How To Properly Size, Mount And Install Your NOS Nitrous Bottle

Author: Jason Reiss | 06/03/2021 < Back to Motor Life Home

The process of selecting and mounting a nitrous bottle for racing success isn’t as simple as you might think. Like everything else that is related to motorsports, there’s a science to it. Nitrous Oxide Systems (NOS) has been at the nitrous oxide game longer than just about anyone when it comes to adapting nitrous oxide injection to racing and enthusiast automobiles. Rather than guess at what the science might be to select a bottle and its mounting configuration properly, we cornered Jamie Wagner, Engineering Supervisor NOS Test Engineer at Holley Performance Products (NOS’ parent company), to determine just what the science says. In the process of that phone call, Jamie shared many other tidbits of running a successful nitrous combination, and we felt obligated to pass them along to you.

Bottle Basics

Let’s talk about the details. The bottle is more than just a container, though—there’s technology baked into it that is designed to maximize system performance. Currently, NOS offers several bottles for automotive use. Most notable is the familiar blue bottle, which comes in 2-pound, 2.5-pound, 5-pound, 10-pound, 15-pound, and 20-pound sizes. There are also black, polished, and orange Sniper bottle versions. Most use the NOS Super Hi Flo valve to discharge nitrous when the bottle is open, but it’s important to note that the 2-pound and 2.5-pound bottles use a small bottle valve and the Sniper bottle uses the NOS Hi Flo valve, which has a smaller orifice and is designed specifically for use with the Sniper nitrous systems. Lastly, there is a carbon fiber bottle.

“The blue 10-pound bottle sells thousands of units a year by itself. The blue bottle is an iconic part of nitrous,” says Wagner.

“All of the bottles that are considered a carbon fiber bottle actually have a super-thin aluminum bottle under that. The carbon weaving is carbon fibers but not the carbon fiber that we look at in an automotive application that has a weave; this is carbon fiber threaded material that is wrapped around the bottle to strengthen it. That way, you can use thin aluminum to reduce weight, then the carbon fiber material strengthens that, then there is an epoxy finish,” he says.

He shared that the carbon fiber bottles are the same type of bottle carried by firemen for oxygen purposes when fighting fires. As you might imagine, the lighter the fireman’s gear kit can be, the better off he is when faced with a difficult firefighting position. This usage also proves out the bottle’s capabilities in those types of situations.

The weight of a full bottle—depending upon construction—can be a significant difference, critical when you’re in a racing environment where every ounce matters from a weight balance and weight break perspective. Full, the carbon fiber bottle weighs 21 pounds, 9 ounces, and contains 12 pounds, 9 ounces of nitrous. The traditional blue all-aluminum bottle weighs 24 pounds, 12 ounces full, but contains only 10 pounds of nitrous. So not only is there a difference of more than three pounds full, but the carbon bottle also contains nearly three more pounds of nitrous oxide, which matters when the nitrous system (or multiple systems) requires a large gulp of giggle gas. Alternatively, a racer can use the carbon bottle but short-fill it and have an adequate amount of nitrous but be carrying less weight down the track.

One thing to note regarding carbon fiber bottles: traditional bottle heaters are a no-no. These require the use of a bottle water bath system instead to avoid compromising the carbon fiber epoxy coating. A wrap-around bottle heater has the potential to cause a big problem, according to Wagner.

Bottle Size vs. On-Track Performance

Nos Bottle Pressure

When a bottle is heated to the proper temperature—between 85 and 95 degrees Fahrenheit—the nitrous oxide will reach between 900 and 1,000 pounds per square inch of pressure inside the bottle, which is the proper pressure to begin delivery to the engine.

When stored in the bottle, nitrous oxide is primarily a liquid, and when stored at room temperatures produces between 600 to 800 pounds per square inch of pressure. To maximize the volume exiting the bottle, the temperature is raised by a bottle heater (wrap-around or water-bath) to produce a bottle pressure of 900 to 1,000 pounds per square inch. As the system opens to the engine, it is injected as a gas that consists of two parts nitrogen and one part oxygen. It is this oxygen molecule that allows increased power from an engine when the appropriate amount of fuel is added to the mixture. It’s a bit more complicated to deliver the nitrous to the engine than one might think, though.

“Nitrous has to change to a vapor [at the engine] to be functional. You want to get as much of the nitrous you can to the nozzle, and it needs to be liquid. When it’s in the bottle, and you’re getting 950 psi, that’s when it becomes a supercritical fluid, where it’s neither a liquid nor a vapor and kind of both at the same time. As soon as it goes above or below that critical temperature/pressure point, it turns into all liquid or all vapor. You have the balancing act of the two to get it from storing it in the bottle to getting it into the engine where you can use it—getting the nitrous from the bottle through all the lines, fittings, and solenoids. In a completely full bottle, it has 10 pounds of nitrous in it that is all liquid. As it gets used up, above the liquid is the vapor, and that’s what’s developing the pressure. There’s a balance between pressure and temperature, and liquid and vapor. Every time it goes through a transition, from the bottle to the nozzle, there can be a pressure drop, and if the pressure drops enough, it turns from a liquid to a vapor and screws the flow up,” says Wagner.

So buying a bottle isn’t as simple as just saying, “I’ll buy the biggest bottle I can to get the most runs out of it at one time.” If you’re trying to get the maximum performance out of the system, it’s important to size the nitrous bottle accordingly. This is where the advice of a seasoned nitrous technician comes into play; Wagner did recommend calling to ask for assistance with sizing the bottle correctly—and filling it with the ideal amount of nitrous for your particular application—if the possibility exists. Systems bought in kit form are typically optimized with lines and fittings to work correctly with the bottle size, jet size, and expected horsepower goal.

Contrary to what you may believe, the fuller the bottle is when you activate your system, the more quickly you lose bottle pressure because the nitrous needs to change states to keep the pressure up in the bottle. Stuffing 11 pounds of nitrous into a 10-pound bottle—while it is possible—is detrimental to performance.

“It takes time as the liquid nitrous comes out of the bottle to turn the remaining nitrous into vapor inside the bottle so it can continue to push out. A bottle that is not full already has vapor in the bottle and is pushing at the same time. It doesn’t have to change states as quickly on the bottle that already has some vapor in it compared to the bottle with no vapor,” says Wagner.

How Long Does It Last?

NOS super hi flo valve

The Super Hi Flo valve utilizes a handwheel that is integrated at a 45-degree angle to the nitrous flow, which assures maximum performance capability.

He stresses that nitrous usage depends on many factors. If you are not using a pre-built kit, then the factors that affect usage include engine size and system size. Ideally, a system is flowed to see how much nitrous it consumes over time. For example, you would weigh the bottle before the test, run it for a predetermined amount of time, weigh the bottle again, then figure usage in pounds per minute, or second. It is not as simple as pointing to a system and saying, “you’ll get five runs before the bottle is empty.”

“Everything is dependent on the combination. A much less efficient engine—let’s say a completely bone-stock small-block Chevy—will make more power given the same volume of nitrous compared to a well-built, super-efficient small-block Chevy. Nitrous makes a huge difference in the low-efficiency engine and much less difference for the high-efficiency engine,” he explains.

“Let’s say a .030-inch jet makes 150 horsepower on one engine, and on another engine, it may make only 80 horsepower. The engine’s efficiency, intake, cylinder head design, exhaust, and camshaft profile all play into it. So saying that a given volume of nitrous will make X horsepower is a rule of thumb but is not super accurate,” he says.

In essence, once you get away from a pre-built kit, “how long it lasts” is a question that’s difficult to determine without running the system on your particular car.

Mounting Your Bottle

NOS Siphon Tube

Siphon tubes are straight until they get close to the bottom of the bottle (how far down depends on bottle size), where there is a 30-40 degree bend in the tube. The bend in the tube is also directly opposite the bottle’s label, and on the same side as the outlet.

There’s a reason that the bottle brackets that ship with a complete system are oriented in a specific fashion, to raise the nose of the bottle—because the siphon tube inside the bottle is also oriented in a particular manner, as is the label on the bottle. These three things work in conjunction to help you get the most nitrous you can out of a bottle.

If you are running a race vehicle that has the bottles standing in the passenger compartment, then you want the label facing the front of the car, with the outlet pointed toward the rear of the vehicle, as the siphon tube points toward the back of the car in this orientation. Although, in this configuration, some racers install straight tubes into bottles that are standing straight up.

The third bottle orientation would be in the case of a bottle that is mounted perpendicular to the vehicle’s chassis, and not at an angle (flat in the trunk, for example). Here, you’d want to rotate the bottle in the brackets so that the label faces toward the front of the vehicle, so on acceleration, the nitrous is being pushed toward the siphon tube.

Most importantly, if you purchase a bottle that is not new, take it to your local bottle recertification facility to have it inspected and tested. Simply search your local area for a facility that certifies oxygen bottles. It’s an inexpensive investment: under $50 in most areas.

Blowdown Tubes

NOS blowdown tube

Each vehicle with a nitrous bottle in the passenger compartment requires a blowdown tube mounted to the bottle, in the event of a failure of the pressure release device.

With all of the talk about siphon tubes, we would be remiss if we didn’t also mention blowdown tubes and explain their function, which is wholly related to your safety as the driver of the vehicle. Racing sanctioning bodies typically require a hardline blowdown tube installed on every bottle in a nitrous-injected entry, and for good reason.

“If you have a hatchback car and you’re making a pass and blow the line off or the bottle overpressures, it has the ability to fill the cabin up with racing nitrous, you’re going to suffocate and pass out and have problems,” he says.

“The blowdown tube is mounted to the pressure release device, which houses a disc that ruptures at approximately 3,000 psi. It vents the nitrous outside the car.”

Also of note: when installing a blowdown tube kit, when you install the valve, it is critical to install the fitting to the exact torque value specified in the instructions. If it is over- or under-torqued, it will blow out early or late, or at a much higher psi than the design parameters call for. Especially on the high side of that equation, the pressure becomes an issue concerning bottle integrity.

In Conclusion

NOS bottle mounting

If the bottle is positioned in a set of mounting brackets, the valve would typically be oriented at the front with the bottom of the bottle at the rear. When installing the bottle into the brackets in this orientation, the label should face toward the sky, which puts the bottle outlet toward the bottom of the vehicle, along with the siphon tube toward the bottom of the bottle.

It’s not as simple as slapping a bottle into your car and pushing the go button; there are other considerations to take into account. Hopefully, we’ve presented the information clearly and concisely for you to reference as you take the exciting journey that is nitrous oxide injection. Enjoy the juice—it’s worth the squeeze!

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