In the previous installment of this series, we discussed the function of nitrous oxide on a theoretical level. Now it's time to take a look at the hardware that is required to successfully employ nitrous as a power adder.
Most nitrous users will start with a kit, the thoroughness of which varies with manufacturer and the intended application. Let's take a look at a direct-port kit for a 4-cylinder application from Nitrous Oxide Systems that we happened to have laying around the garage.
The nitrous is stored in liquid form at a relatively high pressure (around 1000 PSI, depending on temperature) in a tank, which is more commonly referred to as a "bottle". It's constructed of high-quality aluminum, and also has a high-flow valve assembly to shut off the flow of nitrous when not in use, as well as a blow-off valve to allow the nitrous to escape if an overpressure situation occurs.
It's important to mount the bottle securely in the vehicle and to treat it with extreme care when outside the vehicle, as damage to it or the valve could cause an explosive release of pressure.
Insulating blankets or heaters are often used to keep the bottle at a consistant temperature, which in turn provides a predictable pressure.
There are other precautions that are wise to take into consideration when setting up a nitrous system. For example, the use of nitrous at low engine speeds (roughly defined as lower than halfway to redline) is not recommended, as excessive cylinder pressures and damaging backfires can occur. Additionally, it's also usually desirable to turn off the nitrous system before the shift point, or before a rev limiter is encountered (especially if said limiter is of the fuel-cutoff variety). To accomplish this, an RPM activated switch is used to control the on and off points (a device incorporating both a low and high cutoff is referred to as a "window switch").
It's also desirable to retard the timing, due to the increased cylinder pressures. This can be done via an adjustment to the PCM (or distributor, if you're old school), but a better method is to use a retard box that only pulls out timing when the nitrous system is activated. Do not depend on a vehicle's knock sensor to pull timing during the use of nitrous, for it cannot pull enough timing or do it quickly enough to save the engine if detonation occurs.
Finally, if your vehicle is equipped with the type of rev limiter that shuts off fuel at redline, it's a great idea to eliminate that system and go with an ignition-cut limiter. While it's a bad idea to hit any sort of limiter while spraying nitrous, it's especially bad to cut off part of the fuel flow (which is exactly what happens when the PCM intervenes during the operation of a wet-type system).
The above features can be incorporated via discrete modules, or an all-in-one ignition box - such as the Mallory HyFire VI shown above - can be used. Some vehicles will also benefit from the hotter spark that is provided by an aftermarket box, although modern ignition systems are indeed difficult to improve upon.
The combination of a high-quality kit, modern electronics, and the right engine and vehicle modifications provides enthusiasts with the ability to implement a nitrous system in a safe and effective manner. Obviously, the optimal set-up will vary from one vehicle to another, so we suggest doing some serious research before handing over your hard-earned money.