitrous will have higher internal pressures, which puts extra strain on the rotating assembly. For Challengers that have forged pistons, this isn’t of particular concern. However, for Challengers with hypoeutectic pistons (particularly the 6.4L), this could be problematic when pumping a larger shot.

In stock form, a 75 horsepower shot is the maximum a Challenger can safely handle before the setup needs to be scrutinized. The stock camshafts have relatively long overlap periods which means cylinder pressures will remain high for an extended period of time. Adding extra pressure via nitrous (beyond a 75 hp shot) increases the chance of a stress-related failure. Thus, for those Hemis that need more than a 75 shot, careful aftermarket tuning is highly recommended in order to achieve engine stability and longevity. If too much oxygen is present without the proper amount of fuel (a lean condition), combustion temperatures can become so hot as to actually melt metal. 

With all that said, is there reason to be afraid of nitrous? No. As long as the engine has been tuned or modified accordingly, nitrous use is fairly low risk (just like any modification, really).

Bottle: A standard nitrous bottle holds 10 lbs of nitrous. The nitrous should be pressurized between 900-950 psi in order to achieve the best result. The bottle is connected to the spray plate via a feed line and can be manually operated (to open and close it) or use an electronic solenoid (remote switch).

Bottle warmer: A bottle warmer is an electric heater for the bottle that is used in order to maintain proper bottle pressure. If pressure is low, the bottle can be heated in order to raise the pressure. Optimal pressure is 900-950 psi.

Spray/injector plate: This is a small plate that is installed in the intake track prior to the throttle body. The nitrous is fed to this plate and is sprayed out of small holes in the plate. An electronic solenoid connected to the plate starts and stops the flow of nitrous into the intake.

Jets: Similar to the jets of a carburetor, the nitrous feed line can be fitted with different size nozzles called jets. The size of the jet determines how much nitrous will flow through when the solenoid activates and thus directly relates to how much power will be made. Changing power levels is as simple as swapping out the jet in the feed line.

WOT switch: Nitrous should only be injected when the throttle is wide open. Injecting at other throttle or load settings can lead to engine damage. This switch acts as a fail-safe and will only allow nitrous injection when it senses the throttle is fully open.

Window switch: A window switch is another type of fail-safe switch that will only allow the flow of nitrous between a certain RPM band (user set). This helps to ensure nitrous is not injected at the wrong time which could lead to detonation or internal component failure. 

Purge valve: A purge valve vents the nitrous feed line to the atmosphere. The purpose of this is to ensure the line is still filled with liquid nitrogen and that no gas or air is present. If any of the latter two are present in the line, while not harmful at all to the engine, performance will stutter until liquid nitrogen is flowing again.

The major difference between a wet and a dry nitrous kit is the point at which fuel is introduced. A dry kit only has nitrous injected through the spray plate and it is up to the ECU and factory injectors to sense and provide the extra fuel needed when the nitrous enters the combustion chamber. Depending on the size of the shot being used, a new fuel pump and injectors may be necessary in order to maintain proper fuel pressure and volume. A new tune and new plugs is definitely needed to run a dry system.

A wet system, on the other hand, mixes the nitrous and fuel at the injector plate before it reaches the intake manifold. Instead of just having the one nitrous feed line on the spray plate, a wet system will have a second feed line that supplies fuel to the injector plate as well. A second solenoid controls the fuel flow and when commanded allows the fuel to mix with the nitrous prior to the manifold. This system is much easier to set up and relieves the factory fuel system of the added stress of having to manage the fuel itself. It must only be verified that the stock fuel system is capable of supplying adequate pressure to both the stock injectors and the extra feed line. While a tune is definitely recommended, it is not needed when using smaller shots of nitrous. 

Given the added fuel control complexity of a dry system, most enthusiasts opt to go with a wet system.

Is the officer going to notice the big blue bottle of nitrous you have strapped to the back seat? (most install it in the trunk of the Challenger) And if he does, are you in trouble?

Well, it all depends on what state you live in. Nitrous systems are not illegal. Rather, using nitrous on the street is illegal in many states. If residing in such a state, a nitrous system must be disconnected when driving on public roads (note this does not mean removed – just disconnected). You should check with your local law enforcement to find out exactly what nitrous laws are pertinent to your locale. 

The last aspect to consider is nitrous safety. While dangerous due to its low temperature and high pressure, you may be happy to hear that nitrous is stable, easy to store, and is not flammable. It only becomes usable for combustion at 600 F and above when the molecular bonds break. The major risk associated with nitrous is temperature. If left in the sun, the bottle can heat up enough that the pressure rises dramatically and bursts the bottle. The solution to this is to keep it out of the sun, or if not possible, use a bottle blanket that will reflect the incoming rays. Really though, the safest thing to do is to take the bottle out of the car when not in use.