Here is something I wrote up a while back:
The flowing of a system is best described as getting a nitrous to fuel ratio (N/F ratio) for your combo that will compliment your engine setup. I will not be going into what N/F ratios are best or safest, as I don’t know.
When measuring these ratios, you have to do it by weight. That is, you are determining the relationship of the amount of nitrous used in pounds with that of the fuel used in pounds.
The next bit of info requires an accurate time delay relay and a very accurate digital scale.
For the best accuracy, all parts and conditions being used should match how you run your car at the track. I personally flow my fogger by taking the manifold off the car and set it right along side the car. The hoses for nitrous and fuel are not changed and are run out to the side of the car.
I put a charger on the battery to help alleviate any voltage drop/variation during testing.
The first thing to do is decide what “shot” of nitrous jets you plan on using. Get your nitrous side all hooked up with the way you’d run it in the car. Remember, you want to keep things as consistent with what you do at the track, so you should have the bottle full and pressure at what ever you use. I use 950. I purge the setup then weigh the bottle to get my starting bottle weight. I weigh it as it sits next to the table/test bench with all the hoses hooked to it. That way the only change in weight after the test is the amount of nitrous used, not hoses, nitrous in lines, etc.
Now you need to turn on just the nitrous solenoid(s) with the time delay relay. I flow it for 10 seconds since it is good round easy to work with number. After it shuts off, check the scale and calculate out how much nitrous was used.
Lets say three pounds were used. Lets also say we want a N/F ratio of 5:1. Since we used three pounds of nitrous, that would equate out to .6 lbs of fuel (if you can’t figure out the math, you shouldn’t be doing this).
We need to figure out the fuel side next. There are more accurate ways to measure the fuel (they are posted in the nitrous forums back in Oct ’03) but I’m only going into weight here. You’ll need to find a bucket or container of some sort to flow the fuel into. With a fogger, it really doesn’t spray all over the place so a container that held the manifold worked fine.
The first thing to do is find the tier weight of the container. With my scale, I simply put the container on it then reset the scale to zero. That way, when I put the container back on the scale, it is only measuring the weight of the fuel, not the container. For each test, you will want to zero out the scale. Temperature and pressure I have found both will affect the accuracy of a scale so as it gets colder or hotter through the day, your scale may change, so best to zero it every time.
To be safe, make sure the nitrous bottle is closed and that you are only going to be activating the fuel solenoid(s). Now, flow the system for 10 seconds just like the nitrous side (remember, a time delay relay is needed for this to be worth anything – no stopwatches). Don’t forget to turn the fuel pump on. Also, use the same fuel you use at the track.
After the system shuts off, wait a bit for all the fuel to drip out. Remember, the engine is pulling vacuum on this stuff and will suck that fuel out so you need to make sure it gets out as well.
Now measure the weight of fuel. Lets say it is at .68 lbs. (I am using pounds here for ease of reference, you really need to use the smallest measurement your scale has, e.g. ounce or grams.) Well, that is too high, so go turn the regulator down a bit (1/4-1/2 turn – just guessing here). Right now, fuel pressure does not concern us in the least. We are interested in the weight of the fuel. Retest the system until you can get it to flow .6 lbs (or whatever number it is you need to get) at least two times in a row.
So now we have your system spitting out the N/F ratio you are happy with. We have to figure out at what pressure it is at so we can keep a log of this info and be able to tune at the track. For this you’ll need some sort of flow tool utilizing a high quality gauge. DO NOT use a glycerin filled gauge. The sealed gauge causes considerable fluctuations in readings… even the fancy ones that have a burp valve. An empty faced (air) gauge or digital gauge is what you want.
Pick out what jet you are going to use in your flow tool. The number can match the size in your nitrous system or it can be an arbitrary number. It doesn’t concern us what it is. The reason being is, we already know that we have the N/F ratio that we want. We just want to see what the fuel pressure is at so that we can use this info at the track. The only thing that the flow jet’s size changes is the fuel pressure READING that we get. For instance, if you use a small jet, it may read 6.5 psi. If you use a jet matching what was in the system for the weight testing, it may read 5.5 psi. We didn’t change the fuel pressure, only the READINGS we got changed. The system will still flow the required weight of fuel. So what we need to do is write down the flow jet number by your results so that you can use the same one at the track. If you wanted you could just use one flow jet for all your horsepower jetting settings. So if you flow another horsepower jet setting and use the same flow tool setup (jet and all), just be sure to write down your results. The main objective you are wanting is to dial in the same fuel pressure at the track as your test results gave you.
With that all said, I personally like to check the fuel pressure, re-flow the system to make sure the same weight comes out, and then retest the fuel pressure again.
Now lets address the question of whether or not to check the fuel pressure through a solenoid, lines, plate, or whatever to come up with what you need. It all depends on how you did the above or how your tuner did it. Yes, there are going to be difference between flowing just off the regulator or flowing through a solenoid and hard lines. But all of it doesn’t mean a thing if you don’t know how it was flowed in the first place. You can check your fuel pressure anywhere after the FP regulator. It doesn’t matter as long as it is the same place that it was initially checked during the N/F flow testing.
I sure hope this makes sense.
Don’t assume that because you just flowed your system, you are ready to go to the track. Check your fuel pressure at the track! Temperature and barometric pressure affect some of the regulators quite significantly.
There are many variables that are out there that doing these tests do not take into account. For instance, it doesn’t take into account that the nitrous and fuel don’t flow individually, they flow at the same time. On a fogger, this is paramount, as the flowing of each through the nozzle will affect the results. However, to measure both at the same time would be very messy without the proper type of container to capture all the fuel flying around while not hindering the nitrous – ie, you can’t just use a sealed container since the nitrous would blow it apart. Not only that, you have a bunch of pistons that are pulling a ton of air by your nitrous equipment that will also affect the flow rates. Then you have to consider the affects of your car launching and how that affects the fuel pressure (not to mention deadhead regulators that spike to line pressure before being turned on). So what I am saying, while scientific principles are used in doing this stuff, they are not the tell-all of any particular nitrous systems affects on your engine combo and final Air/Fuel ratios.