Turbo Charged : May the Force Be With You!

A Forced Induction System refer to any device that pressurizes the engines air intake to above atmospheric pressure.This will move air through the engine through the engine in an ideal manner making the engine less dependent on both cam timing and exhaust sizing for maximum power.A byproduct of pressurizing the intake system is that you can pack a denser charge of air and therefore fuel into a cylinder of a given size ,hence more power in the same way that you would by increasing the size of the cylinder.
A turbocharged engine therefore improves the power to weight ratio significantly gaining the advantage during competition.The turbo system set up comprises of a turbo unit,an exhaust manifold with provisions for mounting an external wastegate,exhaust downpipe,wastegate unit,a blow off valve,lines for oil supply and return,and options for both intercooler and a boost controller.The typical boost provided by a turbocharger is around 6 to 8 pounds per square inch (psi). You would expect to get a 30 to 40 % horsepower improvement depending on the type of engine used.

Operation-The turbocharger uses the efficient exhaust exhaust gas flow from the engine to spin a turbine,which in turn works a compressor that can spin up to 10,000 rpm, pressurizing the air into cylinders generating high boost.The exhaust gasses move from the cylinder into the exhaust manifold,then into the turbine housing's inlet. The moving gases find an airflow path through the turbine housing contacting the turbines blades causing them to spin as they rush out from the center outlet of the housing and into the exhaust down pipe. The more exhaust gas that goes through the blades,the faster the blades spin.The turbine is connected by a shaft to a compressor wheel which is located between the air filter and the intake manifold.
The compressor wheel is identical in function to a centrifugal supercharger albeit running backwards with a smaller compressor section.

Turbo unit: There are turbo designations eg T-25 G for each turbo unit and this refers to the overall size and basic flow potential.Manufacturers often provide a horsepower rating for each turbo unit.The turbine shaft is designed to handle speeds of up to 150,000 rpm (about 30 rimes faster than most car engines) and to withstand the soaring temperatures of the exhaust manifold.Therefore,it has to be supported by fluid/thrust bearing (a thin layer of oil that is constantly pumped around the the shaft supported by a bearing) to keep the shaft spinning efficiently.Bearings do wear and need to be changed after about 150,000 km of normal usage.There is both a supply and return oil cooling line for the serious turbo build up,where the supply line is generally in the form of a sandwich adapter mounted between the oil filter and engine block.The return line is usually connected to the oil pan:some aftermarket oil pans have NPT bungs on them ready for this type of use.Recently,water cooling is used in addition to oil,this serves two purposes ; it cools the shaft and some of the other turbocharger parts, and it allows the shaft to spin with less friction.The water cooling is said to provide reliability by helping to stabilize temperatures and prevent oil from cooking in the housing.A twin scroll ball bearing turbo charger is highly regarded as it is capable of channeling more air than stock with less lag due to its design. The ball bearing center is durable hence more reliable and efficient at transmitting power  to the compressor wheel at identical boost than the conventional sleeve bearing turbo.This means that the turbine spins on a roller bearing and not a bush for better performance. Turbo designers took advantage of the potentially higher shaft speeds caused by the ball bearings. they then design the rest of the components around the more efficient ball bearings to maximize performance.This allowed the turbochargers to have a higher redline because the shaft could be spun to higher rpm's.

Exhaust Manifold: This has a special flange opening to accommodate the turbine's housing inlet.Turbo chargers build up a tremendous amount of heat and pressure in the manifold: The thick cast iron manifolds are ideal for reliable performance in this hostile environment.Special tune headers with long runners may be more efficient in extracting exhaust gas but its material may not be resistant to extreme heat. Therefore,form had to follow function  which allowed for a compromise exhaust manifold. An exhaust gas temperature gauge  is recommended to help tuners combine both air/fuel ratio and EGT measurements for effective tuning.The EGT is also used as a warning indicator to suggest whether the AFR is relatively rich or lean. To get useful temperatures, the EGT probe,must be installed in the exhaust manifold before the turbocharger.

Wastegate: Exhaust gas if not regulated for use with a turbo system will spiral out of control. The wastegate job is to reroute exhaust gas away from the turbine wheel  preventing them from providing boost, thus regulating boost to preset levels.There are 2 types of wastegates , internal and external, both performing the same task but differ in location and effectiveness. Internal wastegates are located inside the turbine housing imparting some turbulence to the exhaust flow path.This increases exhaust pressure and hurts performance.
The external wastegate, is mounted before the turbo unit on the exhaust manifold.An entirely alternate flow path is created where exhaust gases skip going through the turbine housing altogether contributing less turbulence in the system. They also tend to be more accurate at controlling exhaust flow and turbo boost.

Blow Off Valve:
aka dump or bleed valve : too much boost can potentially harm the engine,hence a blow off valve is used to regulate the boost, while the waste gate manages over boost , the blow off valve will vent excess pressures to help maintain safe levels of boost.In operation,the valve remains closed until it detects that the preset boost
level  has been reached and then bleeds off excess pressure that builds up in the intake system.This can occur due to either boost creep or a sudden closing of the throttle body when boosting (such as during wide open throttle,high rpm's shifts) but either way its the blow off valves job to prevent pressure spikes in the intake side preventing detonation,it also prevents airflow from reversing direction back into the turbo charger The installation of the blow off valve can be identified by a distinct sound caused when backing off the throttle at gear change.Besides the ear candy , a blow off valve helps increase turbo life and minimize lag between shifts.For maximum efficiency, fit the blow off valve as close as possible to the throttle body.

Electronic Boost Controller:
A Quality Boost Controller allows easy programming at the touch of a button to increase boost pressure at a choice rpm. This will improve throttle response whilst maintaining consistent boost pressure.You will need an accurate boost gauge on the console to monitor this.If the boost pressure is too high,the compression ratio of the engine may have to be reduced to avoid knocking.It is also a good idea  for turbocharged engines to run on higher octane 98 RON or better fuel to minimize knock.Most modern turbocharged cars have enough margins in their ECU mapping and fuelling capabilities to withstand an additional 03 bar of extra boost.
If high boost is used on a fuel injected car , the software in the stock ECU may not be programmed to provide the required fuel and or the pump and injectors may not be capable of supply.Therefore , higher capacity fuel  injectors, an upgraded fuel pump, an adjustable fuel regulator and the ECU remapped will have to be considered to realize the full benefit of a turbo charger . It is pertinent to note that at high boost levels,the spark created by the spark plug can be be snuffed out, which is why spark plugs in the colder range should be installed. Besides providing more consistent spark,they wont over heat.

The instantaneous rise of boost typical in a turbo system forces your engine to run much closer to its limits of endurance. Therefore, the fuelling and ignition maps have to be set correctly, otherwise catastrophic engine failure is plausible.You wont find another bolt on product that adds as much raw power and torgue .Nevertheless, the whine of the turbine, the whistle of the blow off valve, and the dancing boost meter makes turbo charging irresistible.  Salam.