So You Want To Use Nitrous Oxide Without Blowing Up Your Engine

by Matt Brown


Nitrous oxide has a bad rap, and the reason it has a bad rap is the same reason it is so great: it’s easy. Too easy; for about $500 and a few hours of work, you can add basically any amount of power you want. If you are a reasonable person with self-control and a nitrous controller, you can add 35 horsepower to your Ford Mustang and be totally content. This is, of course, a fictional situation because nobody who drives a Mustang has that kind of self-control. In fact, most gearheads don’t think this way. I know this because when I added 25 horsepower to my engine, literally all of my friends had the same question: “Why only 25?”

Because I don’t want to scatter a trail of oil and connecting rod pieces down the pavement like some sort of junkyard Johnny Appleseed. Because I sat down, looked in the mirror, and said, “Twenty-five is enough. I am not going to succumb to the almost overwhelming urge to go with just a little bit bigger jet size.”

Later, of course, I installed the 35 horsepower jets, proud of myself that I resisted the urge to go all the way to 50.

This lack of self-control is a common reason why nitrous oxide gets the unfair reputation. Also to blame: installations that result in an improper oxygen/fuel mixture, and too much nitrous oxide at the wrong RPM. How to avoid these failures? Use a wet system, install a nitrous controller, and don’t go overboard with the added power.


Wet Systems

There are two types of nitrous systems: wet and dry. Dry systems are great if you’re adding a very small amount of power or if you don’t really care if your pistons melt. Nitrous oxide is an oxidizer, and you need to add fuel with the added oxygen to get power. The mixture of fuel and oxygen needs to be pretty close to ideal so that the mixture can ignite at the right time and the right temperature. Dry nitrous systems do not add that fuel and expect the engine to do it automatically. A dry nitrous setup is you saying “I’m just gonna make my engine go WAYYY lean and let the ECU figure out what to do with that.” Yes, modern engines will compensate up to a point, but that point depends on the altitude, air temperature, O2 sensor quality, a ton of other things, varies from car to car, and won’t actually compensate very much. 
There are some dry systems that can add more nitrous to the mix. They work by having the fuel injectors add more fuel, either through programming additional fuel in the map when the system is on or adding additional injectors controlled by some sort of magic box. Another way to provide some enriching fuel is by doing something like raising the fuel pressure while the nitrous is on. These dry systems can tolerate a little more nitrous.
Two solenoids: one for nitrous, one for fuel. This is the correct number of solenoids. Also acceptable is 4, 6, or 8. Never 1.

Wet systems add extra fuel with the oxygen in the appropriate ratio (assuming you set up the jets correctly). This is the same as you saying “Here you go engine; here’s 50 extra horsepower in a neat little package.”

The kit (or the internet) should tell you what combination of jets to use for the desired power, but you should use a wideband oxygen sensor to verify that the jets are giving you the air/fuel ratio you are looking for. Generally, you want to have the same ratio with nitrous oxide as you have without.

If you are running a fuel injection system, it may automatically fix your slightly incorrect jet pairing. It will also add more fuel to compensate for the colder air; part of the power increase from nitrous oxide comes from the colder, denser air you get when nitrous oxide changes from a liquid to a gas. This phenomenon was the inspiration for the hit 70's funk band “Latent Heat, And The Vaporizations.”

Okay, that last sentence is not true.


Nitrous controller

The next key to not exploding your shit is a nitrous controller. A controller will look at your RPMs, your throttle position, and hopefully your fuel pressure, and will only activate the nitrous oxide when these parameters line up in the don’t-explode-the-engine column. They also do other things, depending on how much money you spend, like measure nitrous pressure, boost, and vehicle speed, and progressively add nitrous oxide instead of just dumping max horsepower at once. (If you’re thinking about using a multi-stage system, you might be better off getting a fancy controller that will pulse width modulate the solenoids and give you a much better ramp in; the controllers these days are pretty great.) You may not need some of these features, but you definitely need something that will keep the solenoids from opening when you’re at low RPMs, are not at full throttle, or don’t have fuel pressure.


You can actually accomplish the basics without a nitrous controller if you use an RPM window switch and have dummy switches for wide open throttle and fuel pressure wired in series.

It is important to measure fuel pressure because you’ll go super lean if you keep spraying nitrous oxide when fuel flow decreases. This could happen if you’re low on fuel and it sloshes away from the pickup, or if you tied your wet system into your existing fuel pump and you’ve just reached the flow limit of that system.


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J. Michel
J. Michellink
Wednesday, December 13, 2017 5:09 AM
my stock ford sigma engine pumped up crank 55hp using a 35hp "chart combination" on 100% alcohol. That was the most scariest day in my life. rs
Boxed Fox
Boxed Foxlink
Wednesday, December 13, 2017 5:51 PM
I love the writing style and your humorous novella-like method of dissuading people from doing dumb shit with their cars. By any chance, you don't happen to be the same Matt Brown that authored "Racecar: Searching for the Limit in Formula SAE" would you?
Matt Brown
Matt Brownlink
Wednesday, December 13, 2017 8:02 PM
Thanks Boxed Fox! And yes, the very same :)
Boxed Fox
Boxed Foxlink
Wednesday, December 13, 2017 9:01 PM
Oh that's brilliant! You know your book is actually my favorite racing-related read?

Sometimes I'll get into a rut about how hard / expensive / painful racing is and start wondering if I should be doing something more sensible with my life. When that happens I crack open "Racecar", laugh my ass off, and fondly reminisce about my own college days skipping parties to work on my friends' cars in the many parking lots on campus. By the time I'm done all I want to do is to stay up all night to wrench on the car and do whatever it takes to put on a good show at the next race. It's an awesome story. Thank you for sharing it.

Looks like I'll be checking MotoIQ more often now.

Thursday, December 14, 2017 8:28 AM
My buddy M. Pederson knows you as SuperFastMatt..... so when are we going to hear about that?
Sunday, December 17, 2017 2:03 AM
Hi there, candid question. Say i could program my ECU (as in change the code running it in), it has some spare I/Os, and my job is actually about doing that kind of stuff.

Could i use a "dry" nitrous system and setup my ECU with a dual mapping system that would activate when nitrous is used ? This would result in a "programmable wet" system. I like to go KISS , so i'd rather have my ECU change injector duty and timing itself than wiring a second set of somewhat "passive" injectors with that dual solenoid system. The question is, could it work ?

(I'd also like to program a nitrous controler function in that ECU but there is not enough MIPS in there)

Matt Brown
Matt Brownlink
Sunday, December 17, 2017 10:40 AM
That would work as long as the fuel system can handle the increased flow. I'd still add fuel pressure monitoring if that isn't already in the ECU.
Monday, December 18, 2017 2:31 AM
Thanks. Nitrous is not popular at all where i live, so it is hard to find any info. Is there a rule of thumb about the fuel quantity that needs to be added per nitrous used, so i could somewhat size the injector need ? What you are saying makes me feel the fuel demand increase is big and sudden, so maybe a single fuel line might not be enough. I guess it explains why wet systems are sold, and not what i want to do.

I am running a 1.8L turbo engine, and will push up to 38lbs of boost in it so fuel pressure will go quite high. I was thinking of using nitrous to cover for turbo lag and inject again when power is needed. I feel like i could cover the spool help with a simple system and small jets, but the "power adder" version would need bigger jets and possibly a secondary fueling system with its own pump and FPR...
Friday, January 05, 2018 1:40 AM
This is REALLY badly written as people regularly throw 1000+hp of nitrous pretty safely into motors in drag racing
usually with a dry system
article needed to say this was more pointed at home diy idiots
nitrous doesnt blow shit up
dumb people do
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