Why Nitrous?

Nitrous oxide--the name alone sounds cool. And while the movies glamorize it and make it seem like some out-of-this-world mystery gas, you should know nitrous is not that fancy. In actuality, the magic is noting more than two of the Earth's elements--nitrogen and oxygen. Engines rely on a mixture of oxygen and a fuel (such as gasoline) ignited by a spark to make combustion and power. And nitrous simply provides your engine with copious amounts of oxygen. The result greatly enhances the combustion process and massive gains in horsepower can result.

The bang-for-the-buck comes from the fact nitrous kits are relatively inexpensive, they are simple in design, easy to install, and pack the potential to drastically increase the horsepower output of your engine with the push of a button. Additionally, nitrous systems can be turned on or off, making them perfect for street/strip applications.

In the past we've covered nitrous installs where we've picked up 80-150 hp, sometimes with an even greater improvement in torque. We've lopped a full second or more from our quarter-mile times, and done it without sacrificing driveability. But nitrous has its own evils. We're sure you've heard the horror stories. What we've learned, however, is many of the mishaps come from nitrous misuse. More often than not, the biggest problem with nitrous comes from users who lack an understanding of the product and those who get greedy and go after the biggest shot they can find. In actuality, this is the same as the guy who buys a supercharger and tries to run 16 pounds of boost on 89-octane fuel or without the proper tune-up.

This article will educate you on the topic of nitrous oxide. We'll expose some common mistakes and offer some tuning tips to help you get the best performance from your nitrous system.

Engine Basics
Before we can bolt up a bottle and extract extra power, it's important to understand how your engine produces that power. Simply grasping this theory will help you understand why adding nitrous increases the output.

Stated in basic terms, the internal combustion engine is a mechanical device designed to harness and apply the power produced from the combustion of fuel and oxygen. Alone an engine can not make power, but with the proper ratio of fuel (gasoline or other), oxygen and a spark, the internal combustion engine can generate torque and horsepower. Some of the smallest engines make as little as a 1/2 hp, while Top Fuel engines that burn nitromethane can make upwards of 8,000 hp.

Engines work by ingesting the mixture air through the induction system. The air is mixed with a fuel by a carburetor or fuel injection system and fed to the cylinders. Pistons then compress the mixture of air and gas into the combustion chamber. At a predetermined point during the crankshaft rotation (usually just before the pistons reach TDC) the air/fuel mixture is ignited by a spark plug. If the engine is tuned properly the mixture burns rapidly and energy is released in the form of heat.

It's important to note that the mixture does not explode, instead it burns rapidly. As the mixture burns the gasses expand, the pressure in the cylinder rises, and force is applied to the pistons (and rods). Thus, it is simply the cylinder pressure that forces the pistons down to rotate the crankshaft. The crankshaft, in turn, transfers the energy from combustion into a rotating force. We call this rotating force torque. Through this simplified example you can see more cylinder pressure equals more power at the crank.

And one way to raise cylinder pressure is to burn more fuel because burning more fuel should create more heat, right? Yes, to a degree. You can't simply dump extra fuel in and expect good results because engines rely on having the proper air/fuel ratio to run efficiently. Generally, the air/fuel ratio will fall between 12:1 and 14.7:1 (air to fuel). Simply adding more fuel to an engine (without increasing airflow) will cause a rich condition and that kills power. The key is to add more fuel and also more oxygen.

We can feed an engine more fuel by raising the fuel pressure, enlarging the injector size or by commanding the computer (in EFI applications) to do so, however, increasing the airflow is not always simple. Racers and hobbyists often install larger carburetors, ported intakes, heads and larger camshafts to increase airflow, while others bolt on a supercharger or turbocharger, which forces compressed air into the engine. In contrast, nitrous oxide boosts power only by increasing the oxygen content available to the engine and then by matching the oxygen with additional fuel we see increased power. That's why nitrous has been termed "atmosphere in a bottle."

Nitrous is stored in the bottle and is fed through a line to a solenoid, usually located near the engine. When the solenoid is energized nitrous flows to the engine and is injected either near the throttle body, under the carburetor by a plate system or directly into the ports in the intake manifold. Additional fuel is either supplied by the injectors, or by supplemental lines connected to a solenoid that activates in sync with the nitrous solenoid.

Nitrous: What Is It?
Nitrous oxide (N20) is a cryogenic gas composed of nitrogen and oxygen molecules. At roughly 570-degrees F the oxygen molecule separates from the nitrogen molecules and the oxygen becomes available for combustion. In other words, nitrous artificially crams more oxygen into the combustion chamber of an internal combustion engine. Nothing more, nothing less.

Nitrous oxide is so efficient because it has a higher percentage of oxygen per cubic foot than even the atmosphere does. The atmosphere that we live in is comprised of about 20 percent oxygen and 80 percent nitrogen, where nitrous is 36 percent oxygen and 66 percent nitrogen. In lay terms, this means nitrous contains over two times as much oxygen per cubic foot.

Yet another plus is that nitrous has a cooling effect. Unlike our atmosphere, nitrous is injected from a pressurized bottle. And when the pressurized nitrous leaves the bottle it changes from its liquid state (in the bottle) to a gas (when it's sprayed into the engine). During this process it absorbs heat and the effect reduces the temperature of the nitrous to approximately 127-degrees below zero. We know horsepower is normally increased by about 1 percent for every 10-degree drop in inlet air charge temperature and nitrous can drop the inlet temperature by 50-70 degrees.

Nitrous exists in two grades, U.S.P. and Nitrous Plus. U.S.P. is the medical grade and commonly used as a mild anesthesia, especially in dentistry. U.S.P. is not available to the public. Nitrous Plus differs only in the fact that it contains small amounts of sulfur dioxide to prevent substance abuse.

Nitrous Tuning
Okay, you've purchased your nitrous kit, installed it, and you're ready to play. You expect to go faster, but here are a few things you should know. Before you crack open the bottle and hit the button, we recommend you read the instructions not once, but twice. Almost all the kits sold today offer basic starting points for jetting and timing, as well as some additional tuning tips. And according to the pros, one of the biggest mistakes people make is not following instructions.

That said, let's get to some tuning. As we stated earlier, the theory is to add nitrous and additional fuel and then burn the mixture efficiently. Maintaining the proper air/fuel is critical in a nitrous engine because the additional oxygen can cause a lean condition in a hurry. The good news is that the nitrous companies have done the homework for you and if you stick to the recommended settings, you'll stay within a safe margin.

All the experts we spoke to agreed that nitrous newcomers should stick to the manufacturers recommendations. However, you should also realize that many basic kits are designed for stock applications and modified engines will require a different tune-up.

"It's important to know that every engine is different so each combination will have a different baseline tune-up," says nitrous guru Steve Johnson of Edelbrock (and formerly of NOS). "Naturally, you'll be reading the spark plugs and one mistake people make is trying to tune the engine based off of one plug. Read them all. Different plugs and different fuel will leave different trace marks so I recommend sticking with one fuel and one type of plug. Generally, I can look at the ground strap and see the bluish coloration."

If the strap is getting too much heat the whole thing may be blue, however, if the strap is very thick, or very thin the readings will differ. "The bluish tint normally relates to the timing advance," Johnson continued. "I believe the old rule of timing retard vs. level of nitrous is skewed because it really depends on the engine combination and the cylinder heads. Generally, the more efficient the head, the more timing needs to be removed.

Both Johnson and Brandon Switzer of Nitrous Pro Flow agree bottle pressure plays a big role in any nitrous tune-up. "My recommendation is that you should tune your engine to a single bottle pressure. Heating the bottle raises the bottle pressure and has a great effect on the flow and how much nitrous will get to the engine," says Switzer.

"One of the most important items to have in any nitrous system is a pressure gauge," added Johnson. "If you have varied pressure, you will not maintain consistency and if the pressure gets high, like more than 25 psi above your normal setting, you run the risk of having a lean condition and that can tear stuff up." Johnson recommended running with between 900-950 psi.

NMRA Drag Radial-champion Chris Little was also kind enough to offer up some helpful advice. "I generally go by the rule that you take out 2 1/2 degrees of timing for every 50 hp of nitrous. At the track I look at the weather conditions and then tune accordingly. I don't really mess with the jets, but I'll adjust the timing based on the weather. In cool weather you need to take out more timing than in hot humid air. When it's humid, there's water in the air and you can't burn water. The water actually cools the mixture so you can keep more timing in there."

Little speaks from experience, as his '90 LX has been as quick as 8.46 at 160-plus mph. It's powered by a 406 built by Bennett Racing and wears TFS High Port heads, a Wilson-prepped intake and a BG 1,000-cfm carb. Internals include aluminum rods, 13.5:1 pistons and a Comp Cams camshaft.

"When it comes to tuning nitrous I have to say that avoiding detonation is the key. I use VP 121 octane gas and I run the same fuel pressure all the time. Some people make mistakes by having the timing too high and not having enough fuel, but you can hurt an engine by doing the opposite, even though you think too much fuel and too little timing is safe.

"Every nitrous user should have a magnifying glass to read plugs and they should check the plugs at the end of the run, not after you drive back to the pits. My plugs look totally different when I click it at the end of a run and in the pits, after I've driven back," Little added. "Always go with plugs that are two heat ranges colder than stock because sometimes stock plugs will melt down even if the engine is not lean. A clean plug should have some bluish coloration on the strap, but not be totally blue. Note the shape of the electrode when new. Then look at it after a run. The electrode tip should retain its square shape and not be rounded off. Lastly, the porcelain should be discolored with a brownish or yellowish tint. Not totally white, but not totally brown either, and it should not have any specks on there. Specks that look like glitter could be bits from aluminum pistons and that mean detonation."

Like most automotive topics, nitrous is one that could fill a book--and it has, many times over. This article was designed to offer the basics in regards to operation, theory and tuning. We hope you learned a bit and can now put your newly found nitrous knowledge into practice.