One of our customers gave us a call and was looking for some in-depth information on bottle pressure. Looking around lately I’ve seen a lot of debates on other forums as to what is the best bottle pressure to target. We have our preference for various reasons, but what I'm going to get into is, what happens to nitrous oxide at various bottle and line pressures.

The first thing we have to understand is the temperature/pressure relationship. Take a look at this graph I quickly threw together below of which we’ve all seen before. This shows the relationship of temperature and pressure (k=P/T). Pressure (P) of any substance, more specifically nitrous, is in direct proportion with temperature (T) when pressurized in a contained vessel. As we increase the temperature of the bottle, we see a direct result on pressure in the same direction. The continued vaporization of the liquid nitrous is a direct result from the increased temperature/pressure relationship and can be coined self-maintained pressure regulation. As the temperature increases the liquid expands, meaning it becomes less dense. I also have attached a graph showing the density of nitrous oxide at certain temperatures. As you can see from the first graph, the higher the temperature, the higher the vapor pressure levels. This causes the liquid to expand and vaporize, therefore decreasing the density of the substance. How does this affect you? In using nitrous oxide you want to keep the nitrous oxide in liquid form, dense and cool. This is why keeping line length on direct ports to a minimum is also important. Engine temperatures can heat soak the lines and raise the nitrous above its critical temperature before it exits the nozzle. This we do not want, phase change should occur in the runner, not in the nitrous lines. Think of heating water from liquid form to vapor. A cubic foot of water vapor is fractions of the weight of a cubic foot of liquid water. Same principal with nitrous oxide, it just does it at different temperatures and pressures. Taking it one step further, lets not negate the cooling effects of nitrous in an intake manifold…and what do we know about cooler air? More dense, is it not? So yet another indirect advantage to getting the nitrous charge as dense as possible.




The critical pressure of Nitrous Oxide is 1069psi. This is the upper most pressure required to keep Nitrous Oxide in the liquid phase and anything beyond that is not necessary. Taking it a step further, any substance which goes beyond its critical pressure and critical temperature (critical point) becomes supercritical. Matter can occur in three states, Liquid, Gas and Solid. When liquid Nitrous Oxide reaches supercritical (>1069psi and 97.7F) it becomes neither a liquid nor gas, but actually takes on characteristics of both. Some believe it resembles foam and as you can imagine this changes its velocity through the main feed line as well as any consistency in mass flow. It also results in a premature phase change into a gaseous form before it ejects from the nozzle. As was stated earlier this is not what we want. We want nitrous to remain in liquid form until it enters the intake. Now above we spoke about self-maintained pressure regulation in the bottle. While 1069 psi is at the brink of becoming supercritical, it does not mean that it’s the ideal bottle pressure. Looking back, besides the poor density, it would take a lot more time and energy for the bottle to regulate itself back to the 1069 launch pressure. Something of which we certainly do not have time for, nor do we want to waste any energy (in multiple forms) on doing so. Self-maintenance of bottle vapor pressure is quicker and more efficient when done at lower launch pressures without negating velocity.

Another thing that must be taken into account, the higher the bottle pressure, the larger range of pressure drop we will see. On smaller shots a large drop is not going to be an issue. When going beyond 200hp you will begin to see bottle pressures decreasing during a run. Again, this is not what we want. The name of the game is consistency and declining bottle pressure will affect your tune up. Therefor, our end goal is to regulate a target pressure not just at the launch, but through out the run as well.

 

great read, cleared some things up. i love the nitrous forum, so informative

 

Damn Mike. Explaining the ideal gas law and everything? Good info here guys.

 

Good post.

 

Thanks Subscribed!

 

So is the under hood temp one of the causes of this?...I open the bottle, purge make a pass then get back in line, by the time i get to run again i purge and i get some air before i get nitrous?

 

Yes you will vaporize the liquid in the line.

Nick

 

Nice write-up

 

So here's the million dollar question (well for me at least) How do you calculate what pressure vs. size of shot vs. length of time spraying, will give you the maximum power, yet yeild the most dense charge throught the run?

I expect an equation by close of business tomorrow. You know the #

 

/this is a great write up, so, does this mean i should wrap my nitrous line in the engine bay with heat wrap? cuz ill do it!! lol!!

this was a great read up, one more reason to couple my harris/nx system with a nano bottle. thanks man.

sticky?

 

i would think that maintaining the bottle press. with a nano sys. becomes more benefical than a bottle heater, but what is the ideal press.? 900? 950? or 1050? ect. fact, my supply line runs the entire length of the car [ trunk to eng.] and so i purge for what seems a very long time compared to some videos i have seen. does a 15lb bottle hit a bit harder than a 10lb bottle?

 

No, the fact in most cases is the lower pressure from the beginning of the run will yield less pressure fluctuation throughout the run. Nano will allow zero fluctuation, but shouldn't be needed if you jet for the lower pressure. The 15lb bottle will also lower the fluctuation throughout the run. If I did more bracket racing or index racing, NANO would be awesome. Dial an EXACT pressure every time for exact repeatable results. For the test and tune crowd, similar results can be had by simply jetting for and using lower pressure.

All bets are off when you start hitting above 200 shot like Mike said though

 

The charts will look a little different with NANO because you will have 1050psi if the bottle is inbetween 40-80 degrees. With NANO we can calculate how many runs per bottle because all of the nitrous in the bottle is usable. The NANO system will force nitrous more dense at higher temperatures because no heat is needed. Above 85 degrees nitrous will take over from the heat causing the pressure to go up.

With a heated system the more nitrous you use the less dense the nitrous is. The charts are based off of a full nitrous bottle. The reason is because the more nitrous you use, the more room in the bottle for the nitrous to turn to vapor form. Less nitrous=heating more to get up to pressure.

 

so if you jet for 900psi and your goal is 150hp, then the jet size would have to be smaller compared to 1050psi. and if a kit is designed for 1050psi and you run 900psi will you be running more hp? and if true then 150jet set-up would woul be maybe 170? is this right? so what's the ideal psi?

 

The problem is, if you jet for 1050 running a 150 shot, depending on the time sprayed, you will be at 900 by the end of the run--running rich. Now if you jet for 950, you will have much less fluctuation at the end of the run. Making power throughout the run, instead of diminishing power by the end.

 

Most companys have a recommended pressure of where there particular system works well at. Some solenoids cannot handle above 1000psi. Although most of the time when a solenoid does not open it is usually a ground or wiring issue. Personal preference is usually what calls out for the pressure.

When i jet customer cars i have had customers start out with there standard system before NANO anywhere from 850psi to 1150psi. Like i said ask your nitrous manufacture for there recommended pressure or find where you like best. With NANO our starting pressure is always 1050psi and 950psi flowing down track.

 

Amazing Post, Thanks for the info!

 

There was a good discussion about this a long time ago. One guy was talking about how he ran 1400 or so psi, made higher average power, and discussion ensued. I think one of the advantages of the nano setup is having consistent pressure without heating the bottle. You are getting a constant pressure while flowing a higher density nitrous through a static line.

I'll see if I can find that other thread.

 

1400 psi is insane...i would think the solenoids wouldnt open under that much pressure.

 

and people think its as easy as throwing on a kit... haha.

good write up guys! making me want to convert my HSW kit to NANO..