The power potential of nitrous oxide was thrust into the spotlight during World War II when German Messerschmitt fighters would suddenly accelerate away from pursuing Allied aircraft, sometimes leaving a puff of smoke in their wake. The planes had a hot button that would supply a short burst of nitrous-generated speed. It would take some time for this technology to trickle into the automotive scene. The trial-and-error evolution of nitrous oxide in the '60s and '70s gave many the perception that nitrous was a volatile means of producing power. In the 1990s computer controls became an integral part of nitrous systems and this volatile aura began to fade. Today, nitrous oxide is a safe power adder as long as the system is jetted to realistic power levels, there is enough fuel supply on-hand and the system is installed properly. So don't expect to pump 300-hp worth of nitrous into a stock 92-hp Honda DX engine, be sure the fuel system is upgraded to match the expected power level and closely follow the supplied instructions or have an experienced shop do the wrenching.
The biggest value of nitrous is its versatility. It doesn't care what car or engine you have; hook it up right and it will make power. While there are application-specific kits offered, universal nitrous is a big answer to those who own "they don't make anything for my car" cars.
Nitrous On A Molecular Level
A power adder allows an engine to burn more fuel and burning more fuel is the only way to make more power. But to make power in an internal combustion engine there must be a proper ratio of fuel and air. It is the air portion of the equation where nitrous makes its impact felt. Nitrous oxide is a molecule with two nitrogen atoms and one oxygen atom. In the nitrous bottle and under pressure the nitrous is in liquid form. When it is released through the nozzle it turns to gas. The act of combustion breaks the chemical bond of the molecule, releasing the oxygen atom. By weight, air is 23-percent oxygen while nitrous is 36-percent oxygen. So there is more oxygen present in the nitrous-enhanced combustion chamber ready to make power. When the proper amount of fuel is introduced and sparked that's what happens--more power.
Dry Manifold,
Wet-Manifold, Direct Port
There are two basic types of nitrous systems--dry manifold and wet manifold. A dry system uses a nozzle to inject only nitrous into the intake tract. Fuel enrichment is handled via the fuel injectors by increasing fuel pressure or injector pulsewidth when the system is activated. A wet system injects fuel and nitrous through the same nozzle. In conventional set-ups the amount of fuel and nitrous injected into the engine is determined by the orifice size of the jets installed in the nozzle. The typical system is activated by a throttle-mounted Hobbs switch that fires the nitrous solenoid and releases the nitrous when the engine sees wide-open throttle.
A possible drawback with a single-nozzle system is it relies on the design of the intake manifold to distribute the nitrous or nitrous/gasoline mixture to the cylinders. By virtue of their design or casting shifts some intake manifolds do not distribute air evenly to all the cylinders and as the power levels of the nitrous system increase the small differences in flow become more critical. At best, there is less precise distribution and a tuning challenge--at worst, the chances of creating a lean condition are increased.
The answer here is a direct-port system where fuel and nitrous are injected at the ports through individual nozzles positioned at each cylinder, ensuring even distribution. If you plan to run a moderate, say a 50-75 hp shot, a conventional single nozzle (wet or dry) system will work fine. At 100 shot one should consider the flow properties of the intake tract. The direct-port system is more involved from an installation standpoint as the intake must be drilled and tapped in each runner to accommodate the nozzles. Also, the port system runs a distribution block where the nitrous is routed to each individual nozzle. This plumbing also takes time and skill to install.
For racing and extreme street cars staged nitrous is the next step up. In this configuration, the system provides a set amount of nitrous at initial activation then ups the ante when the driver hits a button. These systems are basically two systems in one as each stage has its own solenoid and nozzles. The basic idea is to provide the extra power when the car has the traction to make use of it. Throwing a 250-hp shot at a front drive off the line will only granulate rubber and stress the driveline. There are endless possibilities when it comes to configuring a staged system. The major factors include engine status (built, stock), traction characteristics of the car and intended usage (street or race).
For more precise control and linear application of nitrous-enhanced power Progressive computer control is the way to go. A computer oversees the application of nitrous. Depending on the complexity of the system, the system's computer can be programmed to flow nitrous based on throttle position or over time. Throttle position progressive systems use TPS voltage to calculate when to start the flow. So at, say 2.5 volts, the nitrous begins to flow as voltage increases so does the flow until WOT where the full capability of the nitrous system is unleashed. Time-based progressive nitrous control allows the user to select the percentage of initial flow and program the amount of time it will take for the system to reach 100 percent flow. The range is 0-10 seconds. So 30 percent can be selected as the initial flow and the system can be programmed to attain 100 percent at 4 seconds.
A more advanced time-based set-up allows the user to really micro-manage the flow of nitrous. This system allows the user to program the percentage of nitrous introduced and when said percentage is introduced and increased. For example, in this scenario 25-percent of the system's capability can be brought on-line at 0 seconds, 50 percent at 3.5 seconds, 80-percent at 5.6 seconds and 100 percent at 6.9 seconds.
There are also spool-up kits for turbocharged engines. This type of system is designed to provide a moderate amount of nitrous until a pre-determined boost level is attained. The nitrous adds power but more importantly adds to the amount of exhaust gases which gets the turbo up to speed quicker. When at the specified boost the nitrous kit hands the baton of power over to the turbo system.
Engine Upgrades
For the basic 40- to 60-hp dry system no engine mods are needed. It would be wise to run premium 92-octane fuel and reduce the gap of the plugs. The fuel system should be checked to ensure it is in good working order. For some engines a colder plug may pay dividends.
As the power potential of the system goes up so does the need for engine improvements. More power is generated by burning more fuel; nitrous provides the extra oxygen need to "release" the power. So as the power increases somewhere down the line the fuel system will have to be upgraded.
A byproduct of nitrous oxide is increased cylinder pressures which is why the plug gap should be closed in basic kits. As power goes up so does the internal cylinder pressures so at some point the ignition system will need to be upgraded. The power expectations of the nitrous system and the performance of the particular stock ignition will determine when an upgrade is called for. Some nitrous systems may also require timing retard. The heat generated by nitrous can have an adverse effect on the exhaust valves and in some cases the pistons, which may need to be upgraded by way of stainless-steel valves and forged pistons. As with any performance engine, big power potential requires a built bottom end.
Installation Quick Tips
Each manufacturer has its own instructions but here are some basics that are universally applicable. The nitrous bottle should be installed in the trunk with the valve facing the front of the vehicle in a downward position with the valve outlet aimed at the floor. The bottle should also be tilted with the valve end higher off the floor. This is done to ensure the pick-up gets all the nitrous possible.
The nozzle in non direct-port applications should be placed four to six inches before the throttle body. This is done to ensure there is proper atomization of the mixture prior to its entering the combustion chamber. Some nozzles are directional designs that need to point in the same direction as the airflow into the engine.
Do not use Teflon tape in the fittings. The tape can be sheared off and blown into the solenoid where it can hinder the solenoid's operation and result in a lean condition and possibly catastrophic engine failure.
Be wary of ROM-tuning or adding performance chips to a nitrous engine. Nitrous likes retarded timing and chips or ROM tunes that advance timing can cause detonation or worse.
Nitrous works best at maximum or near maximum bottle pressure. One way to keep the pressure up is to install a bottle warmer, most manufacturers offer these as optional equipment.
Check your fuel filter and replace it if needed. Fuel sediment can hurt the performance of the solenoids and/or clog the jets in wet systems.
Purchase a tube-bending tool like the one NOS offers. It will save time, ensure proper connections and make the install look cleaner.
Finally, don't go crazy. Running the nitrous system continuously can be harmful to the engine. At the most hit the button for 10 to 15 seconds at a time.
Nitrous is a potent power producer that hits hard from a performance standpoint without putting one's wallet down for the count. It is a transparent technology--when not in use a nitrous system has no effect on the driveability of the car it's installed on. Furthermore, nitrous can be made to work on just about any engine. With the advent of computer control a properly installed and tuned system is a reliable avenue to power and performance.