Nitrous oxide is an oxygen carrying compound that increases horsepower. The more oxygen and fuel you can stuff into an engine, the more horsepower you get back.
At approximately 565 degrees F, nitrous oxide separates into two parts oxygen and one part nitrogen. This added oxygen speeds up the combustion process. If extra fuel is added during nitrous injection, the result is similar to a supercharger. Extra fuel is needed, otherwise disastrous, damaging results will happen to an engine.
Nitrous oxide has this effect because a cubic foot of it contains 2.3 times as much oxygen as a cubic foot of air. By substituting nitrous oxide for the air going into the engine, more horsepower is created. We installed a BoonDocker kit on our 2005 Ski-Doo Mach Z demo snowmobile.
2005 Ski-Doo Mach Z Installation
The BoonDocker nitrous system we installed on our 2005 Ski-Doo Mach Z demo sled can use an optional control box that hooks into the electrical system to control the fuel supply to the engine when nitrous is added. The control box connects between the sled’s engine control unit (ECU) and the throttle bodies.
When not using nitrous, the EFI control box can be used to modify the existing fuel map while keeping the stock fuel map. It’s a nice feature to be able to fine-tune fuel delivery in the same way as changing carburetor jets. But be careful because it’s possible to go too lean and end up with an expensive repair bill.
The control box still allows the ECU to compensate for such variables as engine speed, throttle position, barometric pressure, engine temperature and air temperature. If you don’t want the control box to interfere with the ECU, unplug the control box and plug in a jumper connector.
The wiring harness for the control box installation needed to be hard wired into the fuel injector harness, which required removing the Mach Z’s headlight and windshield from the sled. We removed the protective covering from the harness and exposed the fuel injector wires, then spliced and soldered the connections.
Next, the nitrous oxide bottle was to be mounted upside down and at a slight angle toward the rear of the snowmobile. This ensures that liquid nitrous, rather than vapor, was drawn from the bottle. For correct installation, the exhaust had to removed from our Mach Z – both the expansion chamber and the silencer.
The bottle bracket required drilling a hole to mount the bracket to the side of the bulkhead, which wasn’t mentioned in the instructions. After mounting the nitrous bottle in the bracket, and test-fitting the exhaust, there was a clearance problem. After a call to BoonDocker, we learned we needed a smaller aftermarket exhaust silencer. The best placement for the nitrous bottle is close to the exhaust to help keep the bottle warm. BoonDocker says the system works best if the bottle is kept between 70 and 90 degrees F.
The BoonDocker system uses nitrous manifolds that are installed in the airbox to deliver the nitrous oxide to the intake system. The airbox needed to be removed and separated from the Mach Z’s side panel. Two manifolds were installed into the airbox, which required drilling both a 3/4- and a 1/4-inch hole. A template was included for this procedure. After installing the manifolds, we cleaned debris from the airbox.
We installed the solenoid/pressure transducer on the clutch side of the snowmobile. The pressure transducer monitors bottle pressure. Fluctuations in bottle temperature greatly affect nitrous pressure, which affects nitrous delivery. The control box monitors pressure changes and adjusts the fuel delivery as pressure varies.
The solenoid is the valve that allows the nitrous to release into the intake system. There were two, 1/8-inch hoses that connected the solenoid to the manifolds in the airbox. There was also a braided hose that ran from the nitrous bottle to the solenoid. We were sure to route this hose away from the exhaust. The “fun” button, which delivers the boost, was mounted on the left handlebar within our thumb’s reach.
The next step was to hook up the wiring harnesses. We had a minor problem with the nitrous solenoid connection. There was supposed to be a male and a female connector, but instead, there were two male connectors. We simply cut the connectors off and soldered the wires together.
After everything was connected, we performed some in-shop testing to make sure that the system was operating properly.
With the engine off, we opened the nitrous bottle valve and checked for leaks. Also, we checked that the solenoid did not discharge nitrous without pushing the button. Then we turned open the bottle valve and pushed the button for about one second. The engine rpm increased from idle, so everything checked out. We were ready to hit the lake!
Calibrating the system should be done with a full nitrous bottle that is 70-90 degrees F and pressured 700-1000 psi. It’s also important to make sure the engine is at normal operating temperature. We recommend having a spare bottle full of nitrous to spend some time fine tuning the system.
Fine tuning is where the control box comes into play. The control box has a menu that displays information about the BoonDocker system. We accessed each of the five different fuel maps at 3000, 5000, 6700, and 7800 rpm ranges to make adjustments.
Each rpm range had four separate areas of adjustment. There was a low-load adjustment that affects throttle settings from 0 to 1/3. A medium load range condition affects throttle settings from 1/4 to 3/4. The high setting affects throttle positions from 2/3 to full open. There is also a trim adjustment for the PTO cylinder, which allows adjusting each cylinder independently. It’s a feature that can come in handy when installing twin pipes that require a different fuel supply for each cylinder.
The range of adjustment is from -20 to +99 (-20 being the leanest). We used the pre-programmed fuel map included in the control box. The control box also regulates the nitrous menu. This screen is used to make fuel adjustments for nitrous use, and it also displays nitrous bottle pressure. Pushing the nitrous button releases the nitrous oxide and increases the fuel delivery at the same time. There is an adjustment for compensated fuel delivery when the nitrous is discharged, another calibration during fine tuning.
The nitrous is controlled by replacing the nozzles in the nitrous manifolds located in the airbox. The system comes with three-, four- and five-hole nozzles to choose from – five-hole delivering the most nitrous oxide. Each step up is equivalent to an additional 4-5 hp.
We tested and ran our radar runs with the five orifice nozzles (maximum power) starting with the nitrous fuel compensation at +50. With the conditions we were in, it was too rich. We then started lowering the fuel settings until we were at +45. This made a lot of difference and the system started to work well. Keep in mind, we tested in less-than-ideal conditions: 45-50 degrees F and on soft ice.
Our Ski-Doo Mach Z’s track had 168 Stud Boy studs, but it still spun a lot even on soft ice. It took almost a full bottle to get it tuned where it started to perform well. On radar, the results show some nice improvements in acceleration. We would start the runs from a dead stop, hit the throttle wide open and push the nitrous button when we could see the engine rpm start to drop from getting a good hook up. The rpm jumped up and we could feel the acceleration in the saddle.
We could feel the acceleration because the fun button worked! As seen in our data chart, the overall speeds and elapsed times (ETs) to our distances were dramatically improved.
During our first nitrous run against the radar, our bottle was empty so the run was discarded. During the second run, Nitrous 2, our timing was off. We pushed the button early, which lugged the engine briefly. Our nitrous runs 3 and 4 were the most applicable and are represented in the average. Our stock runs were consistent and by comparing the average stock runs with the average of runs 3 and 4, we produced good, measured performance increases.
The stock average time to reach 660 feet was 8.34 seconds. Runs 3 and 4, on the bottle, were 8.10 and 8.00 seconds, respectively. The power boost also produced speeds at 660 feet that were more than 5 mph greater. BoonDocker’s nitrous unit weighs 6.1 pounds full and 3 pounds empty. It is important to remember that it cannot be stored on the machine.
Because the greatest nitrous benefits are at peak horsepower, the results are more impressive at 1,000 feet. When using nitrous on run 3 we peeled 0.33 seconds off the stock average 1,000-foot ET, and 0.48 seconds from the ET during run 4. It was thrilling to feel, too.
Pure, Unadulterated Fun
Though our results were already impressive, we left our test grounds with empty nitrous bottles thinking we could have seen even greater performance with more testing time.
The BoonDocker nitrous system has a lot of good features, but it isn’t easy for the garage mechanic to install and set up. The fine-tuning of the system, like with any highly modified system, takes strong knowledge of engine tuning for maximum performance. One thing that would make it easier would be to have exhaust temperature monitors installed, which would help to find the rich and lean settings.
BoonDocker only recommends holding the button up to eight seconds at a time, which, if you’re a drag racer or a mountain rider, might be all it takes. With the experience we had that would be about 10 to 15 runs with a 3-pound bottle. The good thing is nitrous oxide gas is cheap. According to BoonDocker, most auto performance shops carry nitrous and many snowmobile dealers soon will, too. BoonDocker also sells portable 20-pound bottles complete with a transfer line, filter and a digital scale.
For the performance gain, we like the BoonDocker system and were pleased with our results. The pure, unadulterated fun of pressing the little red go-fast button was addicting.