Turbos

How does a turbo work?

A turbo works by compressing the air from the air intake before it enters the inlet manifold. The turbo is 'powered' by the exhaust gases.

The following diagram created by Matt Randolf simply explains this.  Click the image to enlarge.  Simply put, when you accelerate you allow more air and fuel to flow through the engine.  This in turn produces more exhaust output.  The turbo has two parts and is connected to the exhaust (exhaust turbine) and the air intake (compressor wheel).  The exhaust output travels through the up pipe to and through the turbo spinning a small turbine (a sort of fan in reverse, the airflow turns the blades not as in a fan where the blades create the air flow).  The exhaust gases travel on through the downpipe and out through the rest of the exhaust (See Exhausts).  The turbine that has been caused to spin by the exhaust gases is fixed on a shaft which has a compressor wheel (like a fan) which is forced to spin by the turning shaft.  This compressor wheel is connected to the air intake and the spin causes it to suck more air and push itthrough into the engine.  This increases the air pressure going into the engine which means it is more dense (compressed) and when this air passes out of the exhaust is expands causing more air flow and therefore faster exhaust gas to flow out of the exhaust port and into the exhaust side of the turbo thus spinning it faster and therefore turning the air intake compressor wheel faster which sucks more air etc.etc.     

Click to enlarge

So, why doesn't the power keep on climbing? It would, but this would eventually lead to the enging exploding so the ECU has control over a safety valve called a wastegate. When the MAP (manifold pressure sensor) signals to the ECU that the pressure in the inlet manifold has reached a pre-determined point the ECU will open the wastegate allowing the exhaust gas to be vented down the downpipe instead of flowing through the turbine of the turbo thus slowing the turbo down. Should the wastegate fail and stick closed then the ECU would cut off the fuel at a pre-determined manifold pressure (fuel cut caused by overboost).


Next: - Blow off valves