Nitrous oxide has a lengthy history in the world of hot rodding, but our collective understanding of this performance-enhancing chemical compound still leaves something to be desired. Comprised of two nitrogen atoms bonded to one oxygen atom, N₂O injects additional horsepower into an engine by essentially creating a larger combustion event than air and gasoline are able to generate without it.

“The air we breathe is 21% oxygen, but in nitrous oxide, it’s 36% oxygen,” notes Doug Wright of Holley Performance. “Oxygen is what makes combustion happen in an internal combustion engine, and with roughly 12% more oxygen by volume in the mix, you’re able to create a bigger boom. And that bigger boom translates to more power.”

Shop NOS nitrous oxide kits here.

This naturally begs the question: Why don’t we just use pure oxygen to create an even bigger boom, then? As Wright explains, it’s basically a situation where too much of a good thing creates more problems than it solves.

“Engineers had that same thought back in the day, but what they discovered is that pure oxygen is very volatile. This makes combustion unpredictable and very hard to control. So that’s where nitrogen comes into play – it’s very stable until it reaches temperatures exceeding 565 degrees Fahrenheit. At that point it’s already in the combustion chamber and you’ve generated the heat you’ve expected to generate in the combustion process. And that means you don’t have the risk of that detonation happening at an earlier stage without that increase in temperature, which is something you’d otherwise have to contend with when using pure oxygen.”

But in order to fully realize the benefits of nitrous oxide in a performance application, foundational knowledge is crucial. With that in mind, we sat down with Wright to get all the details.

ML: Generally speaking, how does the cost of a nitrous setup compare to other power adders like superchargers and turbos?

DW: Nitrous oxide is widely known as the “power per dollar” champion of the performance world. It’s one of the least expensive ways to introduce big increases in power. With a supercharger or a turbocharger setup, you’re typically looking at upwards of $5,000 when all is said and done, whereas you could get a 150 horsepower increase with nitrous for much less than $2,000 – probably closer to $1,000. It’s tough to beat from a cost-effectiveness standpoint.”

ML: Can nitrous be safely used with any type of engine, or does it require specific types of engine components?

DW: There are different levels of nitrous that you can use to generate different levels of power. Ultimately it just comes down to the fact that an increase in oxygen requires an increase in fuel to support it. So, the key factor is whether your fuel system can deliver enough fuel to accommodate that additional oxygen in the engine. But assuming you’re using an appropriate level of nitrous for the application, it can be safely used in stock engines without other major modifications.

Nitrous gets a bad rap for being unsafe, but those kinds of issues generally come down to folks not addressing the needs of the system. Fuel delivery is very important, as well as ignition timing adjustments. It definitely changes the dynamics of the combustion process, but as long as you accommodate those changes, it can be used very safely and effectively.

ML: What kind of power increases could you potentially see from a stock GM LS V8? What about a Honda B-Series?

DW: With stock LS, you could easily add 150 to 200 horsepower without much effort. With a B-Series, you could do power shots starting around 35 horsepower up to 50 very safely.

ML: OK, now let’s discuss some of the core elements of nitrous system design. What’s the difference between a “dry” nitrous system and a “wet” nitrous system?

DW: With a dry nitrous system, you have a nozzle exclusively injecting nitrous oxide into the engine. It’s mixing with fuel coming from a separate delivery mechanism in the air intake. With a wet nitrous system, in addition to introducing nitrous into the system, it’s also introducing its own supply of additional fuel into the intake. Since nitrous involves higher levels of fuel being delivered, you can either do that with a pre-existing fuel delivery mechanism, most commonly and increase in fuel injector volume – which is how a dry system operates – or you can introduce that additional fuel as an integral part of the nitrous oxide system via a nozzle with inlets for both fuel and nitrous, which is how a wet system functions.

Shop NOS nitrous nozzles here.

ML: Let's take a look at a few of the common types of nitrous system designs. Can you explain what a carburetor-plate system is, the kinds of applications it’s designed for, and how much this type of system typically costs?

DW: If you have a carbureted application, this is the most common way of implementing a nitrous system. With this design, a plate sits in between the carburetor and the intake, and it injects both fuel and nitrous into the system as the air is being funneled into the manifold. (NOS Crosshair Professional Kit plate for 4250 carb, shown at left) The only other way you’d implement a nitrous system in a carbureted setup would be with a direct port design, where you’d be putting a port with both fuel and nitrous oxide into each individual cylinder. While that’s certainly doable, and you get a lot more consistency in the amount of nitrous that’s being introduced per cylinder, it’s a much more complex setup and more costly. A carburetor-plate system is much simpler by comparison, and less expensive in turn. You could easily do a plate system for less than $1,000.

Shop NOS carburetor plates systems here.

ML: Turning our attention to fuel-injected applications, how does an EFI direct port fogger system compare to an EFI throttle body plate system in terms of design and cost?

DW: With a direct-port fogger system, individual nozzles spray nitrous and fuel into each cylinder or intake runner. Like the direct port systems for carbureted applications, this design gives you the ability to deliver precisely measured amounts of nitrous to each cylinder, but it’s a fairly complex design and it typically involves tapping the intake manifold. These setups usually cost between $1,000 and $1,500.

Shop NOS direct-port nitrous systems here.

With an EFI throttle body plate system, instead of having to thread nozzles into the intake, a plate is installed in between the throttle body and the air intake, and that plate would have injection points plumbed into it already for fuel and nitrous delivery. So, it’s a very straight-forward install, and they’re usually less expensive than a direct port fogger system. A system for a GM LS with a 10lbs bottle, for example, can be had for less than $700.

Shop NOS throttle body plate systems here.

ML: What additional components are needed to make a nitrous system fully functional?

DW: Solenoids are a key part of the system; they drive the physical delivery of the fuel and nitrous, and you have individual solenoids for each of those. Originally these solenoids were activated by pushing a button, while microswitches are mechanical devices that are triggered by pedal position to ensure that nitrous is only introduced at wide open throttle.

But as we talked about earlier, the technology has come a long way in recent years. With Holley EFI systems, our engine management software in the HP, Dominator, Terminator X, and some Sniper and Terminator X systems allows you to manage your nitrous system through the ECU so you can dial in exactly when and how much you want the nitrous to be used. You obviously don’t want to introduce nitrous unless you’re under wide open throttle, and you don’t want to introduce nitrous until your engine is up to speed. The software gives you the ability to do things like set limiters that prevent it from engaging below 3,000 RPM and disengage at 300 RPM before the rev limiter. All of that can be done at the system level instead of relying on the driver to apply the nitrous at the optimum points.

ML: How does jetting affect the operation of a nitrous system?

DW: Jetting controls the amount of nitrous that you’re putting through the system. You have different jet sizes you can use, and the size of the orifice is going to determine whether you’re applying a 50-horsepower shot or a 250-horsepower shot, for example.

One of the key things to keep in mind if you’re doing a jetting change is that you have to make sure your air/fuel ratio and your ignition timing are correct for the new jetting size. Any time you’re going to adjust the amount of nitrous that’s being used, you want to make sure that you’re adjusting the tune accordingly. And that’s why having a wideband gauge that can keep tabs on the AFR is also important.

Shop NOS individual flare and funnel style jets and jet kits here.

ML: What other factors must be considered in order to optimize a nitrous system?

DW: Any amount of nitrous introduced into the engine is going to change – and increase the temperature of – the combustion process. So typically, you want to run spark plugs that are one step colder in order to accommodate that. Ignition timing must also be adjusted any time nitrous is being introduced into the engine. And while it’s common to run nitrous on standard pump gas, an octane booster can come in handy if you, for example, have your vehicle tuned for 93 octane and you find yourself in a situation where you only have access to 91 octane.

Bottle pressure has a significant impact on the efficiency of the nitrous system as well. Colder temperatures equate to lower pressure, and because this is a pressurized system, you can easily gain 50 horsepower with a bottle that’s running at the appropriate temperature versus a cold bottle that’s under-pressurized because it’s below the optimum temperature range. That’s why we recommend using a bottle heater.

A purge kit is also very helpful to have. Over time, air will build up in the lines of the nitrous system, and without a means of purging that air, it can lead to a delay in the nitrous being delivered to the engine as that air works its way through the system. That can result in a lag of power, and the vehicle will run rich when that happens because the engine is getting all of the fuel to accommodate the nitrous, but the nitrous isn’t actually being delivered yet. A purge kit is basically a blow-off valve that removes the air from the system and primes the lines with fresh nitrous, so it’s ready to go ahead of being activated.

ML: How long does a typical 10 pound. bottle of nitrous last, and how much does it cost to refill a bottle of that size?

DW: You should be able to get about 10 quarter-mile passes out of a 10-pound bottle, depending on how big of a shot you’re running. 10 pounds is generally considered the sweet spot in terms of sizing, but you can go all the way up to a 20-pound bottle, or all the way down to two pounds. With larger bottles, weight and physical size become limitations. In terms of cost, it’s about $150 to refill a 10-pound bottle.

ML: Any other advice you’d offer to folks who’re just getting started with nitrous systems?

DW: The first thing that springs to mind is that we hear a lot of scary stories about people using blow torches to increase the temperature of the nitrous bottle. Don’t do this, it’s extremely dangerous.

Also be aware that the bottle’s orientation in the vehicle will affect its performance. At its resting state, nitrous oxide is a liquid inside of the bottle. There’s a tube in the bottle that pulls the liquid nitrogen out to feed the line, and that tube is positioned to pull from the lowest point in the bottle when the bottle is tilted slightly upward with the label facing up. So you want to orient the bottle so that the label is facing up at an angle and that bottom section of the bottle is pointed toward the rear of the vehicle.

It’s important to orient it this way because, as the vehicle is accelerating, the g-forces are going to push that liquid rearward, and this orientation will ensure that the tube will still be able to pick up that liquid as it’s being pushed downwards in the bottle. The instructions included with our NOS bottles will show you how to do this properly. Following the instructions is a good rule of thumb for nitrous systems in general. When used correctly, these systems can be game changers.