Created By:	Posted be ricerxs Written by Mike Robinson	Category:	Engine
Date Posted:	02-21-02	Views:	4887
Title:	NOS setup, what's safe and not
Article:	Mike, after reading this post I had to display it. This is the best article I have read on NOS and I felt this should have definatly been displayed. OK.... I'll straighten out the confusion assosiated with NOS kits. There are several different types of NOS systems avaliable. A "dry manifold" system injects nitrous in front of the throttle body and then increases fuel pressure at the rail to add more fuel. A "wet manifold" system utilizes foggers or spray bars (both of which combine nitrous and fuel and spray the mixture). A direct port sytem has a fogger for each cylinder, usually located close to the head in the intake runners. The spray bars are commonly found in plates sandwiched behind or under a carb or throttle body. Nitrous is pretty violent stuff, causing cylinder pressures that can get excessive when too much is used. Therefore, it's best to get the same amount of nitrous to each cylinder. If the cylinders are off, and the differences get too great, the stress on the engine will usually toss a rod or snap the crank in two. If a nitrous goes lean, the oxygen rich mixtures will melt pistons in the blink of an eye. Now that I've got everyone afraid of nitrous (it's a tool just like fire and you can get burned.....), I'll explain a few things. Air flows differently than fuel vapor. Air can turn a sharp corner, but fuel vapor will "shear" and can't turn as fast without seperating. An enclosed space full of fuel vapor and a spark or worse yet an explosion is a bad idea. When you use a wet manifold sytem on an engine with a dry manifold, you can get the above circumstances within your intake manifold. Fuel will puddle in the plenum, and a backfire could turn an intake manifold into a bomb. If you install a single fogger in front of a throttle body on an EFI car (a TBI system is wet manifold, so that case is ok), you get what Kurt Gordan likes to call a "Blow- up Kit." When you use foggers down in the intake runners near the fuel injectors, it's safe, because you won't get a build up of fuel vapor in the plenum. Another thing to note is that nitrous injects into an engine at 800-900 psi. If you have a dry manifold kit injecting nitrous right in front of the throttle body, it has a tendancy to "pile up" at the end of the intake manifold. What this means is that a 50 hp dry manifold kit is really adding uneven amounts of nitrous to the cylinders. For example, 20 hp in cylinder 1, 15 in cylinder 2, 10 in cylinder 3, and 5 in cylinder 4. That's a difference of 15 hp between cylinders 1 and 4. It also means that all of the cylinders need to be rich enough to keep cylinder 1 from going lean. This type of kit puts more stress on the engine, and it's not recommended to go above 50 hp on a 4 cyl engine with a dry manifold kit. However, testing has shown that 50 hp can be used this way without adversely effecting engine wear or reliability. 6 cylinder can take 75-100 hp, and a V8 can take 100-150 hp dry manifold. The biggest advantage of the kit is ease of installation. You can spend $380 for a new dry manifold system, install it yourself in a day, and all of a sudden a 140 hp Isuzu 1.8 has 190 hp with the push of a button. When it's off, the car drives like normal. 50 hp is usually enough for a 1 to 1.5 second decrease in 1/4 mile times on a light car. A direct port system is harder to install and usually runs $550. You need to remove the intake manifold and you need to route fuel to each fogger. Expect the setup to take much longer and the tuning to be more difficult (jet changes are easier at the throttle body than under an intake manifold and you've now got 8 jets instead of 1 or two) However, the dry manifold system was adding 20 hp to cylinder 1. If you added 20 hp to all cylinders, the engine runs smoother and therefore more reliably. That means that you can safely run 80 hp of nitrous direct port, where you could only run 50 dry manifold. Said storm with 140 hp now has 220, the same power as a turbo Impulse maxed out on boost. And while it has less traction, it's also lighter. If you want to go above 80 hp of nitrous, you'll need better rods. And if you want to go up to 150 hp, you'll need to drop $4000 into the engine just to make it strong enough to hold together. 150 hp of nitrous might as well be a 28 psi turbo. A couple other points..... An engine with forced induction will respond very well to nitrous, as the cooling effect of -200+ degree nitrous does wonders for intake temps at high boost levels. An AWD Impulse has some beefy rods, and I'd love to see an Impulse turbo re-boosted to 18 psi and running an 80 shot of nitrous. Expect to blow a few head gaskets unless proper steps are taken, though..... (like O-ringing) Also, nitrous is generally not a good idea at low rpms or at high rpms when a fuel cut kicks in. I would highly recommend an RPM switch to control the RPM range of the nitrous. Features that come with the kit include a fuel pressure switch (if fuel pressure drops the nitrous turns off) and a throttle switch (you should only use it at full throttle). You can also get other goodies like bottle heaters (to maintain bottle pressure at set levels) and remote turn-on valves (don't have to pull over and pop the trunk so you can turn on the bottle. Another goodie is a nitrous controller. You can get progressive controllers which will make a 4 banger feel like a V6 (brings the nitrous on according to throttle position). Or you an get controllers that bring the nitrous on in a curve. This allows you to add nitrous as you get traction, and helps reduce driveline stress. Another method would be to stage the nitrous, adding say 50 hp off the line and then 100 more hp once you hit third gear. Kurt Gordan's Civic is running a 150 shot direct port, and has a custom spray bar where the secondary butterflies used to be that adds another 75 hp in third gear. He's managed mid 11's using only nitrous. Nitrous can be an excellent hp adder, and is one of the most cost effective mods you can get. However, bottles tend to go fast (about 10 14 second bursts at 50 hp), and you should expect to pay $25-35 and in some cases as high as $60 for a refill. If you want a very streetable car, but occasionally want that little boost of power for racing once in a while, then nitrous is an excellent choice. If you want power all the time, you'd be better off with other mods. Any questions? Any errors? Mike Robinson 1991 Isuzu (with said $4000 in mods to allow 150 hp of nitrous) Stylus XS