TWIN-SCROLL TURBOCHARGER Twin-scroll turbocharger designs have two exhaust gas inlets divided by split walls inside the turbine housing, with both gas passages controlled by a waste-gate. A twin-scroll turbo recovers even more energy from the exhaust than a single-scroll turbocharger thanks to a divided manifold. The twin-scroll design separates the cylinders whose exhaust gas pulses interfere with each other resulting in improved pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger's turbine.

For example, at the start of the intake stroke of cylinder one, and when both the intake and exhaust valves of cylinder one are open (valve overlap period), cylinder three already starts its exhaust stroke with the exhaust valve open. If the exhaust passages of cylinder one and three were connected, the exhaust gas pulse from cylinder three would increase the back pressure of cylinder one. This would reduce the induction of the fresh air and increase the amount of hot residual gases inside the cylinder. However, with the twin-scroll turbocharger setup, this interference is minimized.

The result of this superior scavenging effect from a twin-scroll design leads to better pressure distribution in the exhaust ports and a more efficient delivery of exhaust gas energy to the turbocharger's turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side. At the same time, drawing out the last of the low-pressure exhaust gases help pack each cylinder with a denser and purer air charge. Maximum boost from the turbocharger is 17.4 psi.

The twin-scroll turbocharger design has several other advantages over traditional, single-scroll turbo charging systems, including:Improved combustion efficiencyLow engine-speed efficiencyKinetic exhaust gas energy is not wasted or trappedCooler cylinder temperaturesLower exhaust temperaturesLeaner air/fuel ratio

* Better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger's turbine

Differences between Variable Numeric Turbo and Variable Geometry TurboVariable Nozzle Turbochargers VAT

At low motor r.p.m.

At high motor r.p.m.The axial width of the inlet is selectively blocked by an axially sliding wall (either the vanes are selectively covered by a moving slotted shroud, or the vanes selectively move vs a stationary slotted shroud). Either way the area between the tips of the vanes changes, leading to a variable aspect ratio.

VGT Geometry

At low motor r.p.m.

At high motor r.p.m.A ring of aerodynamically-shaped vanes in the turbine housing at the turbine inlet. Generally for light duty engines (passenger cars, race cars, and light commercial vehicles) the vanes rotate in unison to vary the gas swirl angle and the cross sectional area.

Main compensations for fuel injection control

CompensationsContent

Oxygen sensor feedback compensationThe Oxygen sensor signal is used for making the compensation to get air-fuel ratio with best cleaning efficiency of the 3-way catalytic converter. This compensation might not be made sometimes in order to improve drivability, depending on driving conditions. (Air-fuel ratio compensation is made.) The engine-ECU compensates the output signal of the oxygen sensor (front) using the output signal of the oxygen sensor (rear). This allows the deviation of the output signal, caused by the deterioration of the oxygen sensor (front), to be solved, then the highly accurate exhaust gas control is performed.

Air-fuel ratio compensationUnder driving conditions where oxygen sensor feedback compensation is not performed, compensation is made based on pre-set map values that vary according to engine speed and intake air volume.

Engine coolant temperature compensationCompensation is made according to the engine coolant temperature. The lower the engine coolant temperature, the greater the fuel injection volume.

Acceleration/ Deceleration compensationCompensation is made according to change in intake air volume. During acceleration, fuel injection volume is increased. Also, during deceleration, fuel injection volume is decreased.

Fuel injection compensationCompensation is made according to the pressure difference between atmospheric pressure and manifold absolute pressure. The greater the difference in pressure, the shorter the injector drive time.

Battery voltage compensationCompensation is made depending on battery voltage. The lower the battery voltage, the greater the injector drive signal time.

Learning value for fuel compensationCompensation amount is learned to compensate feedback of oxygen sensor. This allows system to compensate in accordance with engine characteristics.

TURBOCHARGERSA turbocharger is an exhaust-driven supercharger (fan or blower) that forces air into the engine under pressure. Turbochargers are frequently used on small gasoline and diesel engines to increase power output. By harnessing engine exhaust energy, a turbocharger can also improve engine efficiency (fuel economy and emissions levels).The turbocharger consists of three basic partsa turbine wheel; an impeller or compressor; and housings that support the parts and direct the flow of exhaust gases and intake air. Basic operation of a turbocharger is as follows: When the engine is running, hot gases blow out the open exhaust valves and into the exhaust manifold. The exhaust manifold and connecting tubing route these gases into the turbine housing. As the gases pass through the turbine housing, they strike the fins or blades on the turbine wheel. When engine load is high enough, there is enough exhaust gas flow to spin the turbine wheel rapidly. Since the turbine wheel is connected to the impeller by the turbo shaft, the impeller rotates with the turbine. Impeller rotation pulls air into the compressor housing. Centrifugal force throws the spinning air outward. This causes air to flow out of the turbocharger and into the engine cylinder under pressure.A turbocharger is located on one side of the engine. An exhaust pipe connects the exhaust manifold to the turbine housing. The exhaust system header pipe connects to the outlet of the turbine housing.Theoretically, the turbocharger should be located as close to the engine manifold as possible. Then a maximum amount of exhaust heat will enter the turbine housing. When the hot gases move past the spinning turbine wheel, they are still expanding and help rotate the turbine.Turbocharger lubrication is required to protect the turbo shaft and bearings from damage. A turbocharger can operate at speeds up to 100,000 rpm. For this reason, the engine lubrication system forces oil into the turbo shaft bearings. Oil passages are provided in the turbo housing and bearings and an oil supply line runs from the engine to the turbocharger. With the engine running, oil enters the turbocharger under pressure. A drain passage and drain line allows oil to return to the engine oil pan after passing through the turbo bearings.Sealing rings (piston-type rings) are placed around the turbo shaft at each end of the turbo housing, preventing oil leakage into the compressor and turbine housings.Turbochargers require little maintenance between overhauls if the air cleaners are serviced regularly according to the manufacturers recommendations. The turbocharger turbine requires periodic cleaning to remove carbon deposits that cause an unbalanced condition at the high relative speeds at which the turbine must rotate.Turbocharging system problems usually show up as inadequate boost pressure (lack of engine power), leaking shaft seals (oil consumption), damaged turbine or impeller wheels (vibration and noise), or excess boost (detonation).There are several checks that can be made to determine turbocharging system conditions. These checks include the following: Check connection of all vacuum lines to the waste gate and oil lines to the turbocharger. Use regulated, low-pressure air to check for waste gate diaphragm leakage and operation. Use a dash gauge or a test gauge to measure boost pressure. If needed connect the pressure gauge to the intake manifold fitting. Compare to the manufacturers specifications. Use a stethoscope to listen for bad turbocharger bearings.Turbo LagTurbo lag refers to a short delay before the turbocharger develops sufficient boost (pressure above atmospheric pressure).As the accelerator pedal is pressed down for rapid acceleration, the engine may lack power for a few seconds. This is caused by the impeller and turbine wheels not spinning fast enough. It takes time for the exhaust gases to bring the turbocharger up to operating speed. To minimize turbo lag, the turbine and impeller wheels are made very light so they can accelerate up to rpm quickly.Turbocharger IntercoolerA turbocharger intercooler is an air-to-air heat exchanger that cools the air entering the engine. It is a radiator-like device mounted at the pressure outlet of the turbocharger.Outside air flows over and cools the fins and tubes of the intercooler. As the air flows through the intercooler, heat is removed. By cooling the air entering the engine, engine power is increased because the air is more dense (contains more oxygen by volume). Cooling also reduces the tendency for engine detonation.

Waste GateA waste gate limits the maximum amount of boost pressure developed by the turbocharger. It is a butterfly or poppet-type valve that allows exhaust to bypass the turbine wheel.Without a waste gate, the turbocharger could produce too much pressure in the combustion chambers. This could lead to detonation (spontaneous combustion) and engine damage.A diaphragm assembly operates the waste gate. Intake manifold pressure acts on the diaphragm to control waste gate valve action. The valve controls the opening and closing of a passage around the turbine wheel.Under partial load, the system routes all of the exhaust gases through the turbine housing. The waste gate is closed by the diaphragm spring. This assures that there is adequate boost to increase power.Under a full load, boost may become high enough to overcome spring pressure. Manifold pressure compresses the spring and opens the waste gate. This permits some of the exhaust gases to flow through the waste gate passage and into the exhaust system. Less exhaust is left to spin the turbine. Boost pressure is limited to a preset value.Manual Boost ControllerThe MBC, which is essentially a valve with an adjuster on it, has two hoses.One hose is installedat a location that provides an accurate boost source. The location that provides an accurate boost source could be any number of places a nipple on the compressor housing of the turbo, or another place in the intake system between the turbo and the intake manifold (basically, any location in the "charged" portion of the intake system). Different boost sources have different virtues, so turbo enthusiasts choose varying places to tap their boost source we recommend that enthusiasts of the novice level follow the manufacturer's recommendation as to where to tap an accurate boost source.The other hose is installedat theWastegate Actuator. In the picture below, the red arrow is pointing to the port on an actuator where the hose is attached. The Wastegate Actuator is the device that opens and closes the Wastegate, typically by means of an internal diaphragm, which cases an arm to move, which opens and closes the Wastegate.With ball-and-spring types, a spring-loaded ball is used to block this delivered boost "signal", until the desired boost level is attained. It is at this point, that the delivered boost pressure is strong enough to push the spring-loaded ball toward the spring and out of it's seat, allowing the signal to pass, and reach the Wastegate Actuator. The boost pressure then presses against the Wastegate Actuator's diaphragm, causing its arm to move, so that the Wastegate is opened. The opened Wastegate then allows the exhaust gases to divert away from the spinning turbine, thus preventing the turbo from boosting higher than the desired level.

The MBC is adjusted by turning a knob (or other adjustor), which varies the load on the spring inside the MBC. By adjusting it so there is more load on the spring, you are 'raising the boost" because more boost pressure is required to move the ball off its seat before the signal can pass to the Wastegate Actuator. By contrast, lessening the load on the spring allows the boost signal to more easily unseat the ball and continue on its voyage to the Wastegate Actuator, so by backing the adjustor away from the spring, you are "lowering the boost".

With bleeder types, a valve simply "bleeds" off some of the boost pressure that it receives. It always allows some boost pressure to reach the Wastegate Actuator, but the boost pressure that the Wastegate Actuator receives is always less than the level of boost pressure in the charged portion of the intake system (or the boost level delivered to the bleeder-type valve) because this kind of MBC basically is a controllable boost leak. Since the Wastegate Actuator does not receive the "full boost signal", it only opens the Wastegate when the amount of boost that gets past the "leak" is sufficient to force it open. The bleeder-type MBC is adjusted by changing the size of the leak. Closing the leak down lowers boost level, because more of the boost signal then reaches the Wastegate Actuator, opening the Wastegate sooner. Opening the leak wider raises the boost level, as more boost is released to the atmosphere, as opposed to being delivered to the Wastegate Actuator as a boost signal; so the opening of the Wastegate is delayed.

Electronic Boost ControllersElectronic boost controllers differ from manual boost controllers in that the valve they operate is controlled by an electronic solenoid and computer. Electronic boost controllers completely interrupt the flow of air into the wastegate. This means that the electronic boost controller can make the wastegate see 0 pressure (atmospheric pressure, really) and stay completely closed. This eliminates the issue of wastegates creeping open below the desired maximum boost level. When an electronic boost controller sees the maximum boost level desired it will then reconnect the flow of air to the wastegate and the wastegate valve will open to quickly limit the amount of exhaust flowing through the turbine. As soon as the amount of boost drops back to just below the max level the electronic boost controller will again disconnect the flow to the wastegate. Another advantage to electronic boost controllers is that they can variably limit the amount of boost developed according to other parameters. Since boost controllers are ran by computers that often have other data inputs you can control boost at different RPM levels, temperature levels, air-fuel ratios, gear, or whatever you have a sensor for really. The computer control of electronic boost controllers is far superior to manual boost controllers because it gives full control over when you limit the amount boost created and how much you limit boost levels by. You can limit boost to 5psi in 2nd gear but let it make 10psi in 3rd gear. There are also some applications that will lower the amount of boost allowed relative to temperature. If the engine is running too hot the boost controller will drop the amount of boost being created and allow the engine to cool down, avoiding damage to engine components. Certain boost controllers, like those offered by Gizzmo, also allow overboost or multi-scramble modes to temporarily run higher boost than normal. This means that if your engine safely runs 10 psi, but can handle 15 for short periods of the time, that the boost controller will limit boost to 10 psi until you hit a button and it will then push up to 15 psi for a few seconds. This can easily make the difference between winning and losing in a drag race.

Blow Off ValveA blow-off valve is vacuum/pressure actuated piston-type valve. It uses vacuum/pressure signals to tell the piston when to open and close.At idlethere is engine vacuum on the top of the BOV piston trying to suck it open, and no vacuum or pressure on the bottom of the piston. Since a vent-to-atmosphere BOV needs to be shut at idle to avoid air being drawn in through it, there is a spring inside a BOV with the job of holding the piston closed. The spring preload adjustment is to allow for differences in engine vacuum from car to car, and variations in atmospheric pressure at different elevations.On airflow metered cars the air drawn in through an open vent-to-atmosphere BOV at idle would confuse the ECU and cause over-fuelling and stalling and in any case, the air drawn in is unfiltered.Under cruiseconditions (off boost) the BOV is experiencing similar conditions to when the car is at idle, but there is less vacuum present on top of the piston because the throttle is partly open. If the BOV spring has been adjusted to keep the piston closed at idle, it will also be closed at cruise.On boostthere is boost pressure on both top and bottom of the BOV, the forces from which counteract each other, so the BOV remains closed.Immediately after the throttle is closed under boostthere is vacuum on the top of the piston and boost pressure on the bottom of the piston, which together, quickly open the BOV to release the pressure. When the pressure has been released, the BOV closes.

Latest Turbo TechnologiesTurbocharger for an exhaust temperature of 1050CThe turbocharger is also becoming more and more accepted in connection with the gasoline engine. The advanced charging technique will cause the percentage of turbocharged vehicles to steadily increase. The exhaust temperatures of future turbocharged gasoline engines will increase. The air ratio ? at the rated output point is currently about ?=0.750.85 since a portion of the fuel is used to cool the inside of the engine. If the air ratio is increased to a value between ?=0.9-1.0, then a potential fuel savings of up to 20% can be attained. However, this leads to an increase in the exhaust temperature of up to 1050C and places new demands on the turbocharger, among other things.Turbochargers for exhaust temperatures of 1050 C require a material for the turbine housing that will withstand such high component temperatures during the entire service life of the vehicle. Heat-resistant cast steel is ideal for this purpose. Turbine housings made of heat-resistant cast steel are already being used today by BorgWarner Turbo Systems for mass-produced customer engines.In addition to the turbine housings, the increased exhaust temperatures also result in extreme conditions for the turbine wheels. In this case, as well, BorgWarner Turbo Systems can provide a solution thanks to continuous refinement of the materials and connecting technologies previously in use. The bearing housing was redesigned with a highly efficient water cooling system in mind. The V-band clamp was introduced to ensure a secure connection between the bearing housing and the turbine housing at high temperatures.The thermal inertia of the turbine housing is of great significance to very low emission vehicles. Due to the low level of thermal inertia, the temperature in the catalytic converter during the cold-start phase of the engine rises quickly. The conversion of the pollutants in the exhaust starts early in this case. The thermal inertia and the surface area of the turbine housing are to be kept as small as possible to keep emissions low.The thin-walled turbine housingThe complexity of the manufacturing and machining processes for turbine housings made of cast steel and the high costs arising in connection with them has raised the question of what benefits the customer derives from these technologies. Thin walls are desired to significantly reduce the weight of the turbine housing and simultaneously reduce the thermal inertia of the turbine housing. This leads to faster activation of the catalytic converter during the cold-start phase of the engine, which in turn significantly improves the emission levels of the vehicle.

The sheet-metal turbine housingAnother promising solution can be found in the form of an sheet-metal turbine housing. It consists of several stamped sheet-metal parts that are welded together. The turbine housing can have a single-flow or double-flow construction with air-gap insulation.The turbine housing in the exhaust system of the engine can be connected to its exhaust manifoldes by a flange or the pipes can be welded on. As a result of this, it is possible to have continuous air-gap insulation for the flow of exhaust from the cylinder head all the way down to the catalytic converter. Heat resistant sheet metal is available as a material that permits exhaust temperatures of up to 1050C. Aluminum turbine housings are just as good as cast turbine housings in terms of their efficiency and throughput, yet they have much less thermal inertia and therefore allow the catalytic converter to be activated faster during a cold start.The newest generation of charging systems from BorgWarner Turbo Systems fulfills the higher demands of future gasoline engine generations in regards to turbocharging and provides the customer with solutions for all gasoline engine applications.Regulated 2-stage turbocharging (R2S)Schematic of the R2SThe basic development goals for future combustion engines for automobile and commercial vehicle applications make more refined charging systems necessary. The design of such a charging system leads to conflicting goals in terms of the rated output of the engine on one hand and the transient response and the range of maximum torque on the other hand. You need a relatively large exhaust turbocharger to attain the nominal output point. The desire for a very high boost pressure even at low engine speeds means, however, that the turbine and the compressor need to be made much smaller. A combination of the two would be ideal.To resolve this conflict, BorgWarner Turbo Systems has developed regulated 2-stage turbocharging. It meets the demands of an optimal design and allows for the continuously variable adaptation of the turbine and compressor sides of the system for each engine operating point.With this newly developed charging system, BorgWarner Turbo Systems offers the engine manufacturer an additional extremely high-performing charging system for future engine generations that fulfills the highest requirements in terms of power, fuel consumption and emissions.The regulated 2-stage turbocharger consists of two turbochargers of different sizes connected in series that utilize bypass regulation. The exhaust mass flow coming from the cylinder flows into the exhaust manifold first. Here it is possible to expand the entire exhaust mass flow using the high pressure turbine (HP) or to redirect some of the mass flow through a bypass to the low pressure turbine (LP). The entire exhaust mass flow is then utilized again by the low pressure turbine (LP).The entire fresh air flow is first compressed by the low pressure stage. In the high pressure stage, it is compressed further and then the charging air is cooled. Due to the precompression process, the relatively small HP compressor can reach a high pressure level so that it can force the required amount of air to flow through the system.At low engine speeds, i.e. when the exhaust mass flow rate is low, the bypass remains completely closed and the entire exhaust mass flow is expanded by the HP turbine. This results in a very quick and high boost pressure rise. As the engine speed increases, the job of expansion is continuously shifted to the LP turbine by increasing the cross-sectional area of the bypass accordingly.Regulated two-stage turbocharging therefore allows for continuous adaptation on the turbine and compressor sides to the actual requirements of the operating engine.The system can be regulated via pneumatic actuators that control the bypass valve in the same manner as when used in mass-produced turbochargers with swing valves. This makes it possible to model a compact charging system (when detailed knowledge of the complex system response is available) that fulfills the highest torque, response and power requirements while utilizing proven components.Titanium compressor impellersModern commercial vehicle turbochargers are subject to very high loads due to the wide range of applications they are used in. In many cases where there are extreme loads, a compressor impeller made of an aluminum alloy determines the service life of the turbocharger. In particular, material fatigue can result from extreme loads, especially when the loads are cyclical loads occurring at low frequencies. This phenomena is also known as low cycle fatigue (LCF).Various measures can be taken to increase the service life. For example, the circumferential speed of the compressor impeller can be reduced by changing the aerodynamic design of the impeller or by controlling or reducing the charging pressure. High-strength aluminum, for example, that manufactured using the HIP technique, is often used to reduce variations in the strength of the material. The high-end solution using aluminum consists of milled compressor wheels which were also developed by BorgWarner Turbo Systems.The increasing number of engine applications with high cyclical loads as well as the necessity to have higher charging pressures to remain within the stricter emission regulations have made an additional innovation step beyond the moulded aluminum compressor wheels necessary. In order to provide a customer with a technology that can withstand these loads and also ensure a service life that is just as long as it would be under standard conditions, BorgWarner Turbo Systems initiated a special development program.The demands on the compressor impeller stated above make it necessary to use higher quality materials since the potential for improvement inherent in aluminum is just not sufficient anymore. The engineers at BorgWarner Turbo Systems decided to use a titanium alloy that is not only very hard, but also provides an excellent strength-to-thickness ratio.With the titanium compressor impeller, BorgWarner Turbo Systems is now able to offer different compressor impeller technologies for special application requirements and special cyclical loads. In this manner the customer can select between cast or moulded aluminum compressor impellers or between cast or moulded titanium compressor wheels depending on the area of application.eBoosterFuel consumption and pollutant emissions always play a large role in the development of new engine generations. Next to further fuel consumption optimizations for diesel engines, the development of efficient and clean gasoline engines is increasingly becoming the focus of vehicle manufacturers.Promising starting points for reducing fuel consumption are, for example, the reduction of the displacement and a reduction in the number of cylinders in the combustion engine, which is also known as downsizing. The loss of power and driving comfort resulting in the use of smaller displacement engines as compared to the power and driving comfort of its higher capacity brothers, in particular the lack of torque in the lower RPM ranges, need to be compensated for through the use of a suitable, powerful charging system. In addition to turbochargers with variable turbines or regulates 2-stage turbocharging systems (R2S), electrically assisted charging systems are increasing being viewed as a possible solution.As the leader in technology in the field of charging systems, BorgWarner Turbo Systems has emphatically pushed for the development of the innovative eBooster concept. This electrically assisted charging system uses a flow compressor driven by an electric motor placed as a component before or after the turbocharger. In contrast to electrically assisted turbochargers, this system works with two stages, i.e. like two turbo-machines connected in series. In doing so, the pressures of the two charging units are multiplied.Schematic of eBoosterThrough the use of two perfectly matched flow compressors it is possible to optimally adapt the entire system to the particular purpose and expand its entire power curve. eBoosters and exhaust turbochargers are also separate units. This has the distinct advantage that, when suitably positioned, the thermomechanical stress on the electrical and electronic components is significantly less than with electrically assisted turbochargers.The eBooster permits the development of small and efficient high-performance turbocharged engines whose dynamic response matches that of large non-supercharged engines of the same output class. The superiority of the eBooster was impressively demonstrated in close cooperation with various customers for gasoline engines as well as for diesel engines.

Method Employed to reduce Turbo LagAnti-lag system(ALS) or misfiring system is a system used onturbochargedenginesto minimizeturbo lagon racing cars. It works by arranging for fuel and air to be in the exhaust duct after the engine, and before the turbocharger. This ignites in the hot ducting and the combustion process that occurs there keeps the turbocharger spinning when the engine is not delivering enough exhaust gas.Retarding ignitionThe throttle bypass/throttle solenoid system is combined withignitionretardation and slight fuel enrichment (mainly to provide cooling), typically ignition occurs at 35-45 ATDC. This late ignition causes very little expansion of the gas in the cylinder; hence the pressure and temperature will still be very high when the exhaust valve opens. At the same time, the amount of torque delivered to thecrankshaftwill be very small (just enough to keep the engine running). The higher exhaust pressure and temperature combined with the increased mass flow is enough to keep the turbocharger spinning at high speed thus reducing lag. When the throttle is opened up again the ignition and fuel injection goes back to normal operation. Since many engine components are exposed to very high temperatures during ALS operation and also high pressure pulses, this kind of system is very hard on the engine and turbocharger. For the latter not only the high temperatures are a problem but also the uncontrolled turbo speeds which can quickly destroy the turbocharger. In most applications the ALS is automatically shut down when the coolant reaches a temperature of 110-115C to prevent overheating.Inlet bypassAn ALS system working with a bypass valve which feeds air directly to the exhaust system can be made more refined than the system described above. Some of the earliest systems of this type were used byFerrariin F1. Another well-known application of this type of anti-lag system was in the WRC version of the 1995Mitsubishi Lancer Evolution IIIandToyota Celica GT-Four(ST205). Brass tubes fed air from the turbocharger's Compressor Bypass Valve (CBV) to each of the exhaust manifold tracts, in order to provide the necessary air for the combustion of the fuel. The system was controlled by two pressure valves, operated by the ECU. Besides the racing version, the hardware of the anti-lag system was also installed in the 2500 "Group A homologation base WRC method car" street legal Celica GT-Fours. However, in these cars the system was disabled and inactive. The tubes and valves were only present forhomologationreasons. On theMitsubishi Evolutionlater series (evo 4-9, JDM models only) the SAS (Secondary Air System) can be activated to provide Antilag.Turbo and intercooler bypass (D-valve)A method by which a large zero cracking pressure one-way check valve is inserted just prior to the throttle body, enabling air to bypass the turbo, intercooler, and piping during periods where there is negative air pressure at the throttle body inlet. This results in more air combusting, which means more air driving the turbine side of the turbo. As soon as positive pressure is reached in the intercooler hosing, the valve closes.Sometimes referred to as the Dan Culkin valve.When used in a MAF configuration, the D-valve should draw air through the MAF to maintain proper A/F ratios. This is not necessary in a speed-density configuration.Two-step Anti-lag/launch controlA method of anti-lag developed along the same technique previously mentioned, but designed only to allow reduction of turbo lag when a car is initially pulling away from a standing start. These systems can be integrated into the engine management or existing anti-lag system, or can be fitted as a standalone unit. The basic method of operation is to artificially lower the engine rev limiter to hold the engine at a speed where the turbo can produce usable boost, by altering the ignition. Because the ignition is alternately cut or retarded, there is similar noise and misfires associated with other anti-lag systems. Systems for two-step launch designed to be fitted in addition to the existing engine management work by interrupting the crank position sensor signal, so that the engine develops a controlled misfire at a pre-determined RPM. The basic premise of the launch control system is to build positive boost pressure from a static engine, releasing full or increased power to the wheels when the car starts to move off. It is most commonly used in turbo-charged drag racing, primarily in the US, Australia, Puerto Rico and Japan, although most WRC cars utilise launch control to ensure that the cars can get off the line much more quickly.Ball Bearings and TurbochargingSome turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. But these are not your regular ball bearings -- they are super-precise bearings made of advanced materials to handle the speeds and temperatures of the turbocharger. They allow the turbine shaft to spin with less friction than the fluid bearings used in most turbochargers. They also allow a slightly smaller, lighter shaft to be used. This helps the turbocharger accelerate more quickly, further reducing turbo lag.Ceramic Turbine BladesCeramic turbine blades are lighter than the steel blades used in most turbochargers. Again, this allows the turbine to spin up to speed faster, which reduces turbo lag.Sequential TurbochargersSome engines use two turbochargers of different sizes. The smaller one spins up to speed very quickly, reducing lag, while the bigger one takes over at higher engine speeds to provide more boost.Another optional feature is the intercooler. We'll take a look at one on the next page.Intercoolers and Turbocharging

An intercooler or charge air cooler is an additional component that looks something like a radiator, except air passes through the inside as well as the outside of the intercooler. The intake air passes through sealed passageways inside the cooler, while cooler air from outside is blown across fins by the engine cooling fan.

The intercooler further increases the power of the engine by cooling the pressurized air coming out of the compressor before it goes into the engine. This means that if the turbocharger is operating at a boost of 7 psi, the intercooled system will put in 7 psi of cooler air, which is denser and contains more air molecules than warmer air.Twin Scroll TurbochargerTwin Scroll Turbo sometimes called a twin scroll turbocharger or twin scroll turbine is an improvement to the normal or single scrollturbocharger. The twin scroll turbocharger is connected to the exhaust manifold via two input lines leading to the turbine and two scrolls where separate wastegates controls the gases from each input. The two input lines is used to separate cylinders whose exhaust gases would interfere with each other because of their firing sequence in thefour stroke cycletherefore allowing a more effective flow of exhaust gases to the turbo. The pulse of exhaust gases from the cylinders interfere with each other because the exhaust valves of one cylinder will be open when it finishes the exhaust stroke and begins the intake stroke and at the same time the exhaust valves of another cylinder will be opening as it begins the exhaust stroke. This overlap could cause some of the exhaust gases from one cylinder to mix with the fresh intake of air/fuel of another cylinder thereby reducing the amount of gasses going to the turbo and it would reduce the power from the combustion of the fresh air/fuel mixture in the new cylinder. Attention must now be paid to the firing order of the cylinders so no cylinder would be paired with one that directly behind it in the firing sequence. The design of the intake to the turbo ensures that the pairs don't mix. When the gases reach into the turbo it rotates its own small scroll to spin the turbine. Although the entire turbo operates as one unit the separate scrolls act as small turbos separately but together form a large turbo equivalent to single scroll turbo of the same size.Nomenclature for a MHI TurboMitsubishi Heavy Industries' (MHI) turbocharger nomenclature, such as TD04-13G-6cm2, requires some explanation. "TD04" and "TD05" refer to the turbocharger housing (either turbine housing or compressor housing or both), including the center housing (or CHRA or cartridge section). There are different styles of the basic housings and these have different suffixes appended to the basic designation, such as TD04L, TD04H, TD04HL, TD05, TD05H, and TD05HR.

TD04 housings have part numbers that start with 49177. TD04L housing part numbers start with 49377. Part numbers for TD04H and TD04HL housings start with 49189. The TD04HL compressor housing is easily distinguished from the others because of the integrated by-pass valve (see the pictures of the SL/MK TD04-18T hybrid below). The TD04LR-16Gk-6cm2 turbo (used on the turbocharged 2.4-L I-4 engine in the new PT Cruiser GT and SRT-4 Neon) is unique and not usable on our cars: the turbine housing is cast into the exhaust manifold, the impeller spins counter-clockwise, and the bypass valve is cast into the compressor housing.

All TD05, TD05H, and TD05HR housings start with 49178. The TD05HR turbine housing (found on the Mitsubishi Lancer Evolution IV through VIII) is a twin scroll design. All the other TD04 and TD05 turbine housings have a single volute in the turbine housing. Like the TD04LR, the "R" in the designation refers to the fact that the turbine wheel spins in the reverse direction (counter-clockwise) compared to the standard TD05H turbine.

The MHI part numbering system, and the possible combinations, can be somewhat overwhelming and confusing. For example, the MHI Sport Turbo Upgrade for our cars is usually referred to as the TD04L-13G-6cm2. This turbo clearly has the standard TD04 (49177) housings (at least by external appearances). However, both the stock TD04-09B-6 and the upgrade TD04L-13G-6 use the 49377 cartridge (but note the different complete part numbers) from the TD04L turbos. TD04 turbos used in other cars (even some other TD04-09B turbos) use the 49177 cartridge.

The "13G" in the model name refers to the compressor wheel. The "13" is the size and the "G" is the style. The 13G wheel has an exducer (or base) diameter or 2.000" and an inducer diameter (air intake opening) of 1.580". All MHI wheels I have seen have 12 blades. Blades are always evenly spaced, but the pitch and height of the blades can change between models. "B"- and "C"-style compressor wheels have all blade tips at the same height. "G"-, "Gk"-, and "T"-style wheels have blade tips at two heights, alternating high and low.

Mitsubishi does not seem to use seperate designations for different size turbine wheels, other than the TD04, TD04H, TE04, TD05H, etc., designation. The "6cm2" in the model name is similar to the A/R ratio used by other manufacturers. The "A" in an A/R ratio is the cross-sectional area of the smallest intake passage in the turbine housing before the passage spreads around the circumferential volute that leads to the turbine wheel. The "R" in the ratio is the distance from the center of the "A" to the center of the turbine wheel.The MHI "6cm2" designation is just the "A" in the A/R ratio, that is, it is just the cross-sectional area. Like A/R, the smaller the size of the "cm2" number, the faster the exhaust gases will discharge onto the turbine wheel, and so the faster the spool up will be (less "lag"). The size of the "cm2" number or the A/R ratio also determines the amount of exhaust gas backpressure and, thus, reversion into the combustion chamber. A larger "cm2" number (or larger A/R) means less backpressure at high exhaust flow.Extreme Turbo says that the TD05H-7cm2 housing is equivalent to a 0.50 A/R. The Rocky Mountain DSM turbo guide presents the following conversion between Mitsubishi's "cm2" number and the standard A/R.

6 cm2 = 0.41 A/R 7 cm2 = 0.49 A/R 8 cm2 = 0.57 A/R 9 cm2 = 0.65 A/R 10 cm2 = 0.73 A/R 11 cm2 = 0.81 A/R 12 cm2 = 0.89 A/R

Types of Boost ControllerBleed type Boost ControllerLike all boost controllers, a bleed type controller is installed on the Wastegate vacuum line. It can be installed anywhere on that line, but usually it is best to install the controller as close to the Wastegate as possible and to try and keep that vacuum line as short as possible. The way this controller works is by bleeding off pressure out of the line. The amount of air bled off is what controls the boost. Understanding a bleed type controller is best understood with example. Lets say we have a 10 PSI Wastegate set-up. Under normal conditions the vehicle runs 10 PSI. If we install a bleed type boost controller on the vacuum line heading to the Wastegate that bleeds off 2 PSI of air, then the Turbocharger will now makes 12 PSI. This is because the Wastegate will not open till 10 PSI is reached, and the boost controller is bleeding off 2 psi, so it will take 12 PSI of pressure from theturboto make 10 PSI to open the Wastegate.* Pros1. Very solid boost control. No wandering of boost pressure.2. Controller least susceptible toboost spiking.*Cons1. While itMAYnot hinder boost response, it doesnt help spool response like the other controllers can.Ball and Spring Type Boost Controller

- Aball and spring type boost controlleris exactly what is says it is. It is a ball with a spring behind the ball. The ball blocks the flow of air until the air pressure over comes the spring. It is installed in-line on the vacuum line leading to the Wastegate. Most manual Ball and Spring type controllers are adjusted by tightening down the spring making it harder to open and therefore requiring a higher pressure out of the turbo to open the wastegate.* Pros1. Can easily and quickly adjust boost pressures.2. Can keep the Wastegate fully closed longer during spool up, which allows the turbo to spool faster and be more responsive.*Cons1. Is susceptible toover-spikingbased on the design of the boost controller.Electronic Solenoid type controller

- Each company has many different ways that they control the solenoid so we will just generalize how the solenoid works without getting into particulars. An electronic solenoid is installed on the Wastegate vacuum line and functions like a Ball and Spring type controller by hiding the boost pressure from the Wastegate until a certain boost level is reached. The solenoid, being electronically controlled, is held shut until it is fed voltage by its controller and opens. The effectiveness of the solenoid is based on how well it is controlled by itscomputerand the software behind it.*Pros1. Can be controlled from inside the vehicle.2. Can be adjusted on the fly.3. Can increase the boost response and spool of the turbo.4. Can very the controller infinitely to help suppress boost spiking.*Cons1. Set-up and programming can be daunting for beginers.As you can see there is more than just one way to control the amount of boost a turbocharger will put out by manipulating the wastegate. Choose whichever one works best for your set-up and your wallet. Remember.....the most important thing is setting the controller up properly.

Diploma in Motorsport Technology(DMS) 2504Turbocharger Performance Tuning

Student: Lai Jih YanStudent I.D: DMS201107-00296NRIC: 911229-07-5519Instructor: Mr. Minrad