At what PSI do you refill a NOS bottle?

[Sean Roe]

As per the title of this post, I need some advice on what pressure to let a bottle get down to before refilling.
Currently, it's at 650 psi.
With a single 0.065" jet in the intake, the car is at 813 RWHP and 899 RWTQ, but we are considering going to a larger jet.
This is MBN's 2002 FE car from Bill at Woodhouse that we put a blower, heads and pistons in. The car is at 712 RWHP and 755 RWTQ without the NOS.
Thanks in advance,
Sean

 

[BigCarrot]

The PSI has nothing to do with it. You need to weigh the bottle. The pressure will fluctuate with the temperature. If you've used it much, chances are that it needs a refill. Bottles don't last a terribly long time with a big shot.

 

[RedGTS]

Sean, I have no firsthand experience with nitrous, but the guys I know who use it seem to follow Big Carrot's advice. They talk about refilling it when it gets down to 20% full, and they weigh the bottle to see how many pounds of nitrous they have remaining. Most of them like bottle pressure between 900 and 1,050 psi for optimum power, but as Carrot said, that's not the best indicator of when to refill.

Or, you could just finish up the intercooler, remove the nitrous system, and crank up the boost.

 

[Tom Welch]

Sean,

Bottles are re-filled via a pressure differential. The little bottle should be frozen to achieve low pressure and the large bottle should be at about 85 degrees for optimum filling. Fill by having the small bottle sitting on an accurate bathroom scale (adding the filling adapter to its weight from the bottle label) and opening the valve on both bottles. You will note that as the bottle begins to fill, its pressure will begin to rise and you can see the frost melt off of the little bottle from the bottom up as nitrous enters. Close the bottle valves at the deisired weight...this can be found on the little bottle's label.

Aftermarket filling pumps are also available. They make filling easier, but I still recommend cooling off the little bottle if possible for a quick fill. I use both methods at my shop.

Tom

P.S. If you are using NOS sprayers, you have reached the maximum amount of flow through the nozzle with a .063 jet. NX "Shark" nozzles will flow up to a .073 Jet before the nozzle becomes the restrictor. You are almost at maximum flow now. Just my $ 0.02

 

[BigCarrot]

Pffff, like Tom knows what he's talking about! Yeah right.

 

[MES]

Sean where did you put the single nozzle? Wouldn't it be better to use 2 in front of the throttle bodies, one on each side? Also what PSI did you have when you gained the 100rwhp from the nitrous. Thanks

 

[SapphireGTS]

Look at this. Tuners working together for higher horsepower world.

 

[Sean Roe]

Thanks for all the input and information.
Believe it or not, I had never used NOS before this car. There just isn't much call for it in road racing (that I've ever known of). I really didn't know that much about it and did the tuning part based on input from Tom and Tony.
Yes Tom, these are parts from a NOS brand universal EFI kit with a 10lb bottle (ordered it from Summit before I knew you were a dealer). It has a fogger nozzle that has a fuel port we are not using. Thanks for the info regarding the jet size, we were thinking of maybe drilling one out to 0.080". If we do that, I'll check to see what the port size is inside the nozzle. Maybe we can use the fuel port part and run a second smaller NOS jet instead.
Regarding the HP and nozzle part, this shot seems to make 100 RWHP (we've tried it at 8.5 and 10 psi only). The NOS kit was advertised at having jets from 75-125 HP, so it seems on target. The fogger nozzle is in the passengers side intake tube just before the inlet of the Supercharger.
Funny enough, this motor doesn't seem to need an intercooler at this boost level Ronnie. I put a K Type thermocouple in the intake manifold and have been monitoring cruise and full throttle pull temperatures. We even used the second part of the NOS jet (the fuel part) and NOS jets to run water, water alcohol, alcohol injection tests. At these HP levels, even with the NOS, there is no sign of any detonation at all on the plugs. We've done about 42 dyno pulls on the motor and numerous pulls on the air strip test track. The maximum intake internal temperature after a long pull was 203 degrees with an ambient of 68-70. With the NOS on, it was 192. A lot of it has to do with the camshaft profile as Comp Cams custom spec'd the cam for this particular engine. She's flowing a lot of air through the cylinders with overlap and I think that's helping keep things cooler in the chamber.
Here are the dyno pulls from yesterdays tuning tests:

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I have to work on making the NOS pull smoother. Not sure if a choppy fuel curve is normal with NOS.

Thanks again,
Sean

 

[utahviper]

That dyno sheet looks alot like mine. Love the flat torque curve. 900RWTQ is a boat load! That should be enough for a nine second pass down the drag strip with a proper setup.

Great Numbers!

 

[Sean Roe]

That dyno sheet looks alot like mine. ...

That's one of the reasons I tried to reach you at the end of the day yesterday.
I thought it was kind of coincidental that the numbers were so close to yours when your company supplied the computer system for the dyno.....

 

[Jack B]

On the Gen II, the a/f curve is fairly smooth with the nos activated. What is strange is the negative change in hp/torque at 4000. This coincides with the bubble (increase) in a/f.

 

[ChoiceViper]

This might be a dumb question, but why not step up to a 20lb. bottle when running bigger shots/jets. Less filling vs. more weight?

Dave

 

[Jack B]

The next common bottle size is a 15#. Size constraints become an issue.

 

[1TONY1]

You hit on my suggestion Sean, use the fuel side for another nitrous jet. Nos does not make a y fitting in the smaller line sizes, they only make a tee, but it should work fine. The other option would be to use two nozzles (you can get single inlet nozzles, nitrous only) I think you could play with the one nozzle and step it up a fair amount. I would never run a bottle at less than 50% to 60% and if I were looking for best performance it would be higher than that. On the outlaw car, we run two fresh bottles on every pass. We carry 12 nitrous bottles and a nos pump with us to the races.

 

[ACR Joe]

N2O is a liquefied compressed gas which has a vapor pressure of 745 psig. Unlike a non-liquefied compressed gas (i.e. N2, O2, Ar, He, etc.) the cylinder pressure will remain constant as long as liquid remains in the cylinder (same as CO2, HCL, CL, etc.). Once all the liquid has flashed to the gas phase, the cylinder pressure will begin to drop. At this point nearly all of the N2O has been consumed. Accordingly, weight is the only means of determining how much product remains in the cylinder. Once the cylinder pressure begins to drop, the cylinder is essentially empty. I'll take off my Praxair hat now.

 

[Sean Roe]

On the Gen II, the a/f curve is fairly smooth with the nos activated. What is strange is the negative change in hp/torque at 4000. This coincides with the bubble (increase) in a/f.

Hi Jack,
That's one of the reasons I was asking about when to refill the bottle. I'm going to take it out and weigh it as per the advice above (and from e-mails). I didn't want to spend a bunch of time tuning and trying a bigger jet if the bottle was getting low. The next tuning change, other than more NOS, would be to add about 10% more fuel at 4,000 and and see if the power flattens out. For whatever reason, you don't feel that dip when driving the car and there's no change in any of the programming at that point. It might be some sort of dyno anomaly due to speeding up the roller so fast when the NOS comes on (I'll ask Dynojet).

Now, on to the second part of the when to refill the bottle question. If it's not based on pressure, but instead on weight, I assume we should have it refilled if below 50% (5 lbs NOS) as per Tony's suggestion above? How low is the absolute lowest weight before you should not use it and have it refilled?
Man, it's great to come to this board and ASK questions

Sean (aka NOS Newbie)

PS, just saw Joe's response. Thanks Joe, that helps clarify things also.

 

[Cudaman]

Sean...... How many times have you help a Newbie out????

Aslo helping out other tuners?????

Cudaman

 

[1TONY1]

Once the cylinder pressure begins to drop, the cylinder is essentially empty.

I guess you need to explain that to me again for me to totally agree


Cylinder pressure on a nitrous bottle when used in this way is related to the bottle temperature. A fraction of a second after the nitrous solinoid is opened the "pressure begins to drop"...... we know the bottle is not empty at that time. Pressure is somewhat related to the amount of nitrous but in this application is mainly controlled by the temp. A full bottle can be 600 psi at 50 degrees and 900 psi at 85 degrees (ballpark numbers) so I don't understand your pressure theories. Maybe things are temp controlled and/or different in the commercial enviroment.

 

[Tom Welch]

Temperature is the controlling factor. A bottle at 900 psi with a heating element in place or located in typical summertime weather, will maintain pressure and flow rate until completely dispensed. Without proper bottle temperature control, the horsepower output will be significantly affected.....REGARDLESS OF AMOUNT OF NITROUS IN THE BOTTLE. A full bottle of nitrous at 600 psi will provide less flow than a near empty bottle at 1000 psi and resultant power gains will show accordingly.

We now use a bottle heater (NX) that uses a pressure transducer to maintain optimum pressure by regulating the heating element for pressure.

It's pretty simple folks.......the bottle has a label on it that shows the empty and full weight of that particular bottle. The bottle has a gauge on it. Fill the bottle to the placarded weight and maintain constant pressure by heating with an automatic heater in cold ambient temperatures. When the bottle weight is depleted to nearly that of the empty bottle, refill.

Tom

P.S. For those inquiring minds about refilling nitrous bottles, I can fill a nitrous bottle in less time than it takes me to fill my Viper with gasoline, and I fill it with gasoline more often than filling my nitrous bottles!

 

[1TONY1]

Nitrous Oxide Systems now has a pressure based bottle heater ..... AND a LED (blue lighted) purge kit...woohoo