Turbochargers 101

What Is A Turbocharger?

In its simplest form a turbocharger is an exhaust driven centrifugal compressor that feeds your engine with more air than it can normally ingest allowing a greater amount of power to be produced than the same engine normally aspirated.  Since all internal combustion engines rely on oxygen to burn their fuel, feeding more air, or oxygen, by the use of a turbocharger, more power can be produced.  In most cases, power increases of 50-75% will be achieved with turbo charging.  Normally, the exhaust gas by product of the combustion process is expelled from the engine out into the atmosphere. A turbocharger utilizes this normally wasted gas as an energy source to drive the turbine wheel before being returned to the exhaust system.  The turbine wheel has a shaft that connects it directly to the compressor wheel located on the opposite end of the turbocharger.  This compressor wheel draws in fresh air from the air filter assembly, then compresses it to provide a force fed charge of air for your engine utilize in combustion.  The turbocharger spins at an extremely high speed, some models approach 160,000 revolutions per minute to provide enough air flow to feed a hungry engine.  The turbo relies on oil suspended bearings to allow its shaft to rotate.  The speed at which the turbo turns, combined with the heat generated by the exhaust system equates to a very sophisticated part made with very specialized materials, machined and manufactured to strict tolerances.  A turbocharger rebuilding process is very labor intensive and requires specialized equipment and strong experience, we recommend always sending your turbocharger to a professional for repairs any needed.

What Is A Wastegate?

On most turbocharger systems you will find a very important part commonly referred to as a waste gate.  Since the turbocharger relies on the engines exhaust to drive the turbine, at some point there will be an excess of airflow energy available, so the need to control that flow to the turbo and subsequently, the boost pressure being produced, is the job of the waste gate.  The function of this part of the turbo system is fairly straight forward; it provides an alternate passage around the turbine wheel for the exhaust gas to flow.  Usually connected to the waste gate valve is the waste gate actuator.  This actuator will have a boost reference tied into the engine intake manifold and is designed to “actuate” or move once a desired amount of pressure signal is received.  This movement opens up the waste gate valve, allowing the turbine speed to slow, therefore equalizing the boost pressure available in the intake manifold of the engine.  On most production gasoline cars this pressure will be between 8-14 PSI at the intake manifold.  Almost all production cars will have some type of computer control over this pressure; usually this will be in the form of a waste gate control solenoid located in line with the vacuum signal going from the intake manifold to the waste gate actuator.  Allowing the computer to control the given boost is a safe guard against damage due to poor quality gasoline, differences in atmospheric conditions or even the load being placed on the engine due to gear position or operating conditions.

What Is A Compressor Bypass Valve?

Since a turbocharger’s drive energy is provided by the exhaust gases and its operational speed is dictated by engine load, a turbocharger has a very dynamic operating speed range.  When you are sitting still in traffic with your car at idle speed, the turbocharger is spinning at about 1/8th of it total capability.  Once you start to accelerate by opening the throttle its speed increases dramatically. In most cases it approaches 100,000 rpm or greater.  As you reach your comfortable speed and let off the throttle, the throttle plate partially closes to reduce the amount of air feeding the engine, but the turbochargers rotational speed carries a lot of inertia and once the throttle is closed the result is a pressure spike generated when the compressed air has nowhere to go.  The job of the compressor bypass valve is to relieve that pressure spike by bleeding off the unwanted air and redirecting back into the air filter assembly.  This keeps the turbocharger from enduring high amounts of load due to the rapidly changing rpm that is encountered while driving.

What Is An Intercooler?

The turbocharger is centrifugal compressor, and one of the by products of compressing air is the heat generated by that actual act of compression.  The design of the blades of today’s turbochargers compressor wheels make them very efficient, providing for the means of filling the engine with a large amount of air very quickly.  The high operational speeds of the compressor introduces a significant amount of heat into the air that needs to be reduced before it enters the engine, this is the job of the intercooler.  The intercooler in most cars uses ambient air passing over a radiator type core to cool the charged air.  Since the compressed air directly out of the turbocharger can approach 300˚F, and most outside air temperatures are 100˚F or less, the ambient air does a really good job cooling the intercooler and charged air before it reaches the engine.