Nitrous oxide can do serious damage. When important factors are overlooked, broken pistons, fires, and other expensive situations can result from its use. Accidents such as these have given nitrous oxide an undeserved reputation as being hard on motors and prone to mishap. The fact is that when nitrous is used carefully, there is very little that can go wrong and it can be a very dependable power adder.
The use of nitrous oxide can be a complicated subject and, unfortunately, many people misunderstand or just don't pay attention to all the information on the topic. In addition to leading to the problems already described, this also means that the majority of people are not getting the full power potential out of their nitrous systems. Indeed, there are very big power gains to be had by tuning the system to match your vehicle.
The idea behind maximum nitrous performance is simple. Having chosen the appropriate power level for your engine, just arrive at the right mixture of nitrous and fuel. As long as you have all the correct components in your ignition and fuel system, and you keep up with routine maintenance, you can then go through bottle after bottle without any worry of engine damage. This article will make suggestions as to what products can help you accomplish this and the right way to use them. Then, the only thing you'll be doing any damage to is the competition.
Let it be known that the nitrous system manufacturers are a good resource for any questions you might have. Nitrous Oxide Systems, Inc. (NOS) is by far the most widely trusted company of its kind. Its catalog alone is a valuable resource for information, as within it you'll find discussions covering what types of components to use as well as frequently asked technical questions. It's required reading for any nitrous user.
Due to the large array of modifications that are possible for any given type of car, nitrous manufacturers pick an easy starting point and sell kits designed for nearly stock vehicles. The preset nitrous/fuel mixture of the kit reflects this. This, along with the fact that the kits are adjusted on the safe side to begin with, means that everyone with a nitrous oxide system can benefit from altering system settings.
The different approaches to nitrous oxide injection all work equally well for the "moderate" power levels most street cars can handle. However, the ease of tuneability of these systems differs. The vast majority are "wet manifold" systems, which work by injecting a mixture of nitrous and fuel into the manifold. This type is easiest to adjust because there is only one nitrous and one fuel jet to change. On a "direct port" system, which uses a nozzle located in each intake runner to add fuel and nitrous directly into each cylinder, you have to change jets on each nozzle. When nitrous is introduced in the same way, but with fuel being added by the fuel injectors, it is a "dry manifold" system. Here the amount of fuel added by the injectors must be modified, by altering how high the fuel pressure is spiked. This is accomplished by changing the size of the jet in the by-pass tee, thus modifying the signal sent to the fuel regulator. Talk to the manufacturer about exactly how to go about this. Note that there is a limit as to how high a fuel pressure can be used before the injectors stop operating properly, and people using the stock settings for such wet systems have even experienced problems. It is for this reason that a larger fuel injector is often needed that doesn't require so high a pressure to deliver the necessary amount of fuel. More advanced dry systems are computer controlled and enrichment is achieved electronically, avoiding the high pressure injector "lockup" problem.The tuning discussed in this article will refer to the widely popular, easy to adjust wet systems, but the principles can be adapted to the other types as well.
With nitrous oxide injection, it is imperative that you have enough extra fuel being supplied to complement the additional fuel-burning potential of the nitrous. Too lean a mixture leads to detonation and disaster. Unless only a very small shot of nitrous is being used, factory fuel pumps are often insufficient. In any case, a high output pump will eliminate possible fuel starvation problems. Both in-line and in-tank types are available from many manufacturers. In some cases, a fuel pump is included in the nitrous kit.
Since clogged fuel lines and faulty fuel pumps are always a remote possibility, a fuel pressure safety switch is cheap insurance. Such a switch consists of a fuel pressure sensor wired into the nitrous system. It will not allow the nitrous system to activate if fuel pressure falls below a safe, user-defined level.
While nitrous motors do not need the fuel octane that turbo and supercharged engines require, don't use anything less than premium pump fuel. For higher output applications, increased octane levels are in order. Generally you should follow the nitrous system manufacturer's recommendations on what type of fuel to use based on the amount of power being added. Don't bother with octane booster, as even the most well known brands have been found to do practically nothing. Also, if the motor doesn't need it, too much octane will slow you down.
Incorrect nitrous installations can be hazardous. With the bottle rolling around in the back seat, a careless driver not only risks injury by flying bottles in an accident, but also inconsistent nitrous flow. Most bottles have a pickup tube within them, which must be oriented so that it is always immersed in liquid nitrous. If the liquid is pulled away from it under acceleration or cornering, you get vapor and this causes a rich condition, resulting in a loss of power. Be sure to mount the bottle with bottle brackets and the pickup tube oriented correctly.
For systems that utilize a nozzle located in the air intake, location and orientation of the nozzle must be carefully selected, aiming the stream of nitrous into the throttle body without obstruction. It is also imperative that the point of injection be located downstream of the mass airflow sensor, if a vehicle is so equipped. The nitrous/fuel mixture can damage the sensor's tiny filament quite easily. In addition, nitrous blowing through it throws off the sensor's reading. Remember, one of the reasons nitrous works so well as a bolt-on for late-model vehicles is because the computer does not know it is there.
As another word of warning, don't forget to use nitrous filters and fuel filters. You do not want a nitrous solenoid to get stuck open on you because it gets dirty or worn out. Solenoids must also be rebuilt periodically, but it takes a lot of use to wear them out.
Unless you are using a progressive system, nitrous oxide may only be used under full-throttle conditions at sufficient engine speeds, 2500 rpm being the suggested minimum. Failure to comply with this rule can result in a very damaging situation, the most awesome being the infamous nitrous backfire. This event can easily blow apart your intake system, cause cosmetic damage, and start a fire. To prevent this, install a full-throttle activation switch. This switch needs to be mounted so that some part of the throttle body mechanism contacts it at full throttle, allowing the system to operate. It's also a good idea to have an rpm-activated switch so that the system can't operate below a certain engine speed, 2500 being the minimum.
It's good practice to rid the nitrous lines of vapor, in order to avoid a rich condition and hesitation upon system activation. However, many people do this by simultaneously whacking the throttle and hitting the nitrous while in neutral. Occasionally this results in the aforementioned violent intake explosion. It is therefore in your best interest to have a purge solenoid kit, which at the simple press of a button vents nitrous into the atmosphere. The purge line should be mounted where visible, so that one can watch for when the plume of gas blows thick and stable, indicating that liquid has reached the solenoids and the system is ready to go.
Bottle pressure is a function of both the amount of nitrous remaining in the bottle and the temperature of the bottle. On a cold day you may only see 600 psi, while on an extremely hot day you could see well over 1,000 psi. Because the flow rate of the nitrous is greatly affected by pressure, it's important to run the same pressure every time. An electric bottle warmer is the solution to this. Most bottle warmers are equipped with thermostats that automatically turn the warmer on and off to keep the bottle within a certain temperature range. Unfortunately, due to their simple design, such thermostats are highly unreliable. Eliminate the thermostat and rely only on a manual switch to operate the warmer.
Generally, nitrous flows well anywhere from 800 psi up. A pressure of about 1,050 psi is a good choice because this is what the pressure will be anyway on a warm summer day, so you'll never have to cool the bottle. Install a nitrous pressure gauge on the dashboard where you can quickly reference it, and have the switch for the bottle warmer right there as well. This way, you can turn the warmer on and off and keep pressure at its optimum. Just remember to watch bottle pressure closely and not leave the warmer on while unattended.
Exhaust Gas Pyrometers
The temperature of an engine's exhaust gases is related to several factors, including the amount of power being made, the air/fuel ratio of your intake charge, and ignition timing. For our interests, higher exhaust temperatures are the result of leaner mixtures, while lower exhaust gas temperatures indicate overly rich mixtures.
By installing an exhaust gas temperature (EGT) gauge, you'll have advance warning of when you are going to do harm to your motor. The gauge should be mounted in plain view so that it can be continuously monitored, especially as you proceed down the quarter mile. You'll see the reading get higher and higher and eventually peak a ways past the finish line (due to the inherent delay in the device). While different cars can produce different readings, if you are getting more than 1,350* Fahrenheit maximum, you are most probably too lean. You shouldn't aim for a certain temperature; just use the gauge as an early warning device to when things are going to start getting a little too crazy in the combustion chamber. You'll also know for sure when the nitrous bottle is going empty, since the overly rich mixture will cause exhaust temperature to cool significantly. Also, if you have coated headers, you can make sure the exhaust doesn't get hot enough to damage the coating, though this may not necessarily be your maximum horsepower.
In order to ignite that potent intake charge, good aftermarket ignition systems along with reduced spark plug gaps are needed. A spec of 0.035 inches is a good number for spark plug gap. In addition, colder-heat-range spark plugs are normally necessary to dissipate heat from the plug, averting misfire and plug melting. Normally one or two heat ranges colder is sufficient. "Projected nose" plugs, which reach deep into the combustion chamber, also cause problems because heat can't leave them fast enough. And unfortunately, platinum plugs are not going to cut it either. Platinum is a poor conductor of both spark energy and heat, and this is exactly what you don't want.
Probably the most important thing to remember in terms of the ignition system is not to use too much timing advance. While it's true that when you advance timing, you make more power--until you get to the point of detonation--much less timing is needed to arrive at optimum power with nitrous use. Due to the much higher cylinder pressures generated by a more intense burn, nitrous motors need retarded ignition timing in order to delay the time of peak pressure, keeping cylinder pressures within reason and thus avoiding abnormal combustion.
In this case as well, it's best to follow the guidelines recommended by nitrous system manufacturers when it comes to amount of timing retard required. Often the stock setting is acceptable, but when not shooting the spray, most cars perform better with advanced timing. This doesn't mean that you need to run retarded timing all the time and lose performance when running naturally-aspirated. Companies like MSD Ignition offer a number of devices that allow you to retard timing as needed when the juice starts to flow. A retard unit will automatically retard timing by a user-defined amount whenever the system is turned on. This setup is simple and foolproof. Another device available for retarding timing is an adjustable timing control. This unit has a knob that allows you to adjust timing over a wide range from the comfort of your driver's seat. When you want to use some spray, just turn the knob back to the desired timing and off you go. The disadvantage to this approach is that you have to actually remember to twist the knob back when you are about to use the system. If you can trust yourself to remember this, you'll enjoy on-the-fly, instantaneous timing adjustments for tuning purposes and to compensate for different situations on the street (such as best fuel economy).
A related topic to ignition is an rpm limiter. Many factory limiters work by cutting fuel flow to prevent the engine from spinning faster. This is not what you want, because combining nitrous with spark without sufficient fuel spells trouble. Make sure your limiter works by cutting spark, not fuel. Almost all aftermarket units function in this way.
That's right, it's time for a trip to the local drag strip, and you may very well surprise yourself at how well you can get your system to work for you. Even if your car is only used for street operation, the track provides the only real measurement of whether changes in your system have done any good. Seat-of-the-pants feel is too subjective a judgment, but the timing lights at the drags will let the facts be known.
The car must first be tuned for maximum performance in naturally-aspirated form to provide a baseline starting point. Once this is accomplished you can begin trying out the nitrous, starting out with the jetting recommended by the manufacturer for your chosen power level. First, you'll have to experiment with launch tactics. If you can't hit the juice immediately, you'll have to plan on flicking the switch a few moments after the launch. Here, having an rpm-activated switch or time delay switch can really come in handy, as you can set it so the system does this for you, taking away a lot of human error and making for very consistent passes.
Now the tuning begins. Make a couple initial passes, noting the EGT reading after you pass the quarter-mile mark. If it isn't near 1,350*, step down to a leaner (smaller number) fuel jet. Make some more passes, always keeping an eye on EGTs, and seeing if the trap speed has increased. Trap speed is a far better indicator of performance because it is less affected by traction and user error (such as switch flicking) than elapsed time. If you achieve higher trap speed and EGTs aren't too high, go leaner still. Continue this process of re-jetting and making passes until either you don't gain anything or the EGTs get too high. At this point, put back in the next richer jet, just to be safe, and you have your best mixture.
When you get home, a spark plug check is in order. Nitrous has the characteristic of cleaning plugs to make them appear like new, so the traditional method of "reading" the plugs doesn't always work. Any evidence of melting means that you are a bit too lean or you need a higher octane fuel, or that the plug heat range is too hot. An overly dirty or fouled plug would indicate too cold a heat range, an insufficient ignition system, or some other ignition problem. After correcting any problems and using the nitrous a few more times, check the plugs again to make sure all is well. Get used to this process, because you'll be changing the spark plugs more often. Any high horsepower machine will eat up spark plugs more quickly, and nitrous can do a number on them.
On subsequent trips to the track, in addition to fine-tuning the mixture, you might try adjusting the engine speed at which you change gears. It turns out that because nitrous makes such an incredible amount of torque all over the power band, a motor on nitrous assistance does not need to be revved as high and many people have discovered that the motor will perform better if it is "lugged." Also, realize that changes in outside air temperature will affect the air/fuel mixture just like a naturally-aspirated car, so you'll probably have to run fatter jetting in colder weather.
So as you can see there is more to using nitrous oxide than simply throwing a kit on and hitting the button. When you take the time to do things right, tuning and maintaining your system, you'll enjoy safe, trouble-free operation, all while making power that is even further beyond the ordinary. Good luck and keep the shiny side up.