• A vehicle's turbocharger pushes the air/fuel mixture into the combustion chamber, under pressure to create more horsepower. The turbocharger uses that rush of exhaust gases leaving the combustion chamber as a power source. It's a complicated and delicate operation and won't work if the turbocharger isn't installed correctly, or it it is not the right fit for the engine.
  
  

The Purpose of Turbocharging

• Engines without turbocharging depend on ambient air pressure to push air into the combustion chamber. Air around us presses down with a force of 14.7 pounds per square inch, or psi. Turbocharging adds as much as 50 psi to the ambient air pressure, giving each combustion chamber 2 to 4 times more fuel/air mixture to burn for each ignition cycle.
  
  

Air Flow

• The turbocharger sequence begins when exhaust gases leave the combustion chamber under pressure. The gases hit a fan within the turbocharger, spinning it up to 150,000 rpm. The fan is connected to yet another fan, which draws fuel and air from outside the engine and pushes it into the combustion chamber.
  
  The designers of the turbocharger had to create the fans out of the lightest material possible, so they would spin quickly, with efficient bearings to keep the fans in place, spinning with as little friction as possible.
  
  The outlets connected to the combustion chamber have to be large and smooth, and designed so that the fuel/air mixture can flow without restriction. The timing of the fans must be controlled. That ensures that the inlet and outlet valves are open when the pressure moves the pre-ignition fuel/air mixture into the combustion chamber and exits that chamber as planned. The size and design of the air filter and exhaust system affect the efficiency of the turbocharger.
  
  

Fuel Injection

• Fuel is introduced by injectors that spray it into the air flowing into the combustion chamber. The injectors can be located either upstream of the cylinders or next to each one. A computer chip controls the timing of the injection. Designers must know the location and size of the injectors to make an efficient turbocharger.
  
  

Cool Air

• The temperature of the air matters in turbocharging, because cold air is denser than hot air, and can carry more oxygen and fuel into the combustion chamber. Some turbochargers use a radiator, called an aftercooler, between the inlet fan and the combustion chamber. This must be large enough to cool the air sufficiently, and have inlet and outlet openings that are big enough to allow the fuel/air mixture to flow unhindered.
  
  

The Basic Numbers

• Turbochargers are measured by the size of the inlet and outlet pipes, called the inducer and exducer. This translates to the total amount of fuel/air mixture and exhaust gas that the turbocharger is capable of handling, measured in cubic feet per minute. The amount of fuel the injector is capable of delivering is measured in pounds per hour.
  
  The spin rate of the fans, and the capacity of the bearing supporting them, measures in revolutions per minute. And, the point at which the waste gate blocks exhaust gases from entering the turbocharger measures in pounds per square inch, as well as the horsepower increase from the turbocharger.
  
  

Lag

• Early turbochargers sat still while the engine was at low speed, and turned on when the engine reached between 1,500 and 4,000 rpm. Often the engine was sluggish before the turbocharger started, and some turbochargers produced an unmanageable increase in horsepower when they started working. This sudden change from under-powered to over-powered is called lag, and it can present engine problems. Lag has been tamed, however, through the use of twin turbos that are set to provide a boost at different rpm's.
  
  

Fit

• The turbocharger has to be the correct size, so it can use the force of the exhaust gases coming out of the combustion chamber efficiently. Smaller engines won't produce enough exhaust gas to spin the fans in a large turbocharger quickly. That prevents them reaching the correct speed in time to provide usable horsepower. A turbocharger that is too small for the engine won't be able to use all of the force of the exhaust gases, and may be damaged by the stress.