Nitrous stuff

Motor photos
MiataPower Dir
Nitrous Oxide


Page one deals with the basics in nitrous oxide.

Page two deals with all the different stuff and gadgets that goes into this.

Page three deals with common questions and calculations.

Page four deals with installation of a dry single fogger system.


There are basically two different ways that you can get the nitrous (and fuel if it's a wet system) into the intake manifold. Either you use nozzles (see below) or you use an injection plate. A plate is usually placed under the carburator or behind the throttle body.

These are mostly used on V8's but are available for others also, but not the Miata though.


A nozzle is used to inject the nitrous (and fuel if it's a wet system). The nozzles below are wet system nozzles. The left one is the FOGGER2 and the right one is the new Annular fogger. I don't use either of these (they didn't have a picture of the type I use) but instead a type called Soft-Plume, which gives a more cloud like injection. The two below have a fairly directed injection.


The picture below shows different nozzles, different types of jets and how to connect them to different tubes.


The bottle brackets are used to hold the nitrous bottle in place. The pair to the right is quite expensive! They also have a new type that looks like a mix of these two but with a fast release mechanism, very cool.


The microswitch is mounted at the throttle body and is used to trigger the nitrous system at wide open throttle (WOT). In the picture to the right you see it installed on my car.


There are two types of pressure switches, the ones that open at a certain pressure (break the circuit) and the ones that close when a certain pressure is reached.

The close-type pressure switch is used in both wet and dry nitrous systems. In wet systems it breaks the circuit (disables the system) if the fuel pressure drops below a preset value. In dry systems where the extra fuel is added by increasing the fuel pressure, the switch is used to close the circuit and inject the nitrous when the correct fuel pressure is reached.


A fuel pressure regulator has two uses, first it keeps the fuel pressure constant (very important with nitrous) and it also lets you set the pressure to what you want (well, at least downward). There is a good reason to use a lower fuel pressure with a wet nitrous system, it allows you to run bigger fuel jets, which means that there is less chance of the jets clogging up. I use the type in the left picture, the one on the right is a more expensive race version.





A normal nitrous kit for the Miata usually comes with jets for 50hp, that's a good point to start with and the stock Miata fuel pump will be enough. If you want to go higher I suggests an A/F ratio gauge and a fuel pressure gauge. To change horsepower and/or fuel mixture you change the bypass jet (located in the T between the manifold and fuel pressure regulator) and nitrous jet (located in the nitrous injector).


The stock Miata ignition is just fine. I recommend using NGK BKR6E-11 extended reach spark plugs gapped to 0.028". They have worked great for me. When it comes to timing, I have tried 14, 16 and 18 degrees with good result (I'm running 11 right now since I have the turbo also). A J&S knock sensor is a good investment since you don't want detonation under any circumstances and especially not with nitrous since it generates fairly high cylinder pressures. The problem with knock sensors is that nitrous completely changes the way the engine sounds (the exhaust note as well as the engine noise), that makes reading the J&S tricky.


Nitrous and fuel pressure gauges

An Air/Fuel mixture gauge is a must in my opinion! I use the Link A/F gauge from DlrAlt. The nitrous pressure varies depending on the temperature and if you are right on the spot a normal day, you WILL be running lean on a hot day, not a good thing! This is in my opinion the only weak point in a nitrous system. Keep an eye on that A/F ratio!

A N2O pressure gauge to mount permanently in the cockpit is a good investment if you are serious about this, unfortunately I don't have one yet! Both Autometer and NOS sell good ones (actually, the NOS gauge IS the Autometer with a different dial face).

A fuel pressure gauge in the cockpit is a must if you are aiming for higher horsepower. It will tell you everything you need to know about the fuel delivery (very important).


Old style bottle heater

The purpose of a bottle heater is to keep the nitrous bottle warm, duh!
The pressure of the nitrous (and therefore the air/fuel ratio) is depending on the temperature of the nitrous. The trick to keeping the air/fuel ratio consistent (which is the key to making good power and staying out of trouble) is to keep the temperature consistent. The biggest weakness of a nitrous system is the temperature dependence and a bottle heater goes a long way of solving that. It isn't perfect since it doesn't cool the bottle when it gets too hot, but it's much better than nothing. The picture above is NOS's old heater.

NitrousExpress have a bottle heater that regulates the heat based on the nitrous pressure. The NOS guys said that there are several problems with that 1) The NitrousExpress kit measures the pressure after the bottle valve, if you close the bottle valve and forget the heater on, BOOM! 2) When you start heating the bottle, the pressure will rise quickly without the whole bottle being warm. When you then open the solenoid the excess pressure blows out and you are left with the pressure that your cold nitrous can produce. The NOS bottle heater measures the temperature of the bottle instead. The kit they had before wasn't any good because 1) The heater element was too small, it sometimes took 20 minutes to get a bottle up to 84 from 60 Fahr. 2) The temp sensor wasn't any good, it would sometimes not record the temperature of the bottle correctly making the heater heat it too much. A new one that solves these issues is already designed but at the time of this writing there was problems with a sub-contractor.

If you have a bottle heater, it's a good thing to have a bottle blanket (shown below). It keeps the bottle temperature more stable and makes life a little easier for the heater.

Bottle blanket



Remote bottle valve

NOS sells something that is called a Remote Bottle Valve (shown above). It's an electronically controlled on/off valve (a solenoid) that is mounted on the bottle after the manual valve and can be operated from the cockpit to turn the nitrous on or off in the system. I don't know if the NOS guys are being overly cautious but they say that you still have to close the manual bottle valve when you leave it for a longer time (like overnight). The remote bottle valve will let some pressure through even when it's closed and if you have a leaking solenoid seal, you WILL know about it when you start the engine! If you close the bottle during the night or make sure your seals are in good condition, I don't think you would have any problem with the remote bottle valve. I once got a little nitrous in the manifold when I was working on it and when I started the engine 15 minutes later it went to redline 0.01 seconds after the first ignition!!!!!

The last time I talked about this problem with NOS they suggested a T-valve instead (shown below). It has several advantages over the remote bottle valve, 1) it's much cheaper. 2) you can mount it inside the cockpit within each reach. 3) it's a 100% blocking seal when you turn it off, no leakage what so ever.




Purge valve

A purge valve can be use for two things. When the system is pressurized (valves open but the solenoid is closed), the nitrous in the line closest to the solenoid starts to turn in to gas instead of liquid. The primary usage of a purge valve is to let that gas out so you'll have liquid at the solenoid. The other thing you can use it for is to let the pressure out of the system after you've closed the valves, thereby releasing the pressure on the solenoid and extending its life.


Last revised: Friday, February 02, 2007