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.

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Designing and Building an Exhaust System

The main purpose of an exhaust system is undoubtedly to route the bunt air/fuel mixture out of the car's engine. Along the way it may be used to drive a turbocharger and now-a-days it will most definitely incorporate a catalyst converter to reduce carbon dioxide emissions. But on a high performance car, such as a modified street car, or a modified race car, the exhaust system does much more than that as it also affects engine performance and engine tuning!

An exhaust system generally consists of an exhaust manifold (which is also called an exhaust header), a front pipe, a catalyst converter, a main muffler or silencer, and a tail pipe. Of these items, the muffler is the easiest to deal with — simply replace the stock muffler with a performance muffler, such as a Flowmaster muffler, to create a free flow exhaust system. However, the performance muffler must have an inlet and an outlet that is the same size (diameter) as your front pipe and your tail pipe. Your front pipe and your tail pipe should be the same size. The rest of the exhaust system is complicated by questions of back pressure, your engine's power band, and your engine's maximum usable RPM.

BACK PRESSURE

Back pressure is an important consideration because too much back pressure will adversely affect top-end engine performance as it will restrict the flow rate of the exhaust gasses at high RPM. The car's engine will not be able to expel the burnt air/fuel mixture at the required rate. The burnt air/fuel mixture remaining in the cylinder at the next intake stroke will contaminate the fresh air/fuel mixture and will rob the engine of power. Thus, fitting a 1 inch pea-shooter to your engine in place of the exhaust pipe is not a good idea! But then neither is fitting a 10 inch sewage pipe. If the exhaust pipe is too large, you will get reduced flow velocity of the exhaust gasses. The flow velocity of the exhaust gasses assists with the scavenging of the exhaust fumes as well as the amount of air/fuel mixture that can be drawn into the combustion chamber on the next intake stroke. This is because the flow velocity of the exhaust creates a low pressure immediately behind it that sucks more gasses out of the combustion chamber.

BASIC DESIGN

Generally speaking, when designing an exhaust system for a 4-cylinder engine, a 2¼ inch exhaust pipe is ideal but for a 6-cylinder engine, a 2½ inch pipe is ideal, though a 2000cc 4-cylinder race engine could do with a 3 inch exhaust pipe. The size of the exhaust header primary pipes of also influences back pressure and flow velocity, while the length of the primary pipes affect the power band of your engine. The size and length of the primary pipes and your exhaust header design depends on your engine's power band, displacement and maximum usable RPM.

The Exhaust Header

As I've mentioned in our introduction to exhaust systems, the exhaust manifold design, or exhaust header design can have a major affect on engine performance. The primary pipe diameter and primary pipe length of the exhaust header has a significant affect on the engine's power band and peak power. When design the exhaust header, you need to take into account the number of cylinders, the engine capacity, and the maximum usable RPM.

NORMALLY ASPIRATED STREET CAR

When designing the exhaust header, remember that a 1600cc 4-cylinder or 2400cc 6-cylinder normally aspirated street racer with a maximum usable RPM of 5,500 should have a header with a primary pipe diameter of about 1½ inch and a primary pipe length of 34-36 inches, while a 2000cc 4-cylinder normally aspirated race engine should have a header with a primary pipe diameter of about 1¾ inch and a primary pipe length of about 32 inches that feeds into a 2½ inch collector. The primary pipe lengths should be within 2 inches of each other and all four primary pipes on a 4-cylinder should join together in a single collector before feeding into the exhaust pipe. A 6-cylinder engine should have two collectors with cylinders 1, 2, and 3 joining into one collector and cylinders 4, 5, and 6 joining into the other collector. A Y-pipe could then be used to join the two collectors before feeding into the exhaust pipe.

ALL ROUND RACE PERFORMANCE

For all round race performance, a header with 1⅝ inch primaries that are 32 inches in length usually provides the best power curve over the widest RPM range. Shorter primary pipes provide better low-end torque while longer primary pipes provide better top-end power but at the expense of acceleration. On a turbo engine, a header with short primary pipes will help with acceleration until boost pressure is reached and the turbo kicks in.

ANTI-REVERSION

Each primary pipe should at least match the exhaust port diameter or should be slightly larger. A primary pipe that is slightly larger than the exhaust port is better as it inhibits reversion, which is the flow of exhaust gasses back into the combustion chamber when the downward movement of the piston creates a vacuum in the cylinder. The exhaust valve is still open when the intake stroke begins. Preventing reversion will reduce the contamination of the air/fuel mixture by exhaust fumes. An anti-reversion (AR) header that is designed to inhibit reversion would be your best choice. AR headers have a built-in lip that restrict exhaust gas flow back into the cylinder.

Ultimately, determining the correct primary pipe diameter and primary length that provides the best engine characteristics and performance will require that you have your car dyno-tuned.

Turbo Exhaust Systems

The same rules regarding the exhaust header design that apply to normally aspirated engines also apply to turbo engines but with a few rather significant twists.

An exhaust header with equal length primary pipes that joint together in a collector is always better than a log-type header in which short primary pipes branch into a thicker log pipe. However, on a turbo engine, space limitations may necessitate the use of a log-type header. In addition, the primary pipes of the header will be determined by the size of the turbine inlet.

A major twist in the header design of a turbo exhaust system is the integration of the wastegate. The wastegate is used to control boost pressure and to prevent over boosting. For this reason, the wastegate should be integrated into the header so that it is exposed to as much of the pressure in the exhaust as possible. This means that the wastegate should be located at or after the collector where all the primary pipes join together, or after the last exhaust port on a log-type header. Also, the wastegate should be located at an angle that does not restrict exhaust gas flow. The exhaust gas must be able to flow to the wastegate so that the wastegate can experience the correct exhaust pressure in the system.

There are also a few important aspects of a turbo engine that you must take into account with regards to your tail pipe. Firstly, the turbo increases the amount of air/fuel mixture that is fed into the combustion chamber and consequently increases the amount of exhaust gas that must be expelled from the engine. Secondly, the exhaust gasses of the turbo engine are much higher than a normally aspirated engine; therefore the exhaust on a turbo engine will be more prone to heat expansion. The flange that is attached to the turbine outlet can experience temperatures of up to 1500°F! For this reason the flange should be beefed up and a minimum flange thickness off a ½ inch with additional bracing is recommended. The rest of the exhaust system needs to make allowance for heat expansion and should incorporate swaged joints

The size of the tailpipe is also complicated by the size of your turbo and the boost you are running. Some tuners recommend a tail pipe that is 10% larger than the turbine outlet. This takes turbo size into account but not boost pressure! I personally prefer basing my tail pipe size on the bhp produced by the engine. As with normally aspirated cars, arriving at the ideal tail pipe diameter, as well as the ideal primary pipe diameter and length, will require some time on the dyno-tuner.

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Engine Modifications

Learn what engine modifications are appropriate for your car, and what you can do to your car to generate extra performance.

Superchargers : A supercharger is an air compressor used to force air into the combustion chambers of your engine at pressures higher than would otherwise be the case. It increases atmospheric pressure in the engine to produce more horsepower.

Turbos : A turbo is used to increase the amount of oxygen blown into the engine by compressing air that is entering the engine. This process will provide an increase in the engines power.

Intercoolers : An intercooler is a radiator used to lower the temperature of air compressed by the turbo. Thus increasing density of the air so more can enter the cylinders, thereby increasing engine power.

Camshafts : A camshaft consists of a cylindrical rod running the length of the cylinder bank with a number of lobes (cams) protruding from it, one per valve. The lobes push on the valve lifters to cause the valves to open and close.

Nos - Nitrous Oxide Sysytems : Nitrous oxide is an oxidizer, not a fuel. It carries more oxygen to the engine, allowing for faster burning of the fuel and generating more power. At high temperatures, such as those found inside a firing cylinder, nitrous oxide breaks down into nitrogen and oxygen gas. This raises the partial pressure of oxygen in the gas mix above the level found in normal atmospheric air, and lets the fuel burn more efficiently.

Nitrous oxide is also incorrectly called 'NOS' among racers after one of the first companies to provide nitrous systems, Nitrous Oxide Systems. This is normally sounded out by letter ("en-oh-es") by pro mod drivers, although some pronounce it as a word (like "naws"). Today, there are several competing companies in the field, including BOSS NOSS, NOS, ZEX, Compucar, Top Gun, Nitrous Pro Flow, Nitrous Express, Nitrous Works, Cold Fusion, and Edelbrock.

Nitrous systems can increase power by 45% or more, depending on configuration, and are usually built in one or two stages. All Pro Mod cars and some Pro Steet cars use three stages, for additional power.

Fans can easily identify nitrous-equipped cars at the track by the fact that most will "purge" the delivery system prior to reaching the starting line. A separate electrically-operated valve is used to release air and gaseous nitrous oxide trapped in the delivery system. This brings liquid nitrous oxide all the way up through the plumbing from the storage tank to the solenoid valve or valves that will release it into the engine's intake tract. When the purge system is activated, one or more plumes of nitrous oxide will be visible for a moment as the liquid flashes to vapor as it is released. The purpose of a nitrous purge is to ensure that the correct amount of nitrous oxide is delivered the moment the system is activated - Air or gaseous nitrous oxide in the line will cause the car to "bog" for an instant until liquid nitrous oxide reaches the intake.

Air Filters : Two main types of air filters are used in automobiles: the combustion air filter, and the cabin air filter. The combustion air filter prevents particulate matter from entering the engine's combustion chambers. This filter is commonly changed at oil-change time, but may be changed at longer or shorter intervals, depending on operating conditions of the vehicle.

Most modern, fuel-injected vehicles use a flat panel filter. This filter is usually placed inside a plastic box connected to the throttle body with a large hose. Occasionally these are replaced with a conical filter and cold air intake which, in most cases, includes a heat shield to protect the intake air from under hood temperatures, along with tubing to improve airflow into the throttle body. In many cases an improved air-intake system can produce an increase in power and efficiency.

Older vehicles that use carburetors or throttle body fuel injection typically use a cylindrical air filter, usually a few inches high and approximately a foot in diameter (the most common version is 14 inches in diameter and 3 inches tall). This is positioned above the carburetor or throttle body and secured with a metal lid. Replacing this lid with a chrome-plated version is a common and simple modification among car enthusiasts.

The cabin air filter is typically a pleated-paper filter that is placed in the "outside-air" intake for the vehicle's passenger compartment. Some of these filters are rectangular and similar in shape to the combustion air filter. Others, such as in the Ford Taurus, are roughly triangular in shape, so as to fit in the narrow curving space of the outside-air intake. Cabin air filter replacement has recently become an opportunity for increased billings and profits at professional oil-change locations. Improper removal and reinstallation of this filter can lead to water leaks (by misalignment of the water diverter or seals) and in rare instances, a cracked windshield. This filter is often overlooked and clogged or dirty cabin air filters can significantly reduce airflow from the cabin vents, as well as introduce allergens into the cabin air stream. Periodic, proper replacement will increase cooling and heating efficiency. A filter should be replaced annually to ensure optimal efficiency. Drivers can change their own filters or have the service done for them at an automotive service center.

Clutches : A clutch is a mechanism for transmitting rotation, which can be engaged and disengaged. In everyday use, the term clutch refers to a subcomponent of motor vehicle engine's transmission designed to allow engagement or disengagement of the engine to the gearbox or whatever apparatus is being driven. Invention of the clutch is attributed to Karl Benz.

There are many different vehicle clutch designs, but most are based on one or more friction discs, pressed tightly together or against a flywheel using springs. The friction material is very similar to the material used in brake shoes and pads and used to contain asbestos. Also, clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient, however these have a "grabby" action and are unsuitable for road cars. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate, depending on type, and the friction plate is released and allowed to rotate freely.

A wet clutch is immersed in a cooling lubricating fluid, which also keeps the surfaces clean and gives improved performance and longer life. A dry clutch, as the name implies, uses no fluid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch disks can compensate for slippage. Most Moto Guzzi and BMW motorcycles use a single plate clutch like a car.

In a car it is operated by the left-most pedal using hydraulics or a cable connection from the pedal to the clutch mechanism. No pressure on the pedal means that the clutch plates are engaged (driving), while depressing the pedal will disengage the clutch plates, allowing the driver to shift gears.

ECU An Engine Control Unit (ECU), also known as Engine Management System (EMS) is an electronic device, fundamentally a computer, that is part of an internal combustion engine, which reads several sensors in the engine and uses the information to control the ignition systems of the engine. This approach allows an engine's operation to be controlled in great detail, allowing greater fuel efficiency, better power and responsiveness, and much lower pollution levels than earlier generations of engines. Because the ECU is dealing with actual measured engine performance from millisecond to millisecond, it can compensate for many variables that traditional systems cannot, such as ambient temperature, humidity, altitude (air density), fuel octane rating, as well as the demands made on it by the driver. In addition, to a large degree it is able to compensate for the gradual wearing of the engine as it ages, which in practice allows it to extend engine life to two or three times that of engines of twenty years ago.

Fuel Pumps : A fuel pump is an essential component on a car or other internal combustion engined device. Fuel has to be pumped from the fuel tank to the engine and delivered under low pressure to the carburetor or under high pressure to the fuel injection system. Some fuel injected engines have two fuel pumps for this purpose: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine.

Forged Pistons In general, a piston is a sliding plug that fits closely inside the bore of a cylinder. Its purpose is either to change the volume enclosed by the cylinder, or to exert a force on a fluid inside the cylinder. Forge your pistons to make them stronger.

Fuel Injectors In trying to keep up with emissions and fuel efficiency laws, the fuel system used in modern cars has changed a lot over the years. The 1990 Subaru Justy was the last car sold in the United States to have a carburettor; the following model year, the Justy had fuel injection. But fuel injection has been around since the 1950s, and electronic fuel injection was used widely on European cars starting around 1980. Now, all cars sold in the United States have fuel injection systems.

Cam Gears Before adjustable Crane cam gears came around, it took hours to make a cam timing change. Adjustable cam gears are reliable, precise and affordable.

Forged Rods Urban legends abound in the gearhead community. One is: aluminum connecting rods don't work in street engines. Prior to the mid-'70s, that might have been true, however, introduction of the Bill Miller Engineering Forged Aluminum Connecting Rod in 1975 provided a glaring exception to that myth.

Pulley Kits Lighter pulleys increase horsepower by decreasing the parasitic effects that factory accessory pulleys have on a vehicles engine. The pulleys lightweight 6061 T-6 billet aluminum construction reduces rotating weight and increases efficiency. All pulleys have a tooth profile that is guaranteed to match Original Equipment (O.E.) specifications, elimination the chances of premature comprehensive instructions, performance belts and AEM decals. ¡VRemoval of torsional vibration damper NOT necessary.

Valve Springs Single and double updated valve spring sets are available for various applications.

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Agency Power Racing Downpipe Subaru WRX/STI 02+

Continually developing and enhancing the Subaru WRX and STI cars has been the goal of Agency Power. With a complete line up to make your Subaru the best in it's competition, Agency Power has just released their all new Racing Downpipe. This downpipe fits all Subaru WRX or STI cars from 2002 and up. The downpipe is full stainless steel with a cast bell mouth upper section. The thich flanges ensure a tight and strong seal. The downpipe deletes both your catalytic converters and bolts to all factory style turbos. The downpipes precision welds and polished piping give the AP Racing Downpipe that cutting edge. Each downpipe includes a bung for an aftermarket air/fuel sensor as well as a bung for the factory O2 sensor.

When adding an Agency Power Racing Downpipe to your Subaru WRX or STI, you will gain more horsepower and overall performance. The downpipe allows for better flow of the turbine and wastegate gasses. Unlike the factor downpipe that blocks the wastegate gasses from being released in an efficient manner, the AP downpipe has a large bell mouth which allows for both to flow smoothly out and down the pipe. The 3 inch diameter piping is the perfect size for the turbo cars from stock hp to 500 whp. The bellmouth will also allow for a little boost increase since there is less restriction. Mate this downpipe up with your aftermarket catback exhaust or one of our Agency Power catbacks for an amazing sound and almost 25 wheel horsepower gain.

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Nissan Skyline

The Nissan Skyline GT-R is an iconic Japanese sports coupé in the Nissan Skyline range. The Skyline name originated with the Prince automobile company which developed and sold the Skyline line of sedans before merging with Nissan-Datsun. The GT-R abbreviation stands for Gran Turismo Racer. The Japanese chose to use English as their first language when naming the car, as most cars made in Japan at that time used American abbreviation to further enhance sales. The earliest predecessor of the GT-R, the S54 2000 GT-B, came second in its first race in 1964 to the purpose-built Porsche 904 GTS race car. The next development of the GT-R, the 4-door PGC10 2000 GT-R , later to be superseded by the 2-door KPGC10 version, scored 33 victories in the one and a half years it raced and by the time it attempted its 50th consecutive win, its run was ended by a Mazda Savanna RX-3. The car took 1000 victories by the time it was discontinued in 1972. The last of the original GT-Rs, the KPGC110 2000GT-R, used an unchanged S20 160 hp (120 kW) inline-6 engine from the earlier 2000 GT-R and only sold 197 units due to the worldwide energy crisis. This model was the only GT-R to never participate in a race despite only having one built which now resides in Nissan's former factory turned storage unit for historical cars in Zuma.

The Skyline model became popular largely because it remained rear wheel drive, while most other manufacturers' models were front wheel drive (which had certain complexities inherent in achieving high performance in power or handling when compared to a rear-wheel drive car).

The Nissan Skyline R range houses the RB engine. Generally, R32s have RB20's and R33's and R34's have RB25s. Some later model R32s came with a non turbo RB25.

The Nissan Skyline GTR is one of the most loved performance cars to come out of japan. When the R32 GTR came out in 1989 it was considered to be way ahead of it time with the powerfull RB26DETT.

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Turbo Charger vs Super Charger

Turbocharger

Turbochargers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the charging. This can significantly improve the power-to-weight ratio for the engine. In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high. Turbochargers are powered by the mass-flow of exhaust gases driving a turbine.

Supercharger

Another way to add power is to make a normal-sized engine more efficient. You can accomplish this by forcing more air into the combustion chamber. More air means more fuel can be added, and more fuel means a bigger explosion and greater horsepower. Adding a supercharger is a great way to achieve forced air induction. In this article, we'll explain what superchargers are, how they work and how they compare to turbochargers. A supercharger is any device that pressurizes the air intake to above atmospheric pressure. Both superchargers and turbochargers do this. In fact, the term "turbocharger" is a shortened version of "turbo-supercharger," its official name. Superchargers are powered mechanically by belt- or chain-drive from the engine's crankshaft.

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