Muscle Mustangs & Fast Fords
Basic Nitrous Tuning(101)
How to get the most from your nitrous combination.
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Nitrous oxide. It's the magic in a bottle that makes engines come alive and scream for mercy. Adding the juice can give your pony a 20-horsepower kick in the tail or 800-additinal stomping stallions--if you need it. The correct dose of juice can take a typical 13-second car and help it run 12s or 11s, or it can take an 8-second Mustang deep into the 7s. But before bolting a bottle to your Stang there are a few things you need to know.
First off, nitrous alone will not make your Mustang fly. Instead, it helps your engine make additional power by adding oxygen to the combustion process. Torque (and horsepower for that matter) is created by burning the air/fuel mixture efficiently in the cylinder.
When gasoline is atomized, mixed with oxygen, and burned in the combustion chamber, the result is a release of great energy and tremendous cylinder pressure that pushes down on the piston and rotates the crankshaft. And so, if you can get the engine to burn more fuel and oxygen, it can create more energy and thus more power.
To efficiently burn gasoline it takes oxygen and a spark. Only then can we complete the combustion process. While fuel is pumped in by the fuel system, the oxygen comes from the atmosphere, and therefore, it's less controllable, and that's why it is harder to pack more oxygen in the cylinders. The air we breathe is actually a mixture of 72 parts nitrogen, 23 parts oxygen and about five parts unknown gasses. But it's only the oxygen content that our engines use for combustion. If you want to get technical, we'll tell you that for every cubic foot of air, only about 21 percent is oxygen. With nitrous, the percentage of oxygen per cubic foot increases to about 50 percent. That's why some call nitrous "atmosphere in a bottle."
To make maximum power your engine needs to have the correct air/fuel ratio. If the ratio is altered due to a rich or lean mixture the engine will be less efficient. In extreme situations an excessively rich or lean condition could result in damaged parts.
Naturally aspirated street-type engines operate with approximately a 14.7:1 air/fuel ratio. However, in racing it's common to have a slightly richer air/fuel ratio, such as 13:1. When a power adder is used the ratio may be necessary to go as rich 12.5:1 or lower. That's because with power adders comes increased cylinder pressure and with that comes increased heat. And adding fuel actually keeps the combustion from getting too hot, which helps prevent detonation.
Over the years there has been great advancement in nitrous technology; however, there are still only a few different ways to deliver the spray to the engine. These systems include dry systems, wet systems, port systems and plate systems. And despite the differences between them, most kits operate similarly. A typical kit will have a nitrous bottle, fuel and nitrous lines, solenoid(s) and either nozzles or a plate to spray the nitrous and fuel into the manifold. Most kits also include some electrical connections to energize the solenoids and a switch to activate them.
With electronic fuel-injection manifolds, it is common to run a "dry" nitrous system. Having a dry system simply means no gasoline flows through the intake manifold, even though the nitrous is injected at the throttle body. In a dry system, the additional fuel is added through the fuel injectors. This is done to prevent gasoline from puddling in the manifold as it tries to turn the sharp corners found in many stock-type EFI manifolds. Puddling is very bad for two reasons: If the fuel is puddling it's not getting to the cylinders, and secondly, if a valve hangs open the fuel in the intake can explode and blow the intake right off the car.
In contrast to the dry system is the "wet" system. Wet systems inject nitrous and fuel at the same point, usually directly under the carburetor or at the throttle body on tunnel ram style intakes. Wet plate systems are very popular because they are simple and usually easy to install.
The third type of system is called direct-port. With direct-port nitrous, the nitrous and gasoline are injected by a common nozzle mounted directly into the individual ports in the intake manifold, usually at a close point to the cylinder head. A benefit to direct-port nitrous injection is the ability to fine tune individual cylinders.
Tuning For Power
Most of you know that superchargers and turbochargers add performance by pumping air into the engine under pressure. It's also common knowledge that naturally aspirated engines rely on the negative pressure created in the cylinders to draw the charge of air and gas. The beauty of nitrous oxide is that it can add power to any of these engines by adding pure oxygen to the cylinders. The difficult part of adding nitrous is tuning the flow of nitrous and fuel so the engine maintains the proper air/fuel ratio.
With today's huge electric pumps, fancy regulators and large lines, we can flood the engine with fuel if necessary. But dialing in the right amount of nitrous oxide is a bit more difficult. Fortunately, there are many levels of nitrous kits available so you don't need a degree in mechanical engineering to get going.
Using nitrous oxide is not rocket science, but there are a few basic rules to follow. By now you probably realize that nitrous has a tremendous and instant ability to produce huge power gains. Nitrous also causes cylinder pressure to rise and with that comes lots of heat. As with any power adder, excessive heat can lead to pre-ignition, detonation and severe engine damage.
So let's start with some basic rules of the game. Rule number one is, be smart. Read the instructions and follow the recommendations of the manufacturer or an experienced installer/tuner.
Second, only use the spray when the engine is in top running condition and use it in a controlled environment. If you've been driving around on a 100* day and the engine is cooking, that's a bad time to make a 20-second nitrous blast, even if it will impress your new girlfriend. Being smart also includes staying aware of your gauges and treating your car with respect.
Next, be sure to have the proper octane gasoline. The octane rating determines the gasoline's resistance to detonation or spark knock. Gasoline with a high octane rating burns (or evaporates) slower than a low-octane gas and this is absolutely necessary in the oxygen-rich environment of a nitrous engine. Our tip: if you're using a 50-125 horsepower kit, and the engine timing is set properly, you can get away with 92-94 octane gas. Beyond that we suggest using race gas.
Nitrous oxide has great power-making potential, but the "shot" or horsepower level you decided to use must be tailored to the capabilities of your engine. The nitrous user must understand that as power levels rise, the strain on the internal parts increases. Racing engines producing over 400 horsepower will require special preparation.
We all know that stock 5-liter engines can handle quite a bit of abuse, but they won't tolerate detonation very long. If you're new to the nitrous game we recommend starting with a small (50-125-horsepower) shot, and get the timing to 10* (with EFI). With carburetion back the timing off about two degrees per 50 horsepower of nitrous. Thankfully, most 5-liter and 4.6 engines can handle these smaller nitrous kits without any modifications. Still, be smart. Always run the high-octane pump gas and start with a small test squirt. Make a 300-foot run and check the plugs. If they look clean go another 300 feet. Remember, the longer you stay wide open, the larger the load on the engine. Be patient and you'll be running to the end of the track with the juice flowing. (Note: This test can also be done on a chassis dyno.)
A burned electrode on a sparkplug is a clear sign of detonation. Another sign of detonation comes in the form of black dots and a greenish tint on the plugs. A "clean" plug will show slight brownish coloration and the electrode will be in perfect condition. We also recommend that you check all the plugs, because different manifolds will distribute the fuel and nitrous differently to each cylinder and will cause some cylinders to run leaner than others. And when tuning the juice, always tune for the leanest cylinders.
In addition to learning the basic tuning procedures, it's also important to know the limit of your engine's internal components. As you increase the level of nitrous, you must also increase the strength of the engine parts. While stock rods and pistons will work with a 125-175 shot, a 250 shot normally requires stronger rod and main cap bolts, forged pistons, a stronger crankshaft, and aftermarket connecting rods.
We spoke with Brandon Switzer of Nitrous Pro-Flow and he offered a bunch of great tuning tips for the nitrous user. When it comes to carbureted combinations, Switzer likes to downsize.
"When you inject nitrous into the intake, the mist of nitrous takes up space in the intake and this can hurt the signal to the carburetor. This can also kill the velocity of the intake charge, so I recommend using a little less carburetor," Switzer explained.
Since you'll be adding nitrous, your engine will get all the oxygen it can handle. Switzer also stressed the importance of using a system purge. When you crack open the bottle on a nitrous system, the liquid nitrous flows through the line and up to the solenoid. More often than not, there will be air in the line, especially when you change bottles. By purging the system you're forcing the air to vent, as well as allowing pure nitrous to fill the line right up to the solenoid. In addition, if bottle pressure has built up beyond the recommended pressure you can vent the line to return pressure to normal. Switzer recommends between 850-950 psi. Finally, Switzer suggests purging the system and closing the bottle when you finish a run.
Having proper ignition is also a big part of the nitrous puzzle. Ignition includes the spark plugs, coil, wires, and some type of spark enhancing unit like an MSD. Stock ignition systems work well with small doses of nitrous, but we recommend a hotter ignition on larger kits. A hotter ignition will keep the mixture firing, even when cylinder pressure rises, as with a power adder.
Another trick is to close the plug gap approximately .010-inch tighter than stock. However, if you're using a high-performance ignition you can stick with the factory recommended gap setting. The danger in opening the gap too far is that the spark will fail to jump the gap, causing the cylinder to misfire. And the problem with closing the gap is that the spark can become shielded.
Another difficulty in tuning a nitrous engine is finding the optimum ignition timing. Effectively, when you move the timing you change when the spark plug fires in relation to the piston location (which is measured in crankshaft degrees). Advancing the timing causes the spark plug to fire with the piston further away from TDC and this allows the mixture more time to burn and expand, whereas retarding the timing has the exact opposite effect.
The danger in advancing the timing too much is that the result will be detonation. Anyone who has advanced the timing too much in any engine has heard the dreaded knock and ping.
Due to the high oxygen content in a nitrous engine, the mixture will burn very quickly. That's why nitrous engines require less timing advance and high-octane fuel. Switzer sets up his combinations so that the ignition timing is retarded 2.5-2.7* per every 50 horsepower of nitrous. "But you don't want to go past between 5 and 0*," he noted.
By retarding the timing past zero, the spark plugs will fire when the pistons pass TDC and this leads to excessive exhaust heat and a big loss in power. A characteristic of an engine with the timing retarded too far can be exhaust headers that glow cherry red.
Companies like MSD, Crane, Jacobs and Mallory make ignition systems that are designed for use with nitrous. MSD's Digital-6 Plus ignition box will provide a hot spark and it also has a single-stage retard built in that will automatically retard the timing when the nitrous is on. MSD also offers a Digital Multi-retard that features four stages of retard. According to MSD, "Each stage is adjustable from 0-9* of retard and a maximum of 20* can be pulled out."
As you experiment with nitrous you'll learn how the kit you select affects your engine. If your car is in the 12-13-second range, a 100-horsepower kit should lower your elapsed time by approximately one full second. If you plan on running quicker, you can build a lower-horsepower engine with lots of nitrous, or a stronger engine with a small shot. Either way, the strength of your parts should reflect the power level you plan to achieve.
There are plenty of benefits to using the giggle gas, and if properly tuned, you'll be laughing all the way to the finish line. When compared to other power adders, nitrous is relatively inexpensive initially and the bang-for-the-buck is awesome. Nitrous is also easy to install, as most kits can pump in the juice in a few hours. Additionally, you can keep the system turned off until you need the extra power, so drivability isn't compromised.
As for racing, nitrous is a great way to go really fast without spending your whole bank account. Yes, it's fun to be "jugged", as one Mustang racer put it, and that's why it's still one of the most popular ways to get your pony to giddy up.
- Bottle: Aluminum or carbon fiber cylinder used to store nitrous oxide under high pressure. Nitrous bottles range in weight from about 2.5 lbs. to 20 lbs., and typically you can get 5-6 runs from a 10-lb. bottle (with most 125-horsepower kits).
- Bottle Heater: An electrically powered device used to heat a nitrous bottle for the purpose of increasing the pressure of the stored nitrous oxide. Recommended bottle pressure is usually 850-950 psi.
- Distribution Block: A component in the nitrous or fuel system used to feed individual ports from one incoming line.
- Dry System: A type of nitrous system that feeds only nitrous through the intake manifold and not fuel. Fuel is added by the fuel injectors or secondary nozzles.
- Fogger System: A type of nitrous that offers a more precise distribution of nitrous by having individual lines that go to each port in the intake manifold. Specially designed fogger nozzles atomize the fuel mixture very well so the fuel can be more easily burned.
- Nitrous Jet (Pill): Jets, or pills as they are sometimes called, are small machined pieces resembling little arrows that offer precise control of the nitrous and fuel flow to the engine. Individual jets are placed in a nitrous or fuel line the exact flow is determined by the size of the orifice in the jet. Jets with larger holes will flow more nitrous or fuel.
- Nitrous Oxide: Nitrous oxide (N2O) is a non-toxic, clear gas comprised of two parts nitrogen and one part oxygen. When stored under pressure (such as in a nitrous bottle), nitrous is in a liquid state. However, when released from the bottle nitrous instantly changes into a gas. At approximately 572*F the bond between the nitrogen and oxygen is broken and the oxygen be used for combustion. Nitrous also cools the intake charge, sometimes by as much as 75 degrees.
- Port System: A type of nitrous system that injects nitrous oxide (or nitrous and gasoline) directly into the individual ports in the intake manifold. This type of system allows for tuning of individual cylinders, but is more complicated than plate systems.
- Plate: A device installed between the carburetor and the intake manifold (similar to a carburetor spacer) that injects nitrous and gas into the engine. A typical nitrous plate has two spray bars (one for fuel and one for nitrous) that span the opening and spray a fine mist (of fuel and nitrous) directly into the intake manifold.
- Purge: A purge system allows any buildup of air in a nitrous system to be vented from the nitrous lines just before nitrous use. This prevents any hesitation caused by excess fuel without the shot of nitrous. A purge system is recommended for all nitrous kits.
- Solenoid: A type of electrical coil that when activated acts as a valve and in turn allows nitrous or fuel to flow from the bottle to the intake manifold.
- Wet System: A type of nitrous oxide delivery system that introduces gasoline and nitrous at the carburetor or throttle body and allows the mixture to flow through the intake manifold.
|Nitrous Pro-Flow Recommended Tune-up Starting Point|
|For Carbureted Street/Strip Applications|
|Horsepower||N2O Jet/Fuel Jet||Timing Retard||Plug Heat Range|
|175||73/82||5-6*||NGK 7 or equivalent|
|225||82/91||8-10*||NGK 8 or equivalent|
|275||93/102||10-12*||NGK 9 or equivalent|
|325||102/110||12-14*||NGK 9 or equivalent|
|350+||120/116||15-18*||NGK 9-10 or equivalent|
|Bottle Pressure: 850-950 psi.|
|Recommended fuel pressure: 6-7 psi.|
|Recommended fuel: 100 octane or higher|
According to Nitrous Pro-Flow, "All engines tune differently and this is only a recommended starting point. Race engines with extremely higher efficiencies will see larger horsepower gains and may require a leaner tune-up. And secondly, a high octane-leaded racing fuel should always be used when running nitrous oxide."