Electronic Fuel Injection (EFI)

If there's one thing that's critical in a high performance engine, then it's fuel control. Think about it: the whole objective of adding a turbocharger, of installing NOS, even of installing a free flow exhaust system, is to improve fuel delivery into the combustion chamber. It is also events in the combustion chamber that can and will destroy a high performance race engine if it's not controlled properly. Here we're talking about controlling the combustion process. Now I've heard many arguments as to why sidedraft carburetors provide better performance than fuel injection and engine management, and vice versa but I always say: it's not about performance, it's about reliability and there's no better system for fuel control than electronic fuel injection. Any endurance race car from INDY Car Racing, to Formula 1, to the World Rally Championship, to the Le Mans Series uses electronic fuel injection (EFI) systems, not just for reliability but because ensuring that the correct amount of fuel is delivered under every condition, will provide the best performance.

EFI is central to engine management. It relies on an engine control unit (ECU) which processes a number of inputs from various sensors on the engine to deliver the correct amount of fuel at a particular RPM and air-flow rate/air density combination. The fuel is delivered through an injector, which is an electronically actuated solenoid valve. The amount of fuel that is delivered is dependent on the fuel pressure, which is usually a constant 30 psi above intake manifold pressure, and the pulse duration of the injector, i.e., the length of time the injector is held open.

Most EFI systems have a standard set of sensors. These include:

• The Barometric Pressure (BARO) Sensor, which provides the ECU with the atmospheric air pressure reading.
• The Engine Coolant Temperature (ECT) Sensor, which provides the ECU with the engine's current operating temperature. This is important because fuel vaporization varies for different engine temperatures. A cold engine requires more fuel while a hot engine requires less.
• The Intake Air Temperature (IAT) Sensor, which the ECU needs to take into account when determining pulse duration.
• The Mass Air Flow (MAF) Sensor, which is a tube positioned after the air filter in the air intake duct. The MAF sensor has a fine platinum wire that spans across the tube. The wire is heated by electrical current to maintain a constant temperature above ambient. The air flow past the wire cools the wire and more current is required to maintain the constant temperature. Thus, the amount of current required to maintain the constant temperature indicates the air flow rate. The air flow rate is divided by RPM to determine the pulse duration.
• The Manifold Absolute Pressure (MAP) Sensor, which uses manifold vacuum to measure engine load. An EFI system that uses a MAP sensor does not require a MAF sensor as it can use the input from the MAP sensor to determine the required pulse duration.
• The Oxygen Sensor (O₂S), which is used to measure the amount of oxygen that is not consumed during combustion. This is important for the correct operation of the catalyst converter and is used for emissions control rather than performance or economy. The O₂S is located in the exhaust system and is an after-the-fact measure of the air/fuel ratio. Too much unburnt fuel in the exhaust indicates a lean mixture while too little oxygen indicates a rich mixture.
• The Crankshaft Position (CKP) Sensor, which is important for timing purposes as it tells the ECU which spark plug to fire and which injector to open at any given point in the Otto cycle.
• The Throttle Position (TP) Sensor, which is another important sensor as the throttle position and the rate of change in the throttle position indicates the what the diver wants the car to do.

The modifications you can perform on an OEM EFI are somewhat limited because the OEM ECU is not reprogrammable. However, there are a number of things you can do to modify the EFI system without having to reprogram the ECU. You can increase the fuel pressure as this is one reading that the ECU does not take into account – it assumes the fuel pressure is a constant 30 psi above intake manifold pressure; you can intercept the pulse signal form the ECU, alter it using input from the manifold pressure and send it to the injector; you can increase the injector nozzle size; or you can increase the number of injectors. However, your best option, performance wise, is to install an aftermarket ECU. In the next few pages we'll discuss each of these options.

1 .. 2 .. 3 .. 4 .. 5 .. NEXT >

Turbochargers

The turbocharger, or a just simply the turbo, has been around now for more than a century. It was invented by Swiss engineer named Alfred Buchi in 1905 and was first used on the diesel engines of ships and locomotives from the 1920s. It was used on the engines of production airplanes from the 1930s and on truck engines from the late 1940s. But it only found its way onto the car engine of a production vehicle in 1962 when it was used on the Oldsmobile Cutlass Jetfire.

As a forced induction system, a turbo is nothing more than an air pump that is driven by the exhaust gasses of a car engine. It consists of a compressor-wheel and a turbine-wheel that are connected by a common shaft. The compressor increases the density of the air that enters the intake manifold by forcing more air into the intake manifold than what the car would normally ingest. This higher intake air density contains more air molecules and produces more power when combined with the correct amount of fuel. This is similar to the way NOS allows more fuel to be burned by providing extra Oxygen as explained by Ian. The major difference between NOS and a turbo is that the turbo provides a constant supply of extra Oxygen to the car engine while NOS only provides a limited supply.

You've got three options when it comes to turbocharging a car:

• You can simply buy an OEM turbocharged car such as a Mitsubishi Lancer Evolution, a Nissan GT-R, a Nissan 300ZX, a Nissan Silvia spec-R, a Toyota Supra, etc.
• You can buy an aftermarket turbo kit for your car engine. Here there are many options to choose from. There are Garrett turbo kits, STS turbo kits, Turbonetics turbo kits, and so much more.
• You can also build your own turbo system, which could be the best approach to car engine turbocharging as it gives you the option to build a system that meets your performance requirements and your objectives.

A complete turbo kit consists of the turbocharger as well as the necessary parts required to bolt the turbocharger onto the car engine. This includes an exhaust manifold, intake runners (plumbing to connect the turbo to the intake manifold), and can include an intercooler as well as cooling and lubrication feed lines for the turbo. When building your own turbo system, selecting the perfect turbo for a particular application can be a real challenge as no one turbo is best suited to all applications.

There are a number of things you need to consider when selecting a turbo. These include:

• The capacity of your engine.
• The number of valves.
• At what RPM to you want the turbo to come in.
• The type of fuel you plan on using.
• The turbo boost you plan on running.
• The amount of horsepower you want.

In this custom-car.us turbo guide, we'll thoroughly explain the mechanics of turbochargers and turbo systems and show you how to design and install your own turbo system. As always, the DIY route is not for everyone and if you'd rather install a turbo kit, we cover that too! For now, we'll start with the turbocharger basics ...

Turbo Basics

by "Bad Ass" Bre (December 05, 2006)

Approximately a ⅓ of the energy produced by an internal combustion engine is lost as thermal energy that is fed out the exhaust manifold. It is this energy that is used to drive a turbocharger. When the exhaust gases are forced through the turbine-wheel, the turbine-wheel becomes a reduced-flow area in the exhaust system and causes some back pressure, which causes some loss in engine power. Of course, back pressure increases as the size of the turbo decreases and inversely, back pressure decreases as the size of the turbo increases. So a larger turbo causes a smaller loss in power, but it also requires more air-flow, and hence more RPM, to spin up or spool up and produce boost pressure (i.e. above-atmospheric pressure). This is referred to as turbo lag. So a larger turbo produces less back pressure but has more turbo lag while a smaller turbo produces more back pressure but has less turbo lag. So what is better? The answer to that depends on what you're looking for — low-end torque, top-end power, or a bit of both.

A Garret Turbocharger

TURBO LAG

Later on in the series we'll look at turbo sizes, but for now, let's get back to turbo lag. Turbo lag is defined as the time between the point when you hit the accelerator and the point at which the turbo produces enough boost to create boost pressure. This may sound like a bad thing but what would happen if you didn't have a turbo? You'd get no boost! So it's either no turbo lag or no boost. A simple choice, I think, especially when you consider that the loss of power due to back pressure caused by the turbine-wheel is hardly noticeable. Provided you haven't done something silly like lower your compression ratio! In years gone by car manufacturers built production turbo motors with low compression ratios to counter the thermodynamic effect of compressing air. Any time air is compressed, the temperature of the air increases. This affects the internal combustion temperatures in the engine. But when a suitable intercooler is used to cool the intake air, normal compression ratios can be used. With normal compression ratios, you're still getting close to normal aspirated performance until you get boost and then you're flying with an up to 50% increase in bhp, depending on the boost you're running! But let's not get too excited just yet, we'll go back turbo boost first.

BOOST PRESSURE

We've said that turbo lag is the time between the point when you hit the accelerator and the point at which the turbo produces enough boost to create above-atmospheric pressure in the intake manifold. The boost level at which the turbo produces enough boost to create above-atmospheric pressure in the intake manifold is called the boost threshold. This is the point at which the exhaust gas flow over the turbine is high enough to overcome inertia and spin the turbine-wheel fast enough so that the compressor-wheel can begin creating boost pressure. From that point on boost will increase but it is important to remember that the quality of the fuel you run and the temperature of the air pumped into the intake manifold will influence the amount of boost you can run. With normal pump fuel, a stock engine and an intercooler, you can safely run at 7-12 psi boost. A wastegate regulates the boost pressure by allowing exhaust gases to pass around the turbine-wheel so as to limit the exhaust gas flow that drives the turbine-wheel.

But more about wastegates at a later stage; here's something to ponder on for now: A properly installed and tuned turbo operating at 10 psi can reduce the 0-60 mph time by a third, despite turbo lag! Yes, you read right a 10 second car will do 6.66 seconds if the turbo is done right!

There are a number of factors, such as turbo lag, boost threshold, heat, back-pressure, low-end torque, and top-end power, that you must take into account when selecting a turbo. A large turbo will suffer from turbo lag and won't produce much low-end torque but it also won't put too much heat to the intake charge, won't have much back-pressure, and will produce loads of top-end power. A small turbo, on the other hand, won't have much turbo lag and will produce loads of low-end torque but will also have lots of back-pressure and will add lots of heat to the intake charge. You can't have the best of both worlds but you can select the best turbo to suit your needs.

Deciding which turbocharger best suits your needs in a bit complicated. You need to know what your objectives are — street car, a purpose built ¼ miler, a race car, or a rally sprint car. Once you know what you want, you should have a better idea of at what rev range you want your power band to be. Once you know that, then it becomes easier as you can select a compressor-wheel to match your rev range.

SELECTING THE COMPRESSOR WHEEL

The compressor-wheel is most efficient at a particular boost pressure or pressure ratio (PR) and air flow (cfm). At this point the turbo will put the least amount of heat into the intake charge; anywhere else, including at lower boost pressures or revs, it will put more heat into the intake charge. The idea id that the point of efficiency should coincide with your most useful rev range. So it's a matter of determining the bore diameter of the compressor wheel that is most efficient at your most useful rev range; and by most efficient, I mean at least 60% efficient. Each compressor-wheel has a compressor map that maps efficiency at various pressure ratios and air flow rates but you need to calculate the air flow rate for your engine. You can use the following formula to calculate the air flow rate:

PR × CC × ½RPM × VE

In this formula, PR is the Pressure Ratio. This is the absolute pressure produced by the turbo divided by atmospheric pressure. Atmospheric pressure is 14.7 psi at sea level. If you're running 7 psi of boost, your absolute boost pressure is 21,7 psi (7 psi + atmospheric pressure). This will give you a PR of 1,47 (21,7 ÷ 14,7), which means that approximately 47% more air/fuel mixture is being forced into each cylinder.

We halve the RPM because a four stroke internal combustion engine requires two revolutions to complete one power cycle

CC is engine capacity but in cubic feet and not in cubic inches. Why cubic feet? Because cfm is cubic feet per minute. You can convert engine capacity to cubic feet by dividing cubic inches by 1728.

VE is volumetric efficiency. This is the total amount of air/fuel mixture that each cylinder ingests during the intake stroke and is expressed as a percentage of the actual volume of the cylinder. You can calculate the VE as follows:

2 × mass airflow rate
air density × swept volume × RPM

Yes, I know, it's getting a bit complicated! Fortunately we can use a rule of thumb that states that modern engines have a VE of 80-90% while older engines like the Datsun L-series engine have a VE of 60-70%!

SELECTING THE TURBINE WHEEL

The turbine-wheel uses exhaust gas energy to spin the compressor-wheel fast enough to produce the required air flow rates at the desired boost pressure. A larger turbine-wheel will produce more power to spin the compressor-wheel at the required air flow rates, although s smaller turbine-wheel will spin faster. A smaller turbine-wheel will also offer greater restriction to the exhaust gas flow, causing back pressure between the turbine-wheel and the combustion chamber. So the basic size of the turbine wheel will be determined by the air flow required from the compressor-wheel. The important element here is the extruder bore size, i.e., the inner diameter of the turbine outlet. An extruder bore with a 2 inch diameter will be sufficient for a compressor-wheel air flow of 250 cfm to 400 cfm; an extruder bore with a 2½ inch diameter will be sufficient for a compressor-wheel air flow of 400 cfm to 500 cfm; an extruder bore with a 2¾ inch diameter will be sufficient for a compressor-wheel air flow of 500 cfm to 600 cfm; an extruder bore with a 2⅞ inch diameter will be sufficient for a compressor-wheel air flow of 600 cfm to 800 cfm; and an extruder bore with a 3 inch diameter will be sufficient for a compressor-wheel air flow of over 700 cfm.

CONSIDERING THE A/R RATIO

The A/R ratio is another important consideration in choosing the turbine-wheel. The A/R ratio is the ratio between the cross-sectional area (A) of the turbine scroll at any one point and the distance or radius (R) from that point to the center of the turbine-wheel. This ratio is always constant so each point along the turbine scroll will have the same A/R ratio. A turbo with a smaller A/R ratio will tend to create more torque while a turbo with a larger A/R ratio will provide more power because more exhaust gas energy will be acting on the turbine-wheel. Generally, an A/R ratio of 0.7 will provide better low-end response, while an A/R ratio of 1.4 will provide more top-end power.

Installing a Nitrous Oxide System (NOS)

Installing a NOS kit is a simple process of installing the nitrous tank; a few injectors (which are also called nozzles); and a few solenoids; routing a few meters of tubing (or piping) from the nitrous tank and a fuel line to the solenoids, and the solenoids to the injectors; and then fitting a few switches to arm the electrical circuit that energizes the solenoids. If you are installing a Dry System, you don't need to run a pipe from your fuel line to the fuel solenoid as you don't need to install a fuel solenoid but you will need to modify your EFI system to provide the correct amount of fuel when you engage your NOS system. In my experience, the best way to install the nitrous system is to install the nitrous tank first, followed by the injectors and the solenoids, then connect your feed lines, and connect your solenoids to the battery. This will ensure that each of its elements correctly placed to operate at their full potential. If you are installing a Wet System, you must test the system and ensure that the fuel pressure to your fuel solenoid is constant and adequate. This may require that you install a high pressure fuel pump and/or a fuel regulator.

Begin by installing the NOS tank. The correct installation of the tank is important to getting the most out of your nitrous system. As we've mentioned in our basic nitrous system guide, the NOS tank has a siphon tube that extends from the release valve to the bottom of the tank. The siphon tube reaches the side of the tank on the opposite side of the label. Therefore the tank should be installed at a 15° angle, with the label facing up and the release valve facing the front of the vehicle. This will ensure that more of the liquid N₂O is used before the siphon tube begins to pick up gaseous Nitrous Oxide, even under acceleration.

Another consideration is the pressure of the NOS tank. The pressure of the NOS tank will fluctuate as the ambient temperature fluctuates. This can cause problems with the correct calibration of your air/fuel mixture. To overcome this problem, you should ensure that the NOS tank is mounted away from heat sources (such as the exhaust system) and out of direct sunlight. You can also use a NOS blanket to insulate the tank.

You should install the injectors next. The placement of the injectors will depend on whether you're installing a system with a single injector, or a Direct Port System that requires one injector per cylinder. When you need just one injector, you should install the injector as close to the throttle body as possible. If you have a rubber inlet hose connected to your throttle body, you must drill a suitably sized hole to fit the injector, and bolt the injector down with a nut and washer on either side of the hose. If you have a cast aluminum manifold, you must drill a hole and tap a thread into the cast aluminum for the injector to screw into. If you are fitting a Direct Port System, make sure that everything that must be fitted to the intake manifold is in place and find enough space on the manifold to fit the injectors. The injectors must be fitted at the same distance from the cylinder head but try not to fit the injectors too close to the cylinder head. Also, wherever you fit the injectors, apply a little locktight to the thread to ensure that the injector does not work itself loose. If you are installing a Direct Port System, you would need to install a distribution block between the solenoids and the injectors. The purpose of the distribution block is to distribute the fuel and nitrous between the injectors. Although it is not crucial, try to install the distribution block so that the tubes are more or less horizontal. The injectors for a Wet System has two inlets — one for fuel and the other for nitrous. You must connect the right tube to each inlet as indicated on the injector.

The next step is to install the solenoids. These should be installed away from the exhaust manifold but as close to the nitrous injectors as possible. The solenoids must also be installed slightly higher than the injectors to ensure that the nitrous and fuel do not need to flow upward as this will reduce the effectiveness of the system. The solenoids are electrically operated; therefore you'll need to run a few electrical cables to the solenoids.

Once you have your hardware in place, you can install the nitrous and fuel supply lines. It is best to route the tubing that carries the nitrous to the engine bay along the stock fuel line as this would be routed securely, and away from heat sources. The tubing should be secured to the vehicle so that it cannot be damaged by abrasion or by moving suspension and drive train parts. You can use nylon tie-wraps to secure the tubing to the vehicle but ½ inch Tinnerman clamps work much better. The tie-wraps or clamps should be placed no further than 18 inches apart. Whenever you route the tube trough a metal body panel, be user to use suitably sized rubber grommets to prevent the body work from cutting through the tube.

If you are using nylon tubing, you can use a sharp utility knife to cut the tube to the correct length leaving about 2 inches of free play at either end for possible flexing. Never cut the tubing too short and never cut the tube using a scissors or wire snips as this will deform the tube and make fitting the olive and nut quite difficult. Once you have cut the tube to the correct length, slide the nut over the tube with the treaded part facing the end of the tube. Never tighten the nut too much as this will cause the olive to compress the tube and will restrict flow through the tube. Then slide the olive over the tube. Secure the nut to the outlet on the NOS tank while keeping the tube in place and repeat the process at the other end where you must secure the nut to the inlet on the nitrous solenoid. The tube from the solenoid to the injector will require the same treatment. You can install the tube from the fuel solenoid to the injector as well but don't secure the tubing to the fittings on injector just yet — you will need to perform a few tests first. Also beware, the injector for a Wet System has two inlets — one for fuel and the other for nitrous. You must connect the right tube to each inlet as indicated on the injector. Next, tap into your fuel line using a metal T or Y splitter and fit the tubing that will supply fuel to the fuel solenoid and connect it to the inlet on the fuel solenoid.

The final step is to install the electrical circuit that will power the solenoids. The NOS solenoid must lift the plunger against the pressure that can be upwards of 800 psi in the system. A fair amount of current (amps) is required to accomplish this task so make sure that the electrical cables can supply the required amperage to lift the plunger. The electrical circuit should supply both solenoids with power and should incorporate a fuse, a microswitch fitted to the accelerator linkage, an arming switch and a relay. Start by disconnecting the negative terminal from the battery. This will prevent you from causing short circuits while working on the electrical system. Run a live wire from the positive terminal of the battery to the fuse box under the dashboard and on to a relay. Another live wire can then be run from the relay to the relay to the solenoids. This wire must carry sufficient current to activate both solenoids. You can fit the arming switch on the live wire between the relay and the solenoids as this wire will run close to the dashboard area; however it is better to place the switches on the earth wire. The earth wire will run from the solenoids to a suitable metal point on the vehicle's body but it is best to run the earth wire to the negative terminal on the battery. You can fit the microswitch to the earth wire as the solenoids would be placed close to the accelerator linkage.

There you have it, you're done. All that's left now is to test the nitrous system and ensure that the pressure to your fuel solenoid adequate, and then tune the nitrous system for best performance.

Testing and Tuning Nitrous Injection Systems

by "Bad Ass" Bre (February 03, 2007)

TESTING NOS SYSTEMS

Once you have your nitrous system installed, you must test the system to ensure adequate nitrous and fuel flow. This will ensure proper performance and reliability.

Start by ensuring that the fuel line is properly attached to the fuel solenoid and turn the fuel pump on. You can do this by turning the ignition key to the ACC position. Check for fuel leaks where you tapped into the stock fuel line and where the fuel line feeds into the fuel solenoid. Cure any fuel leaks, check again for fuel leaks and then disconnect the fuel line from the nitrous injector. Activate the system and check for fuel flow when the system is activated, and that the fuel stops flowing when you deactivate the system. If you don't get fuel flow, check that the fuel solenoid is operating properly — you should hear an audible click when the solenoid is activated; check that you have fuel flow at the fuel filter; and ensure that fuel line is not kinked, twisted or bent. If you do have fuel flow, turn the vehicle's ignition off and properly secure the fuel line to the nitrous injector.

Now open the release valve on the nitrous tank check for frost along the nitrous feed line. The frost will indicate a nitrous leak. If you find any leaks, close the release valve on the nitrous tank and cure the leaks. Open the release valve again and ensure that you've cured all nitrous leaks. Then disconnect the nitrous line from the nitrous injector. Activate the system and check for liquid nitrous flow when the system is activated, and that the nitrous stops flowing when you deactivate the system. If you don't get nitrous flow, check that the nitrous solenoid is operating properly; and ensure that nitrous line is not kinked, twisted or bent. If you do have nitrous flow, you can properly secure the nitrous line to the nitrous injector.

TUNING NOS SYSTEMS

Nitrous tuning is another simple procedure but you should first tune your engine without nitrous as you will be running without nitrous for most of the time. Tuning the nitrous system is quite straight forward — you start with the jet sizes recommended by the manufacturer of your nitrous system and gradually adjust the jet sizes until the air/fuel mixture added by the nitrous system is perfect.

So install the jet sizes recommended by the manufacturer of your nitrous system. This will be conservative and will err on the rich size (i.e., too much fuel), which is the safe side to err on. Run you engine for a while with the nitrous activated and then check each of your spark plugs to determine how the air/fuel mixture is burning. The correct air/fuel mixture will produce a brownish, grayish-tan color on the spark plugs. If the spark plugs have a sooty, black color, your air/fuel mixture is too rich and you should increase the nitrous jet to the next jet size. If the metal part of the spark plugs displays a bluish or rainbow coloration, go to a smaller nitrous jet size immediately. Repeat this test until your spark plugs display the correct color. Never jump up by more than one jet size on the nitrous side and never try to work your way down from a lean mixture — that's just looking for trouble and major engine damage. You can make more power by increasing the fuel jet size and then adjusting the nitrous jet size up until your spark plugs display the correct color again.

WARNING: Back off as soon as you get detonation and reduce the size of your nitrous jet!

You may also need to adjust your ignition timing as nitrous oxide makes the air/fuel mixture burn much faster than normal. Retard the ignition timing by 2° increments (i.e., less advance before TDC) until you feel a noticeable loss of power. Then advance the ignition timing by 2°.

Now that that's done, your nitrous system is installed, tested and tuned; all that's left is for you to enjoy responsibly — always enjoy power responsibly!

NOS Basics and Layout

The basic nitrous oxide injection system, or a NOS kit, is pretty straight forward and easy to grasp. It consists of a nitrous oxide tank, some tubing, a nitrous solenoid, a fuel solenoid and toggle switch, throttle position microswitch, jets, a nitrous fogger, a relay, nylon pipe, and a distribution block.

The nitrous tank is used to store Nitrous Oxide in a liquid form. The tank is actually a pressurized canister as Nitrous Oxide must be compressed to remain liquid at room temperature. Remember N₂O reaches boiling point (i.e., it becomes gaseous) at -127° F and more Nitrous Oxide can be stored when it is in a liquid form. Approximately 850 psi of pressure is required to keep Nitrous Oxide liquid at room temperature and at sea level but the nitrous tank must be pressure tested and certified to withstand 1,800 psi. If the certification on your NOS tank is older than five years, your nitrous dealer will not refill it and you will have to have the tank pressure tested and recertified. The tank is mounted in the car's trunk and has a siphon tube that is connected to the release valve and extends to the bottom of the tank. The tank must be mounted at a 15° angle to ensure that the maximum amount of Nitrous Oxide can be released from the tank.

High pressure nylon or Teflon inner-lined braided-steel pipe is used to carry the Nitrous Oxide to the engine where it is regulated by the NOS solenoid. The solenoid is an electrically controlled valve which uses a strong electromagnetic field to open a small plunger the blocks the flow of the liquid Nitrous Oxide. A second solenoid is used to supply extra fuel so that the air/fuel mixture remains constant. Both solenoids are controlled by electric switches that activate the electromagnetic field. The NOS system should have at least two switches — a microswitch that is fitted to the accelerator linkage and is only activated at full throttle; and a spring-loaded momentary switch that is activated by the driver. The microswitch on the accelerator linkage ensures that the nitrous system can only be activated at full throttle. Activating the system during part throttle or during a gear change can have very catastrophic consequences. As an added precaution, the oil pressure switch can also be used to ensure that the system can only be activated when the engine is running and there is oil pressure. Starting an engine with NOS in the combustion chamber can also be very catastrophic.

Some more high pressure nylon or Teflon inner-lined braided-steel pipe is used carry the nitrous and fuel (which are still separate at this stage) to the intake manifold where it is released into the engine via two small jets that are located in a special nitrous injector. The jets must be correctly calibrated to release the correct amount of fuel for a given amount of nitrous. In addition, the pressure on the fuel supply side must be adequate and at a constant level to ensure that the air/fuel mixture is correct at all times. This may require the fitting of an electric fuel pump and a fuel regulator.

The quantity of the nitrous flow depends on the size of the jet fitted. A jet is basically a screw with a whole through it. It's used as a restriction tool depending on the size of the link up orifice. Applying a bigger jet is the easiest way to squeeze a bit more power out of your current system. The fuel supply comes from a similar jetting system.

There you have it — the basics behind NOS systems and NOS kits. In our next section we'll look in more detail at NOS installation ...

An Introduction to Nitrous Oxide (N2O) Injection

Anyone for some NOS?

Nitrous Oxide (N₂O), or NOS as it is commonly referred to, is a quick and easy performance boost for any motor vehicle, regardless of whether it's a car, a bike, a boat or a plane. In technical terms, Nitrous Oxide is a chemical compound that consists of two Nitrogen atoms and one Oxygen atom. However, Nitrous Oxide does not occur naturally as a chemical compound but has to manufactured by applying heat and a catalyst to nitrogen and oxygen compunds. Nitrous Oxide was first discovered by the British chemist, Joseph Priestly, in 1772 but it wasn't until 1942 that Nitors Oxide was first injected inon an internal combustion engine to boost the power output from the engine. Nitrous Oxide is not combustible and is in liquid form when under pressure. When it is released into the combustion chamber the pressure is removed and the Nitrous Oxide becomes gaseous, releasing extra Oxygen that allows your engine to burn more fuel during the combustion process. At the same time, the chemical process of changing from a liquid into a gas absorbs lots of the heat from inside the combustion chamber, reducing the chances of detonation and pre-ignition. NOS thus provides an instant but relatively safe performance boost.

The major advantage of NOS is that it is relatively cheap when compared to all the other forms of car modification and the amount of work involved to install a full nitrous system is far less than that of installing high performance cam shafts, turbochargers or superchargers. The only drawback is that you must refill your Nitrous Oxide tank. Nitrous Oxide is stored in a pressurized tank to keep it in a liquid state. Unfortunately, Nitrous Oxide refills are not as freely unavailable as gasoline and must be purchased from an authorized dealer. The relative low cost of installing a NOS system makes it an ideal power boost project for anyone who can read and understand a little simple physics. As with anything in life, if you don't do it right, you're going to get problems. There is also more to installing NOS than just bolting a NOS tank to your trunk and connecting a long tube to your engine. The bottle has to be mounted at a 15° angle to ensure that the last of the gas is used and none is wasted. The plumbing is also very intricate and can be very tricky to a first time NOS installer.

None the less, in this custom-car.us NOS guide, we will explain the physics of nitrous oxide injection and show you how to install a NOS kit and how to test and tune NOS.

There are three different types of nitrous oxide systems that you can implement:

• The Dry System, which is the NOS system in which no fuel is sent to the intake charge outside the vehicle's normal means.
• The Wet System, which is the NOS system in which fuel and nitrous oxide are supplied through a fogger and then sprayed through the throttle body.
• The Direct Port System, which is a Wet System in which each engine cylinder has its own fogger.

We'll cover all of these over the next few pages. Now let us start with some NOS basics ...

WARNING: NOS causes an extreme increase in fuel combustion; therefore, any problem in your engine can turn out to be 10 times worse with nitrous installed!