Nitrous oxide has held the allure of hot-rodders as an easy way to increase horsepower at the touch of a button. But up until a few years ago, nitrous was only used by a select group of snowmobilers who didn't mind the risk and expense of a broken motor. For many years nitrous was not something snowmobilers considered for everyday use. That's changing with the success of the BoonDocker nitrous system.
Rocky Young of Idaho Falls, Idaho, is BoonDockers founder and owner. He has wrangled in and conquered the wild nitrous oxide gnomes that broke motors.
Young started nitrous problem solving as a rebellion to turbos and the lag that occurs when lollygagging through trees at high altitudes.
Young contacted companies that retailed nitrous oxide systems and began extracting answers.
On went the nitrous systems. Motors broke. Young became frustrated, but filled with resolve. He pushed nitrous outside conventional borders. Still, motors continued breaking and his cash outlay began wearing him down.
He started to notice that original nitrous systems were very particular to bottle temperatures, which caused varying or inconsistent fuel and nitrous mixtures. A warm pressurized nitrous bottle- those set up in an unwavering temperature environment- is more consistent in delivering nitrous. Without consistent warm bottle temps, he found too-lean or too-rich mixtures would occur.
Earlier nitrous systems injected directly into the crankcase- behind the carburetors. This, like inconsistent bottle temps, brought erratic mixtures, weird fuel/oxygen transfers up the transfer ports and strange burns. The main disadvantage to injecting directly into the cylinder is that the cylinder could overfill with nitrous. Feeding nitrous through the carbs allows the cylinder to draw in only what it needs.
Traditional nitrous systems used a fixed-size jet to deliver a specific amount of fuel. Nitrous delivery must be in exact amounts to maintain a correct balance of nitrous and fuel. Nitrous delivery varies directly with nitrous pressure, and this pressure is directly related to the temperature of the nitrous bottle.
A cold bottle produces an overly rich condition that sometimes doesn't burn until the mixture reaches the pipe. When this occurs, the rich mixture ignites and backfires into the cylinder, creating a sudden down force that often breaks parts. Too hot of a bottle leads to an overly lean condition which can quickly melt a piston.
Rather than inject directly into the crankcase, the BoonDocker system fogs nitrous into the area where the motor normally breathes, the airbox. This means nitrous enters the crankcase only when the operator tightens down on the throttle and presses the little red "Wow" button.
In addition to being more dependable than traditional systems, spraying fun juice into the airbox means quicker and crisper throttle replies (only in the sense that nitrous can now be used at any throttle setting compared to a conventional system).
How nitrous makes horsepower is simple. First, nitrous oxide is sprayed into the engine where it breaks apart under high temperature into nitrogen and oxygen molecules. In order to burn properly, this extra oxygen must be supplemented with additional fuel. This extra fuel can be delivered in many different ways, and as long as the extra oxygen and extra fuel are combined together in the proper amounts, extra horsepower is obtained. This works similar to the way that turbocharging or supercharging an engine forces more air into the motor, only it eliminates the complexity of having to drive a turbine or a compressor.
Early nitrous systems went into service at full throttle. Why? Nitrogen-rich oxygen allows fuel to ignite with such force that the piston's power stroke magnifies to the point of constantly breaking motors (due to overfilling the engine's cylinder, as mentioned before).
The BoonDocker system, when pressed into service, regulates nitrous and fuel flow amount through throttle position and float bowl pressure. By increasing float bowl pressure, when the nitrous activation button is pressed, fuel flow increases with the increased pressure pushing extra fuel through the carburetor.
The Young-designed system regulates itself via a specially designed nitrous expansion manifold that allows the engine to naturally aspirate nitrous oxide.
We chose a 2003 Arctic Cat 900 1M as our project sled. This 900 1M was already burning up mountains on a Starting Line Products single-tuned exhaust with V-Force reeds. Efficiency and torque were already in our favor.
Cat's 900 is one of Young's favorite motors on which to install the BoonDocker system. He likes it because it's "a big torque-filled twin that utilizes nitrous power in radical ways."
When installing this system though, be sure you have your particular unit's instructions handy at all times. This article does not hit upon the minute details such as which part numbers to connect.
Most nitrous bottles have siphon tubes inside them so the liquid will be drawn out from the bottom just like an aerosol can. However, in a snowmobile's environment there are high levels of vibration- this in and of itself would cause the siphon tube to loosen and move inside the bottle, resulting in inconsistent flow.
For this reason, Young prefers not to use a siphon tube. Instead, the bottle is mounted upside down to directly flow out the valve. In this orientation, the bottle needs to be tipped so the valve is down and toward the rear of the sled at a 20-to 90-degree downward sloping angle.
The most common bottle location is under the hood near the chaincase and close to the exhaust. The bottle should be no closer than about an inch and a half away from the exhaust. This provides sufficient heat to keep the bottle warm when the hood is closed.
The bottle can also be mounted in the seat's trunk. Foam can be removed to fit the bottle, or a special BoonDocker BOSS seat is available with a space already molded for the bottle. For seats without a heat exchanger directly underneath, a simple heater system using hand warmers wired directly to the tail light provides heat for the bottle.
For this installation, the bottle fit easily underneath the single pipe. A bracket was bolted directly to the bellypan and the bottle was secured with two large clamps.
The best place to mount the nitrous manifold is up high on the airbox where the nitrous and incoming air are allowed enough time to mix well before being sucked into the carbs.
For this application, the area under the toolbox on top of the airbox kept things hidden and provided a stealthy installation. Holes were drilled according to the provided template.
After the plastic shavings were cleaned, the manifold was secured with bolts and Loctite
Next, both the carburetor vent lines were connected to the tee fitting on the nitrous manifold. Two small holes were drilled through the airbox to allow the vent lines to reach the nitrous manifold.
Solenoid and Hoses
The nitrous solenoid turns on and shuts off the flow of the high-pressure nitrous.
For this application, the solenoid easily fit underneath the tool-kit area next to where the nitrous manifold is located. A high-pressure steel-braided hose connects from the bottle valve fitting to the solenoid. A small high-pressure nylon line routes from the solenoid to the nitrous manifold.
A push-button switch was attached to the left handgrip where it can be easily pressed with the thumb, or if rotated slightly, pressed using the forefinger.
A rectifier was wired according to a simple diagram included in the instructions. Either a 12V AC or DC power source and ground connection are all that was needed to power the system.
Motor and Nitrous Tuning
When using nitrous, a too-rich nitrous condition will cause power loss. A too-lean nitrous condition will cause power up until the engine seizes. Turning the adjustment screw in will richen the mixture. Conversely, turning it out will lean the mixture. Know that turning the adjustment screw only affects fuel flow, not nitrous flow. Nitrous adjustments are made by replacing orifice plates on the nitrous manifold.
Jetting changes are not required for snowmobiles that vent their carburetors to the airbox. Because this Arctic Cat vented to the atmosphere, we stepped up the jetting one size on the PTO side and two sizes on the magneto side. We did this because the carbs were set to vent through the nitrous manifold and into the airbox.
When large amounts of air flow through the airbox, a slight negative airbox pressure will occur. This will cause the float bowl pressure to decrease, thus decreasing the fuel flow slightly. This is compensated by increasing the main jet size.
A piece of information we feel you should know:
BoonDocker is investigating solutions for EFI applications, ways to adjust timing curves for nitrous use, multistage nitrous systems and bigger horsepower increases for serious racers.
Many thanks to the BoonDocker staff who coached, tutored and assisted American Snowmobiler on this installation. For more information call BoonDocker at 208/542-4411, or visit www.amsnow.com This story ran in the February 2004 issue of American Snowmobiler magazine