what is N/A and F/I?

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thanks to my350z for the info:

 

If you don't know how an engine works please first read this: http://en.wikipedia.org/wiki/Gas_engine

I hope those that don't understand F/I or N/A Engine find it helpful too.

Note: I did not write any of this. I found all of the below information at: http://en.wikipedia.org/wiki/Main_Page

 

-N/A is short for Naturally-Aspirated.

A naturally-aspirated engine (NA - aspiration meaning breathing) refers to an internal combustion engine (normally petrol or diesel powered) that is neither turbocharged nor supercharged. Most automobile gasoline(petrol) engines are naturally-aspirated, though turbochargers and superchargers have enjoyed periods of success, particularly in the late 1980s and the current 2000s era. However, most road-going diesel-engined vehicles use turbochargers, because naturally-aspirated diesels generally cannot offer suitable power:weight ratios to be acceptable in the modern car market.

 

Air or fuel-air mixture is forced into the cylinders by natural atmospheric pressure upon opening of the inlet valve or valves. The pressure within the cylinder is lowered by the action of the piston moving away from the valves (so as to expand the volume available for incoming air). In some cases the lowering of the cylinder pressure is enhanced by a combination of the speed of the exhaust gases leaving the cylinder and the closing of the exhaust valve at the appropriate time. A tuned exhaust can help with this but generally only works at a narrow range of engine speeds and hence is most useful in very high performance cars, aircraft and helicopters. Many NA engines today make use of Variable Length Intake Manifolds to harness Helmholtz Resonance, which has a mild forced induction effect but is not be considered true forced induction.

 

Natural aspiration gives less power than either turbo or supercharged engines of same engine displacement but is cheaper to produce and generally operates with better fuel efficiency. In drag racing, naturally-aspirated vehicles are vehicles that do not run a blower, a turbo, nor use nitrous oxide.

 

Many racing series specify NA engines to limit power and speed. NASCAR, Indycar, and Formula One are all in this category. Naturally-aspirated engines have been mandated in Formula One since 1989, in order to curb the excessive powers being developed by engines with superchargers or turbochargers.

 

-F/I is short for Forced induction.

Forced induction is a term used to describe internal combustion engines that are not naturally aspirated. Instead, a gas compressor is added to the air intake, thereby increasing the quantity of air or fuel-air mixture available for combustion.

 

Forced induction can be used to increase the power of an engine, its efficiency, or both, without much extra weight. Pressurizing the intake of combustion ingredients increases the effective capacity of the engine without an increase in physical size. The forced induction approach has the advantage that the intake pressure may be regulated according to the engine speed, thus providing power from extra capacity at high speed, but without wasting fuel at lower speeds.

 

The two different forced induction technologies in common use are superchargers and turbochargers. They differ mainly in the power source for the compressor.

 

-Supercharger (SC):

A supercharger (also known as a blower, a positive displacement pump or a centrifugal pumper) is a gas compressor used to pump air into the cylinders of an internal combustion engine. The additional mass of oxygen that is forced into the cylinders allows the engine to burn more fuel, which improves the volumetric efficiency of the engine and makes it more powerful. A supercharger is powered mechanically by belt- or chain-drive from the engine's crankshaft. It is similar in purpose to the closely related turbocharger, but a turbocharger is powered by the flow of the engine's exhaust gases driving a turbine. Superchargers may absorb as much as a third of the total crankshaft power of the engine, and in many applications are less efficient than turbochargers. In applications where a massive amount of power is more important than any other consideration, such as top-fuel dragsters and vehicles used in tractor pulling competitions, superchargers are extremely common.

 

In cars, the device is used to increase the "effective displacement" and volumetric efficiency of an engine, and is often referred to as a blower. By pushing the air into the cylinders, it is as if the engine had larger valves and cylinders, resulting in a "larger" engine that weighs less. Turbochargers are more commonly used in this role because they use otherwise "wasted" energy instead of using up power from the crank, but the supercharger reacts more quickly to power application and thus outaccelerates a car with the same amount of boost being provided by a turbo.

 

In 1900 Gottlieb Daimler (of Daimler-Benz / Daimler-Chrysler fame) became the first person to patent a forced-induction system for internal combustion engines. His first superchargers were based on a twin-rotor air-pump design first patented by American Francis Roots in 1860. This design is the basis for the modern Roots type supercharger.

 

It wasn't long after its invention before the supercharger was applied to custom racing cars, with the first supercharged production vehicles being built by Mercedes and Bentley in the 1920s. Since then superchargers (as well as turbochargers) have been widely applied to racing and production cars, although their complexity and cost has largely relegated the supercharger to the world of pricey performance cars.

 

Boosting has made something of a comeback in recent years due largely to the increased quality of the alloys and machining of modern engines. Boosting used to be an effective way to dramatically shorten an engine's life but, today, there is considerable overdesign possible with modern materials and boosting is no longer a serious reliability concern. For this reason boosting is commonly used in smaller cars, where the added weight of the supercharger is smaller than the weight of a larger engine delivering the same amount of power. This also results in better gas mileage, as mileage is often a function of the overall weight of the car and that is based, to some degree, on the weight of the engine, gas mileage can also be saved with a turbo because the engine does not have to have as much displacement therefore not needing to inject as much petrol in the the cylinders. Nevertheless, adding boost to a car will often void the drivetrain warranty. Also, improperly installed or excessive boost will greatly reduce life expectancy of the engine as well as the transmission (which may not have been designed to cope with additional torque).

 

There are three types commonly used in today's automotive world: Roots type supercharger, twin-screw type supercharger, and Centrifugal type supercharger.

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The Roots type supercharger or Roots blower is a positive displacement type device that operates by pulling air through a pair of meshing lobes not dissimilar to a set of stretched gears. Air is trapped in pockets between the lobes and carried between the intake side to the exhaust. The supercharger is typically driven directly from the engine's crankshaft via a belt. In order for most typical Roots superchargers to deliver air at greater pressure than atmospheric, they should be geared so that they turn faster than the engine. It is named for the brothers Philander and Francis Roots, who first patented the basic design in 1860 as an air pump for use in blast furnaces and other industrial applications. In 1900, Gottlieb Daimler included a Roots-style supercharger in a patented engine design, making the Roots-type supercharger the oldest of the various designs now available.

 

Out of the three basic supercharger types the Roots is considered the least efficient. However, it is simple and widely used and thus is invariably the most cost efficient. It is also more effective than alternative superchargers at developing compression at low engine rpms, making it a popular choice for passenger automobile applications. Peak boost can be achieved by about 2000 rpm. Much work has been done to improve the efficiency of the Roots type supercharger, but because it does not have internal compression (the design can be classified as just a "blower") it will never have the same potential as the twin-screw type supercharger, or the centrifugal type supercharger.

 

All supercharger types benefit from the use of an intercooler to remove heat produced during compression.

 

The Roots design is commonly used on two-stroke diesel engines, which require some form of forced induction since there is no intake stroke. In this application, the blower does not often provide significant compression and these engines are considered naturally aspirated; turbochargers are generally used when significant boost is needed.

 

The twin-screw type supercharger is a positive displacement type device that operates by pulling air through a pair of meshing lobes not dissimilar to a set of worm gears. Air is trapped in pockets between the lobes and carried between the intake side and the exhaust. The supercharger is typically driven directly from the engine's crankshaft via a belt. Unlike the Roots type supercharger, however, the twin-screw exhibits internal compression. As the air passes through the supercharger the air pocket decreases in size towards the outlet. This increases the thermal efficiency of the supercharger beyond that of the more common Roots style supercharger.

 

Although the twin-screw type supercharger has more potential than the Roots type supercharger, its production costs due to close tolerances put it at a cost disadvantage. Also due to the internal compression the air exiting the supercharger exhaust "pops", this can lead to a whine noise or whistle (or scream!) that has to be tolerated or dealt with via noise suppression techniques. Although not as ultimately efficient as the centrifugal type supercharger, it does not suffer from the latter's lack of low-rpm boost.

 

All supercharger types benefit from the use of an intercooler to reduce heat produced during compression.

 

Twin-screw superchargers are also known as Lysholm-type superchargers. Companies manufacturing automobile twin-screw superchargers include Lysholm, Eaton, Kenne Bell and Whipple.

 

The centrifugal type supercharger is practically identical in operation to a turbocharger, with the exception that instead of exhaust gases driving an impeller, there is only a compressor housing, and that is driven from the crankshaft via a drive belt. As such the centrifugal exhibits the same benefits and down-sides. Boost increases with the square of RPM (unlike the linear nature of the positive displacement devices), however low-rpm boost suffers due to the fact that air can pass back through the supercharger with little restriction until RPMs rise sufficiently to counteract the effect. Of all the belt-driven supercharger types this type exhibits the highest efficiency, and due to its design and lack of low-down boost is often employed on near standard compression engines. The Roots type supercharger and the twin-screw type supercharger, however, produce low-rpm boost and as such feel far more reactive on the road. Detractors of the centrifugal type supercharger note that it combines the worst qualities of a turbocharger and a supercharger, since it doesn't develop peak boost until redline (Turbo lag), but still uses up prodigious amounts of engine power to operate.

 

The Volkswagen G60 supercharger was invented by L.Creux circa 1905, the G in G60 standing for G-Lader (Lader being german for Charger), a supercharger whose interior resembles the letter "G". This supercharger is only mentioned here for completeness as it should not be confused with a centrifugal supercharger since it does not use centripedal force to compress air. The chambers within these superchargers reduce in size as the air heads towards the centrally located exhaust. Hence they are more like the twin-screw type supercharger in that are endowed with internal compression. They also make boost at low revolutions because of this.

 

The G60 engine was available in the VW Corrado but also in limited numbers in the VW Passat and the VW Golf. A similar, but smaller G40 equipped engine was available in the VW Polo during the early 1990s. The 40 and 60 denote the displacer scroll width in mm.

 

All supercharger types benefit from the use of an intercooler to reduce heat produced during compression.

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-Turbocharger: (Turbo), Also Single Turbo (ST) or Twin Turbos (TT):

A turbocharger is an exhaust gas driven compressor used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen entering the engine. A key advantage of turbochargers is that they offer a considerable increase in engine power with only a slight increase in weight.

 

A turbocharger is an exhaust gas driven supercharger. All superchargers have a gas compressor in the intake tract of the engine which compresses the intake air above atmospheric pressure, greatly increasing the volumetric efficiency beyond that of naturally-aspirated engines. A turbocharger also has a turbine that powers the compressor using wasted energy from the exhaust gases. The compressor and turbine spin on the same shaft, similar to a turbojet aircraft engine.

 

The term supercharger is very often used when referring to a mechanically driven turbocharger, which is most often driven from the engine's crankshaft by means of a belt (otherwise, and in many aircraft engines, by a geartrain), whereas a turbocharger is exhaust-driven, the name turbocharger being a contraction of the earlier "turbosupercharger". Because the turbine of a turbocharger is in-itself a heat engine, a turbocharger equipped engine will normally compress the intake air more efficiently than a mechanical supercharger. But because of "turbo lag" (see below), engines with mechanical superchargers are typically more responsive.

 

The compressor increases the pressure of the air entering the engine, so a greater mass of oxygen enters the combustion chamber in the same time interval (an increase in fuel is required to keep the mixture the same air to fuel ratio). This greatly improves the volumetric efficiency of the engine, and thereby creates more power. The additional fuel is provided by the proper tuning of the fuel injectors or carburetor.

 

The increase in pressure is called "boost" and is measured in pascals, bars or lbf/in². The energy from the extra fuel leads to more overall engine power. For example, at 100% efficiency a turbocharger providing 101 kPa (14.7 lbf/in²) of boost would effectively double the amount of air entering the engine because the total pressure is twice atmospheric pressure. However, there are some parasitic losses due to heat and exhaust backpressure from the turbine, so turbochargers are generally only about 80% efficient, at peak efficiency, because it takes some work for the engine to push those gases through the turbocharger turbine (which is acting as a restriction in the exhaust) and the now-compressed intake air has been heated, reducing its density.

 

For automobile use, typical boost pressure is in the general area of 80 kPa (11.6 lbf/in²), but it can be much more. Because it is a centrifugal pump, a typical turbocharger, depending on design, will only start to deliver boost from a certain rpm where the engine starts producing enough exhaust gas to spin the turbocharger fast enough to make pressure. This engine rpm is referred to as the boost threshold.

 

A disadvantage in gasoline engines is that the compression ratio should be lowered (so as not to exceed maximum compression pressure and to prevent engine knocking) which reduces engine efficiency when operating at low power. This disadvantage does not apply to specifically designed turbocharged diesel engines. However, for operation at altitude, the power recovery of a turbocharger makes a big difference to total power output of both engine types. This last factor makes turbocharging aircraft engines considerably advantageousâ€â€and was the original reason for development of the device.

 

A main disadvantage of high boost pressures for internal combustion engines is that compressing the inlet air increases its temperature. This increase in charge temperature is a limiting factor for petrol engines that can only tolerate a limited increase in charge temperature before detonation occurs. The higher temperature is a volumetric efficiency downgrade for both types of engine. The pumping-effect heating can be alleviated by aftercooling (sometimes called intercooling).

 

Design details

When a gas is compressed, its temperature rises. It is not uncommon for a turbocharger to be pushing out air that is 90 °C (200°F). Compressed air from a turbo may be (and most commonly is, on petrol engines) cooled before it is fed into the cylinders, using an intercooler or a charge air cooler (a heat-exchange device).

 

A turbo spins very fast; most peak between 80,000 and 150,000 rpm (using low inertia turbos, 190,000 rpm) depending on size, weight of the rotating parts, boost pressure developed and compressor design. Such high rotation speeds would cause problems for standard ball bearings leading to failure so most turbo-chargers use fluid bearings. These feature a flowing layer of oil that suspends and cools the moving parts. The oil is usually taken from the engine-oil circuit and usually needs to be cooled by an oil cooler before it circulates through the engine. Some turbochargers use incredibly precise ball bearings that offer less friction than a fluid bearing but these are also suspended in fluid-dampened cavities. Lower friction means the turbo shaft can be made of lighter materials, reducing so-called turbo lag or boost lag. Some car makers use water cooled turbochargers for added bearing life.

 

Turbochargers with foil bearings are in development which eliminates the need for bearing cooling or oil delivery systems.

 

To manage the upper-deck air pressure the turbocharger's exhaust gas flow is regulated with a wastegate that bypasses excess exhaust gas entering the turbocharger's turbine. This regulates the rotational speed of the turbine and the output of the compressor. The wastegate is opened and closed by the compressed air from turbo (the upper-deck pressure) and can be raised by using a solenoid to regulate the pressure fed to the wastegate membrane. This solenoid can be controlled by Automatic Performance Control, the engine's electronic control unit or an after market boost control computer. Another method of raising the boost pressure is through the use of check and bleed valves to keep the pressure at the membrane lower than the pressure within the system. If the wastegate was not in place to relieve boost pressure then when the throttle is released the engine would continue to rev up until it destroyed itself.

 

Some turbochargers utilise a set of vanes in the exhaust housing to maintain a constant gas velocity across the turbine, the same kind of control as used on power plant turbines. These turbochargers have minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. In many setups these turbos don't even need a wastegate. The vanes are controlled by a membrane identical to the one on a wastegate but the level of control required is a bit different. The first car manufacturer to use these turbos was the limited-production 1989 Shelby CSX-VNT. It utilised a turbo from Garrett, called the VNT-25 because it uses the same compressor and shaft as the more common Garrett T-25. This type of turbine is called a Variable Nozzle Turbine (VNT). Turbocharger manufacturer Aerocharger uses the term 'Variable Area Turbine Nozzle' (VATN) to describe this type of turbine nozzle.

 

Reliability

As long as the oil supply is clean and the exhaust gas does not become overheated (lean mixtures or retarded spark timing on a gasoline engine) a turbocharger can be very reliable but care of the unit is important. Replacing a turbo that lets go and sheds its blades will be expensive. The use of synthetic oils is recommended in turbo engines.

 

After high speed operation of the engine it is important to let the engine run at idle speed for one to three minutes before turning off the engine. Saab, in its owner manuals, recommends a period of just 30 seconds. This lets the turbo rotating assembly cool from the lower exhaust gas temperatures. Not doing this will also result in the critical oil supply to the turbocharger being severed when the engine stops while the turbine housing and exhaust manifold are still very hot, leading to cooking (burning) of the lubricating oil trapped in the unit when the heat soaks into the bearings and later, failure of the supply of oil when the engine is next started causing rapid bearing wear and failure. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure. A turbo timer is a device designed to keep an automotive engine running for a pre-specified period of time, in order to execute this cool-down period automatically.

 

Turbos with watercooled bearing cartridges have a protective barrier against cooking. The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat. It is still a good idea to not shut the engine off while the turbo and manifold are still glowing.

 

In custom applications utilising tubular headers rather than cast iron manifolds, the need for a cooldown period is reduced because the lighter headers store much less heat than heavy cast iron manifolds.

 

Diesel engines are usually much kinder to turbos because their exhaust gas temperature is much lower than that of gasoline engines and because most operators allow the engine to idle and do not switch it off immediately after heavy use.[/u]

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Lag

A lag is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo kick-in. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a supercharger does not suffer this problem. Conversely on light loads or at low rpm a turbocharger supplies less boost and the engine is more efficient than a supercharged engine.

 

Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spin-up to happen more quickly. Ceramic turbines are a big help in this direction. Unfortunately, their relative fragility limits the maximum boost they can supply. Another way to reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. Increasing the upper-deck air pressure and improving the wastegate response help but there are cost increases and reliability disadvantages that car manufacturers are not happy about. Lag is also reduced by using a precision bearing rather than a fluid bearing, this reduces friction rather than rotational inertia but contributes to faster acceleration of the turbo's rotating assembly.

 

Another common method of equalizing turbo lag, is to have the turbine wheel "clipped", or to reduce the surface area of the turbine wheel's rotating blades. By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust gases. This imparts less impedance onto the flow of exhaust gasses at low rpm, allowing the vehicle to retain more of its low-end torque, but also pushes the effective boost rpm to a slightly higher level. The amount a turbine wheel is and can be clipped is highly application-specific. Turbine clipping is measured and specified in degrees.

 

Other setups, most notably in V-type engines, utilize two identically-sized but smaller turbos, each fed by a separate set of exhaust streams from the engine. The two smaller turbos produce the same (or more) aggregate amount of boost as a larger single turbo, but since they are smaller they reach their optimal rpm, and thus optimal boost delivery, faster. Such an arrangement of turbos is typically referred to as a "twin turbo" setup.

 

Some car makers combat lag by using two small turbos (like Toyota, Subaru, Maserati, Mazda, and Audi). A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher rpm. Early designs would have one turbocharger active up to a certain rpm, after which both turbochargers are active. Below this rpm, both exhaust and air inlet of the secondary turbo are closed . Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher rpm range allows it to get to full rotational speed before it is required. Such combinations are referred to as "sequential turbos". Sequential turbochargers are usually much more complicated than single or twin-turbocharger systems because they require what amount to three sets of pipes-intake and wastegate pipes for the two turbochargers as well as valves to control the direction of the exhaust gases. An example of this is the current BMW E60 5-Series 535d.

 

Lag is not to be confused with the boost threshold, however many publications still make this basic mistake. The boost threshold of a turbo system describes the minimum turbo rpm at which the turbo is physically able to supply the requested boost level. Newer turbocharger and engine developments have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural. Putting your foot down at 1200 engine rpm and having no boost until 2000 engine rpm is an example of boost threshold and not lag.

 

Race cars often utilise anti-lag to completely eliminate lag at the cost of reduced turbocharger life.

 

On modern diesel engines, this problem is virtually eliminated by utilising a variable geometry turbocharger.

 

Boost

Boost refers to the increased manifold pressure that is generated by the intake side turbine. This is limited to keep the turbo inside its design operating range by controlling the wastegate which shunts the exhaust gasses away from the exhaust side turbine. Many diesel engines do not have any wastegate because the amount of exhaust energy is controlled directly by the amount of fuel injected into the engine, and slight variations in boost pressure do not make a difference for the engine.

 

Applications

Turbocharging is very common on diesel engines in conventional automobiles, in trucks, for marine and heavy machinery applications. In fact, for current automotive applications, non-turbocharged diesel engines are becoming increasingly rare. Diesels are particularly suitable for turbocharging for several reasons:

 

Naturally-aspirated diesels have lower power-to-weight ratios compared to gasoline engines; turbocharging will improve this P:W ratio.

Diesel engines require more robust construction because they already run at very high compression ratio and at high temperatures so they generally require little additional reinforcement to be able to cope with the addition of the turbocharger. Gasoline engines often require extensive modification for turbocharging.

Diesel engines have a narrower band of engine speeds at which they operate, thus making the operating characteristics of the turbocharger over that "rev range" less of a compromise than on a gasoline-powered engine.

Diesel engines blow nothing but air into the cylinders during cylinder charging, squirting fuel into the cylinder only after the intake valve has closed and compression has begun. Gasoline/petrol engines differ from this in that both fuel and air are introduced during the intake cycle and both are compressed during the compression cycle. The higher intake charge temperatures of forced-induction engines reduces the amount of compression that is possible with a gasoline/petrol engine, whereas diesel engines are far less sensitive to this.

 

Today, turbocharging is most commonly used on two types of engines: Gasoline engines in high-performance automobiles and diesel engines in work trucks. Small cars in particular benefit from this technology, as there is often little room to fit a larger-output (and physically larger) engine. Saab has been the leading car maker using turbochargers in production cars, starting with the 1978 Saab 99. The Porsche 944 utilized a turbo unit in the 944 Turbo (Porsche internal model number 951), to great advantage, bringing its 0-100 km/h (0-60 mph) times very close to its contemporary non-turbo "big brother", the Porsche 928. Contemporary examples of turbocharged performance cars include the Dodge SRT-4, Volkswagen GTI, Subaru Impreza WRX, Mazda RX-7, Mitsubishi Lancer Evolution, and the Porsche 911 Turbo.

 

Small car turbos are increasingly being used as the basis for small jet engines used for flying model aircraftâ€â€though the conversion is a highly specialised jobâ€â€one not without its dangers.

 

Most modern turbocharged aircraft use an adjustable wastegate. The wastegate is controlled manually, or by a pneumatic/hydraulic control system, or, as is becoming more and more common, by a flight computer. In the interests of engine longevity, the wastegate is usually kept open, or nearly so, at sea-level to keep from overboosting the engine. As the aircraft climbs, the wastegate is gradually closed, maintaining the manifold pressure at or above sea-level. In aftermarket applications, aircraft turbochargers sometimes do not overboost the engine, but rather compress ambient air to sea-level pressure. For this reason, such aircraft are sometimes refered to as being turbo-normalised. Most applications produced by the major manufacturers (Beech, Cessna, Piper and others) increase the maximum engine intake air pressure by as much as 35%. Special attention to engine cooling and component strength is required because of the increased combustion heat and power.

 

Turbo-Alternator is a form of turbocharger that generates electricity instead of boosting engine's air flow. On September 21, 2005, Foresight Vehicle announced the first known implementation of such unit for automobiles, under the name TIGERS (Turbo-generator Integrated Gas Energy Recovery System).

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-Intercooling:

An intercooler is a device used on turbocharged and supercharged internal combustion engines to improve the volumetric efficiency and increase the amount of charge in the engine, thereby increasing power. The inter in the name refers to its location compared to the compressors; the coolers were typically installed between multiple stages of supercharging in aircraft engines. Modern automobile designs are technically aftercoolers because they appear most often at the very end of the chain, but this name is no longer used.

 

Turbochargers and superchargers compress incoming air, causing it to become heated (see the universal gas equation). Since hot air is less dense than cooler air at the same pressure, the total charge delivered to the cylinders is higher than non-compressed air, but still less than it could be. By cooling the charge after compression, even more charge can be delivered, increasing power. Additionally, intercoolers help to increase the total amount of boost possible without causing engine knocking.

 

An intercooler is essentially a radiator tuned for high volume flow rates and the increasing density of the charge as it cools. Most designs use ambient air for cooling, flowing through the radiator core, and often collocated with other radiators for oil or cooling fluid. This approach is also known as Air To Air (ATA).

 

An alternate design, often referred to as a charge cooler, uses water or a water/antifreeze mix to cool the charge, then cools the water in a separate radiator. While heavier and more complex, charge coolers can often make arranging the rest of the engine much simpler. This approach is also known as Water To Air (WTA). A variation on this type of charge cooler substitutes a reservoir of coolant for the radiator, allowing the use of an icewater mixture that can bring outlet temperatures well below ambient air temperature even under very high boost pressure. Because of the limitations on the volume of icewater that can be stored and circulated, this approach to charge cooling is only practical for short durations, making it most common in drag racing and land speed record attempts.

 

Intercoolers need to be mounted so as to maximize air flow and promote efficient cooling. Most cars such as the Saab (except the Subaru WRX based 9-2X Aero), Mitsubishi Lancer Evolution, Volkswagen and Audi use front mounted intercooler(s) (FMIC) mounted vertically near the front bumper, in line with the car's radiator. In contrast, cars such as the Subaru Impreza WRX use top mounted intercoolers (TMIC) i.e. horizontally on top of the engine (due to its low hood line from the use of horizontally opposed engine) and use a hood scoop to force air over the intercooler. Some World Rally Championship cars use a reverse-induction setup, where air from ducts in the front bumper is forced up over a horizontally-mounted intercooler and then vented through ducts in the top of the hood to futher maximize aerodynamic benefits.

 

Supercharging versus Turbocharging

The physical space occupied by a turbocharger is significantly less than its direct-drive counterpart. This gives the opportunity of fitting multiple turbochargers to a single engine, such as in a "sequential turbo", where one turbo is tuned to give increased performance at low engine speed and another turbo is tuned to increase the high-speed engine performance.

 

An alternative arrangement utilizes two turbochargers of the same type, known as a "twin turbo". This gives a large power increase for a given engine speed at the cost of increasing the lag-time for the exhaust to heat up sufficiently to drive the turbochargers. This lag can be addressed by reducing the size of each individual unit such that the combined output is still as great as a single large turbocharger without having to suffer the lag-time required to reach operating speed.

 

A final benefit of the turbocharger over the supercharger is the operating speed; It is not unheard of for a turbocharger to reach 200,000 rpm. This is well beyond the operating specification of a supercharger.

 

The thermal efficiency, or fraction of the fuel/air energy that is converted to output power, is less with a mechanically driven supercharger than with a turbocharger, because the energy of the exhaust pressure is lost. For this reason, both the economy and the power of a turbocharged engine are usually better. The main advantage of an engine with a mechanically driven supercharger is better throttle response. This is important in dragsters and small sports cars. It also tends to run less hot.

 

It is also possible to drive the blower from the crank shaft and use an exhaust turbine for output power.

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