Very well written article except for this part. I am sorry, but I have to interject. I race a dry kit and this is not how it works. NOS was the first company to offer a dry nitrous kit for a late model mustang efi. The way it works is very simple. The early fox's and SN95's have a fuel pressure regulator that regulates how much pressure the fuel rail sees. For every one pound of increase in fuel pressure, the injectors flow more fuel for each given pulsewidth. A pulsewidth is a digital wave that goes on, then off for a specific amount of time. In other words, the injector turns on then off, and while it is on, it flows fuel. Say your car has 19 lb injectors, well that is measured at a specific fuel pressure, which is 40 psi for most fords. If you raised it to say, 75 psi, those same injectors will flow fuel comparable to a much larger injector for each given pulse width.
Now, onto how simple this kit is. Nitrous has pressure, lots of it. The suggested and recommended pressure is between 900 and 1050 depending on the kit manufacturer. So you have that much pressure sitting at your solenoid just waiting to shoot into your engine. Well, what if we could reduce that pressure and then put it onto the fuel pressure regulator? Well factory and most aftermarket regulators are what's called boost sensitive and vacuum sensitive. Vacuum lowering the fuel pressure(hence the line from your intake to the regulator, helps lean out the idle) and boost or pressure to the regulator increases fuel pressure pound for pound. So if your regulator saw 10 psi of pressure coming through the hose to it, it would in turn raise the fuel pressure by 10 pounds. get it? Ok, so what NOS did was make this ingenious little regulator that goes between the two solenoids in the kit. There are two solenoids in line, with a T in between them with the nitrous regulator off the T. When the nitrous is activated, the first solenoid opens, allowing the pressure to hit the closed second solenoid and the T that has the nitrous regulator on it, it steps the pressure down to about 70 to 100 psi and shoots that to your fuel pressure regulator, which raises the fuel pressure up to 70 to 100 psi, depending on the limits of your fuel system. This in turn allows a pressure switch in the fuel line, also provided in the kit, to close, and send electricity to the second solenoid that then opens and allows the nitrous to flow into the intake. What an ingenious system huh? The system won't activate until it 'sees' the fuel pressure spike up, so the engine is already starting to richen up when the nitrous arrives.
Well, how do you tune such a thing? Well, the vacuum line that goes from your intake to your fuel pressure regulator gets a T in it. Two of the legs of the T are just a straight through from the nitrous pressure regulator to the FPR, fuel pressure regulator, the other leg has a nitrous jet in it, to bleed off the pressure into the vacuum line going to the intake, so you can tune the nitrous shot, if it is too rich, then put a larger 'bleed' jet as it is called in and it will bleed more nitrous pressure off and lower the fuel pressure in the rails. Very cool huh? The opposite is also true, want more fuel to richen the mixture, then put in a smaller bleed jet. It works very well and doesn't put fuel into an intake designed to move air only. Fogger kits and Nozzle kits do a similar thing, but inject fuel and nitrous together at the entrance to the cylinder head intake port.
Now, are there other ways to do a dry kit? Yep. One of the ways is a ghetto style kit. Compucar used to make it, the bottle in a bag kit. It was very simple and kind of dangerous, but cheap so they sold a lot. The nitrous system only has one solenoid, and it passed nitrous into a nozzle that was in front of your mass air meter, and you had to 'aim' it at the sensor, so the MAF sensor would see the cold nitrous and the increased flow as the nitrous slams into the meter. This tells the computer that more air is coming in and it is very cold too, so it richens up the mixture, hopefully, and down the track you go. They only went up to 125 for a shot, but I know quite a few people that have shattered intakes and burnt plugs from these kits.
Another way to run a dry kit, is with a specific tune or system. I use a PMS and without disclosing all my race secrets here, I will shed a little light on it. the PMS is a programmable management system for the eec series of ECU's. It allows you to change many functions such as a/f ratio, injector size, timing, idle, etc. Kind of like a chip or a programmer, but in a package that is user programmable. One of the features that I utilize is the Nitrous tables. When the nitrous solenoid is activated, it takes 12 volts to turn it on, so you put a wire on that power wire going to the solenoid and send it back to the PMS and attach it to the nitrous wire provided with the unit. When 12 volts goes to the solenoid, the PMS sees that 12 volts and 'knows' the nitrous is on and active. You can then go into the nitrous tables and pull out timing and add fuel. this makes it a dry kit, and the injectors are told to open their pulse width longer by whatever value you put in. I have spent several years getting my car to function at a level competitive in the class I run in. It won't take you but a few hours on a dyno to get it dialed in and go have fun with it. This system also requires larger injectors because you are not increasing fuel pressure. So to allow the injector to be able to flow the amount of fuel required, you need a larger injector. There is a rule of thumb for that, but if you want to know, just PM me or post up.
I hope this clarifies that and I didn't mean to step on anyone's toes. I just wanted to get the knowledge out there so people can make an informed decision. I run a lot of nitrous along with a supercharged car too. Been racing nitrous cars since 1998 and my cars have been in various magazines and websites. I am a big fan of nitrous so anyone that has any questions about it are welcome to PM me or just post up on the board.
