Nitrous basics

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An introduction to nitrous oxide

There are more myths and misconceptions about nitrous than any other automotive modification on Earth.  The purpose of this document is to provide accurate information about nitrous oxide, and its use in the automotive world.  No urban myths, no tall tales, no sales pitches, just hard core technical information about nitrous, and how it works.

Terminology.  First thing is first, the lingo associated with nitrous oxide.  You’ve probably heard nitrous oxide called many things:  The juice, the squeeze, the bottle, the spray, NOS, or any host of others.  For the purposes of this document, we will refer to the chemical as nitrous oxide, nitrous, or by its chemical formula, N2O.

Why does nitrous make power?  To understand why nitrous makes power, you need to understand the basic physics behind power production.  I’ll assume that everyone that reads this knows the basics of the internal combustion engine, and the 4 stroke theory.  Power, from a physics standpoint, is created by burning gasoline.  Igniting the gasoline turns the chemical energy stored in the gas into kinetic energy that is ultimately used to move the car.  The more gasoline you burn, the more energy you release, the more power you make, and the faster the car moves.  What prevents you from burning an ultra-huge amount of gasoline to make an obscene amount of power?  Oxygen.  The only thing that limits the engines ability to burn gasoline is the amount of oxygen the engine can ingest.  With modern fuel injection you can add fuel using large injectors and a more powerful fuel pump until you literally fill the cylinders with gasoline and hydro lock the engine.  So the problem with creating power is not how to supply the cylinder with gasoline, but to supply it with oxygen.

The most obvious answer is, “Use a larger engine.”  The larger an engine is, the more air it can consume per rotation, which means it can burn more fuel per rotation, which means it is releasing more energy, and hence creating more power.  This theory is what gives rise to the popular saying, “There is no replacement for displacement.”

Another way is to increase engine efficiency.  You can change cylinder heads to aftermarket designs that flow more air, you can change the cam shaft to open the valves further and hold them open longer, use rocker arms with a more aggressive ratio, etc…  All to get more oxygen into the engine, so you can burn more gasoline, and make more power.  It’s worth mentioning here that any method of making more power that does not involve getting more oxygen into the engine, isn’t actually making more power.  Cat-back systems, for example, do not make more power.  All they do is allow the engine to push out exhaust more easily, which lets the power that was being used to push exhaust be used to push the tires.  The engine was already making that power, the power was just being used to push exhaust rather than pushing the car.  The same is true of under drive pulleys, and headers to some extent.  Those modifications do not create any power, they just allow power the engine was already making to get to the wheels instead of driving the accessories or pushing out exhaust.

Yet another method of increasing the oxygen available is to force atmospheric air into the engine at a greater rate than the engine would normally consume air.  This is sometimes called artificial aspiration, and is accomplished with a supercharger or turbocharger.  These 2 devices are basically air pumps that pump air into the engine faster than the engine would normally suck air in.  The result is more air, and hence more oxygen, inside the engine.  That extra oxygen allows you to burn more fuel, and thereby makes more power.

Finally, nitrous oxide.  Nitrous oxide is a chemical that is 33% oxygen by weight.  Atmospheric air that you, I, and our engines breathe is approximately 19.5% oxygen.  If you introduce nitrous oxide into your engine, you have added more oxygen than your engine would normally consume, and now your engine can burn more fuel to make more power. 

It’s really that simple.  More oxygen, to burn more fuel, equals more power.  All methods of power production must follow this rule.  There is no other way to make power with an internal combustion engine.

Onto the myths about nitrous.  We’ve all heard these:

Nitrous is hard on parts

Nitrous is cheating

“That one guy” blew his engine up with nitrous

Nitrous is the same as a blow torch inside your engine

Nitrous will eventually destroy your engine

You can’t run nitrous on a stock engine

Nitrous is hard on parts-  Semi-true:  Nitrous creates more power, that extra power is hard on parts.  400 HP worth of wear and tear is 400 HP worth of wear and tear.  Let’s assume you and I had the exact same engine, and they both make 300 HP.  You change the heads and the cam.  Now your engine makes 400 HP.  I add nitrous, and now also make 400 HP.  At 100% throttle, the engines are identical.  Both are burning the same amount of fuel, releasing the same energy, and creating the same power.  There is no appreciable difference in wear.  However, nitrous can be extremely hard on parts on initial engagement.  There is no other system of increasing power out there that comes on as fast and as hard as nitrous.  Using nitrous can literally double the engines power output is as little as a 200 RPM window.  That sudden hit of power can damage parts.  I would like to re-iterate though, it’s the power that nitrous creates that damages the parts, not the nitrous itself.

Nitrous is cheating-  This is a matter of opinion, and can be debated endlessly.  In this author’s opinion:  If I bust your ass at the track, it doesn’t really matter how I did it?  Not really, we left at the same time, and I covered 1,320 feet quicker than you did.  All the BS about cheating, who used nitrous, who didn’t, all that is secondary to the fact that I got there first.

“That one guy…”-  Nitrous failures are almost always due to improperly functioning nitrous systems, or driver error.  Occasionally, engine components will fail based on the load they are receiving from the extra power, but in that instance, those components would have failed regardless of how the extra power was generated.  A properly functioning nitrous system will not destroy parts any faster than anything else.  The spectacular failures seen with nitrous are usually due to fuel starvation.  As you add oxygen and leave the amount of fuel the same, the burn gets hotter.  If you were to add nitrous, but no extra fuel, the engine would not generate any more power, the nitrous oxide by itself does nothing.  All the added oxygen form the nitrous oxide would do is increase the burn temperature of the fuel that was already present.  In most cases, the added burn temperature is so great that it melts pistons, damages heads, etc…  With a properly functioning nitrous system, adding nitrous without adding fuel is impossible.  Unfortunately, many people do not use the proper safe guards to ensure that nitrous can not be introduced without adding fuel, thus leading to some of the most spectacular engine failures in the world of motor sports.

Stock engines can’t use nitrous-  Most stock engines can tolerate a small to moderate amount of nitrous use.  What ever the horse power producing limits of your stock engine, you can move to those limits with nitrous just like you could with heads and cam, a blower, or any other power adder.  For example we’ll use a 2002 LS1, from a 2002 Z28 Camaro.  The stock engine components can reliably handle approximately 450 rear wheel horse power.  That is 145 more horse power than the factory rating of 305.  Whether you add that extra 145 RWHP via supercharger, turbo, heads and cam, or nitrous oxide, the engine will tolerate the increased power with the same longevity.  Again, the sudden hit of nitrous oxide may shorten the life span of the engine, but that is typically only a problem of higher horsepower nitrous activation.  This problem can be avoided by engaging the nitrous in increments.  A 75 horse power shot, followed 2 seconds later by another 75 shot for a total of 150 in our LS1 example.

There are several advantages to nitrous:

Initial investment-  For less than $2,000 nitrous is king.  There is simply no other way to gain as much horse power per dollar.

Experimentation-  If you are considering spending $5,000-$10,000 on an engine build to create some 600 horse power monster, do yourself a favor and invest in a $500 nitrous set-up first.  Install the nitrous kit, and then go play with the car.  See if 700 RWTQ is something you really want.  Do you want the car to walk sideways when you floor it at 60 MPH?  Do you want to be forced to run slicks at the drag strip because anything resembling a street tire doesn’t stand a chance of hooking the power?  Can your drive train take the abuse of a set of slicks and 500+ horse power?  If you do decide to build the monster after you’ve played with the nitrous kit, pull the kit off, sell it on E-bay for 90% of what you paid for it, and go about your build.  If you decide that you don’t want the monster, take the kit off, sell it on E-bay for 90% of what you paid for it, and consider yourself lucky you didn’t spend 10 grand on something you didn’t even want.

Return to stock-  Removing a nitrous kit, and returning the vehicle to 100% stock is usually only a matter of a few hours in the garage.  Returning a heads/cam, supercharged, or turbocharged car to stock is considerably more difficult.

It’s only there when you want it-  Nitrous is only active when you want it to be.  You can take your stock engine out on a Saturday night, hammer on it all night long and only cause the stock amount of wear and tear on your engine and drive train.  Then, you can open the bottle and really put down some power if you want to.  With other power adders, that extra power is always there.  Every time you lay in the throttle, that extra power is there, causing that extra wear and tear on your engine and drive train.

The disadvantages of nitrous:

The empty bottle.  There’s nothing worse than lining up with an adversary, launching, and then feeling the nitrous hit go flat because the bottle ran dry.  A car with another power adder typically has the power all the time, and doesn’t have this issue.

System failure can mean engine failure-  If your fuel solenoid fails, you can destroy an engine in a hurry.  With other methods of power production, component failure does not necessarily mean engine failure, and often times there is time to back off from WOT before serious engine damage.  With nitrous the window of time between system failure and engine failure is very small when compared to other power adders, which gives the driver very little time to respond.

The stigma of being a ricer or a cheater for using nitrous-  This is a matter of opinion, and like all opinions can be debated endlessly.  I would rather win, and be called a ricer, than lose and be not be called a ricer.  That’s just my opinion though, and yours may vary.

Basic nitrous system components-

The nozzle-  This is where the action happens.  It’s the point where the nitrous and fuel is injected into the engine.  It’s usually a small threaded nozzle that you install somewhere in the intake plumbing.  They are also available in a plate that bolts between the throttle body and intake.  There are some other configurations, but these 2 are the most popular.

Jets-  These are small orifices similar to jets in a carburetor.  They install inside the nozzle, and allow you to control how much power you want to add.  They range from as little as 35 HP to 200+ HP.  These little guys are part of what makes nitrous appealing.  One day you are only adding 50 HP to the engine, 10 minutes later you can be adding 150 or more.  The ease of adding power is great, but it can be difficult to control yourself sometimes.  I recall meeting someone on the street with the 100 HP jets installed in my nozzle, but with the 200 HP jets in my pocket.  Once we agreed to race from a freeway roll, I took 2 minutes and installed the larger jets.  Truth be told, if I would have had 300 HP jets in my pocket of would have installed them.  I wanted to win so badly that I was willing to risk the entire engine.  In the end, the 200 HP shot did damage the engine in my Corvette, but the car was at least able to be driven home.  The 300 HP jets would have destroyed the engine, making it completely un-drivable.  It was an expensive lesson, so learn from my idiocy and don’t let the heat of the moment overshadow your good judgment.  The fact of the matter is that the stock engine in my Corvette would of never stood up to an additional 200 HP, whether I did it with a blower, turbo, heads, or nitrous.  I rationalized the situation to myself 100 times before installing the jets, and away I drove with a ticking time bomb under my hood.  The point of this little story is that it is incredibly easy to increase the HP output of your engine with nitrous, self restraint is paramount.

The bottle-  This is the container that holds the liquid nitrous oxide.  The bottle looks similar to a scuba tank, and is the most visible portion of the nitrous kit.  Nitrous oxide is a liquid that is sold by weight, as opposed to most liquids that are sold by volume (gallons, liters, etc…) Each bottle should have a data tag affixed to it that gives the bottles weight when empty, and the weight of the bottle when full.  When you take your empty bottle to a filling station, the fill station operator should place your bottle on a scale and add nitrous until the bottle weighs the maximum weight allowed on the data tag.  Bottles range in size from 10 ounces (about the size of the card board center of a roll of paper towels) to 20lbs (approximately the size of a scuba tank.)  There are larger bottles out there, but finding room to place such a large bottle in the car becomes a problem.

Nitrous oxide boils at approximately -190 degrees F.  That means that at any naturally occurring temperature on Earth, nitrous is a gas.  The only way to keep the nitrous in a liquid state is to keep it cooler than -190, or to keep it compressed.  Compressing the gas in the bottle, forces the the gas to remain in a liquid state.

It is important to securely mount the bottle in the car.  In the case of an accident or collision the last thing you want is a 20 lb. bottle of compressed gas flinging around inside the car with you.

All bottles have an emergency pressure relief disc.  This disc is designed to burst before the bottle bursts if the bottle pressure becomes too great.  If you mount the bottle in the passenger compartment of your car, you should run a line or blow down tube from this burst disc to outside the passenger compartment.  That way, if the disc does burst, the nitrous will vent outside the car instead of filling the cab with a gaseous cloud.

It’s worthy to note that nitrous oxide is NOT flammable.  It will not burn.  It can however, supply a huge amount of oxygen to an already burning fire.  The idea of an unmolested nitrous bottle bursting into an inferno of flame is not possible.  However, if the burst disc has been disabled somehow, it is theoretically possible for a bottle to break apart in spectacular fashion.  However, in the 5+ years I’ve been using nitrous, I have never even heard about a bottle failure.  1000’s of refills at hundreds of filling stations, and not one of the fill station operators has heard of it happening.  While it is possible, the chances are so remote that I would hardly consider the idea of a bottle blowing up in your car a deterrent to the use of nitrous.

Nitrous solenoid-  This is basically a valve that is opened and closed electronically.  It is installed in the line between the bottle and the nozzle.  When the system activates, power is supplied to the solenoid, the solenoid opens and allows nitrous to flow through the nozzle into the engine.

Fuel solenoid- Remember, when injecting nitrous into an engine, you must supply additional fuel or you won’t see any power gain.  The extra power comes from burning more gasoline, not the nitrous.  In fact, you’ll most likely damage the engine if all you do is add nitrous oxide with no additional fuel.  On carbureted engine, you normally ‘T’ the incoming fuel line just before the carburetor.  One side of the ‘T’ supplies fuel to the carburetor, the other supplies fuel to the nozzle.  The fuel solenoid is installed in the line between the ‘T’ and the nozzle.  When power is supplied to the solenoid, it opens and allows fuel to flow to the nozzle, and be injected into the engine along with the nitrous oxide.  On a fuel injected application (a C4 corvette for example) there is normally a Schrader valve and fitting on one of the fuel rails.  This valve is there so a mechanic can easily check fuel pressure, but it makes for a very convenient place to acquire fuel for the nitrous system.  Simply remove the Schrader valve from the fitting, attach a one end of a piece of braided steel line to the Schrader fitting, the other end attaches to the nitrous system.  Install the fuel solenoid inline and you’re done.

Some systems do not use a fuel solenoid.  These systems are called ‘Dry’ nitrous systems.  They are called that because they do not inject any additional fuel.  The extra fuel is supplied through the stock fuel injection system.  We’ll discuss these systems another time.

Braided steel line-  You must use braided steel line, or extremely high pressure hydraulic line for the lines in your nitrous system.  Nitrous can reach pressures exceeding 2000 PSI, so rubber vacuum line and hose clamps aren’t going to cut it.  Most industrial hose supply stores can build just about any line you need, with whatever ends on it that you need.

Arming switch-  This is the famous red button seen in all the movies.  This should arm the nitrous system.  When this switch is in the ‘ON’ position, the system is active, nitrous and fuel is flowing and you are winning the race!

That’s it.  That’s a basic nitrous system right there.  Keep in mind, that in all the above components there are no safety measures and you are trusting in the mechanical flawlessness of all the components to keep your engine alive.  You are also in direct control of when the system is activated via the arming switch.  Here’s a list of other components that are recommended by me on a scale of 1-5.  1 being nearly mandatory and 5 being almost not needed:

WOT activation switch- Priority 1-  This is a switch that mounts on the throttle linkage.  When the throttle is wide open this switch will send power to the solenoids.  This switch should only see power when the arming switch is in the “ON” position.  This allows you to arm the system before the race, and then when you go to WOT the nitrous system activates.  Engaging the system before the engine is at WOT is very dangerous, and can result in engine failure.  This switch prevents that from happening.

Fuel pressure safety switch- priority 2 – This switch has a sending unit that you plumb into a pressurized section of fuel line, or it can be placed inline between the Schrader valve and the fuel solenoid.  The switch is adjustable, so that at less than XX PSI of fuel pressure the nitrous system will not activate.  This will also shut the nitrous system down if fuel pressure drops below a set PSI.  This will help prevent you from losing an engine due to fuel starvation.  If your fuel filter is clogged, or your pump can not supply enough fuel this switch can save your engine.

Window switch- priority 2 – This switch sets the RPM’s at which the nitrous system will activate.  Spraying nitrous at too low of an RPM can cause engine failure, as can hitting the rev limiter while the nitrous is flowing.  Most people consider the minimum safe RPM for nitrous engagement 2800 or so.  I have my window switch set to engage the nitrous at 2800 RPM, and dis-engage at 5700 RPM.  That way, if I miss a shift or something, the nitrous shuts off at 5700, just before my 6,000 RPM rev-limiter.  I can also arm the system before the race, and not worry about the system engaging at too low of an RPM when I launch.

N20 pressure gauge- Priority 3-  This is a gauge that tells you the PSI in the nitrous bottle.  Proper bottle pressure is critical for nitrous system performance.  It’s not necessary if all you are looking to do is run nitrous at the occasional track event or street race, but if you’re looking for consistency, knowing the bottle pressure is a must.

Bottle warmer- priority 4- This is an electric heater used to heat the bottle.  Nitrous systems usually perform best when there is 950-1050 PSI in the bottle.  If your bottle is low, or you live in a cold climate, achieving that much PSI can be difficult without putting some heat into the bottle.  Never use a torch to heat a bottle, it can weaken the structure of the bottle, and possibly lead to bottle failure.

Bottle blanket- Priority 5- This is simply a bottle shaped blanket designed to fit over your bottle.  Once the bottle is warmed by the heater, this blanket helps maintain the pressure.

This document is not intended to be all inclusive, and should not be taken as the absolute law on nitrous oxide.  The goal of this diatribe is to hopefully dispel some myths about nitrous, and prompt you to do your own research on the subject.  If you decide that nitrous is not for you, that’s great!  You’ve made an informed decision and learned how the bottle works it’s VooDoo.

Dry Nitrous Systems

Up until a couple of years ago all nitrous kits injected nitrous and fuel through a nozzle or some other spraying device into the engine. The only problem with injecting raw fuel into a late model EFI intake is that the intake passages are designed to flow only air, the fuel is supplied near the intake port in the head with a fuel injector. When trying to flow a ‘wet’ liquid through a manifold designed to flow only air, there are a couple problems:

First, fuel fall out. Gasoline is a liquid, and as such is heavier than air. The fine mist of gasoline that is sprayed into the engine will drop towards the ground. If the fuel settles/puddles on the floor of the intake, it’s not making it into the cylinders and you risk a lean condition. This is typically only a problem of larger shots (200 HP+) when the volume of fuel is rather large.

Fuel sticking. Again, gasoline is a liquid, it tends to somewhat stick to surfaces it touches. If the fuel is flowing past barriers and other obstacles, it tends to leave those objects damp. The fuel that is staying behind to make those surfaces damp is not making it to the cylinder, and again you risk a lean condition. Again, this isn’t normally a problem until you begin to run larger shots (200 HP+). However, placing the nozzle a long ways from the throttle body can contribute to this problem as the fuel has to travel through the intake plumbing.

Distribution. EFI manifolds are designed to distribute air evenly, not fuel. If one cylinder is receiving more than its fair share of gasoline, that means another cylinder is missing some fuel, and you risk a lean condition.

You’ve probably noticed that all of these problems revolve around sending a liquid (gasoline) through an intake manifold designed to flow air. If there was a way to eliminate the liquid gasoline from the intake, you could avoid all these problems. That’s what a dry nitrous kit does. Here’s how they work:

With a dry nitrous kit, all you inject into the intake is nitrous, the extra fuel is supplied by increasing the length of time (some times called the injector pulse width) the fuel injectors are open, or increasing the fuel pressure.  There are a couple ways to increase the pulse width of the injectors.  On some mass air sensor (MAF) equipped cars, the sensor is sophisticated enough to detect the nitrous oxide, and add fuel accordingly. All that is necessary on these cars is to inject the nitrous upstream of the mass air meter, and the mass air meter takes car of the rest.  I have heard rumors of electronic devices that can interface with the factory computer and adjust the injector pulse width when the nitrous system activates. To increase fuel pressure most use a special fuel pressure regulator designed to be used with dry nitrous systems. When you activate the nitrous system, these regulators increase the fuel pressure dramatically.

The benefits of the dry nitrous system

There is no danger of fuel fall out, puddling, or fuel sticking to the manifold walls.

There is ½ the components in the system, which means there are ½ the components to fail. With a wet nitrous system, if the fuel solenoid fails to open, you could destroy the engine. With a dry kit, if the solenoid doesn’t open, you just don’t get the shot. Frustrating, but ultimately not a big deal.

Normally, dry kits are a bit easier to install. Again, there are usually less components.

I know up until this point, dry systems sound superior to wet systems, that’s not the case at all. In this authors opinion neither system is superior, they are just different. Which is best for you is up to you.

Here are some of the drawbacks of a dry system

You are depending on an electrical device to add fuel, and keep the engine alive. Mass air based dry nitrous systems have been known to not add enough fuel to keep the engine safe.

You are limited by the capacity of the injectors. If your injectors are seeing 80% duty cycle when you run naturally aspirated, then asking more of them when running on nitrous isn’t a wise decision. If you max out the injectors, you run the risk of engine failure.

Dry systems normally have a cap of about 125 HP. I have heard of people going for more power, but those stories almost always end with engine failure.

Monitoring the additional fuel is nearly impossible. You have no way of knowing if the injectors are adding a sufficient quantity of fuel. Is the mass air sensor dirty? Is your special fuel pressure regulator working properly? With a wet kit you have direct control over how much fuel you add via the fuel jet inside the nozzle. With a dry system, it’s more a ‘spray and pray’ kind of situation.

Dry systems normally engage softer. The initial hit isn’t as violent as a wet system. This can aide in reducing wheel spin when racing from a stop, or be a detriment from a freeway roll.

In any event, either system can provide years of trouble free horse power gains. Good luck, hopefully this clears up some of the mystery about nitrous, and prompts you to do your own research into a nitrous system of your own, be it dry or wet.

This document is not intended to be all inclusive, and should not be taken as the absolute law on nitrous oxide. The goal of this diatribe is to hopefully dispel some myths about nitrous, and prompt you to do your own research on the subject. If you decide that nitrous is not for you, that’s great! You’ve made an informed decision and learned how the bottle works it’s VooDoo.