Imagine a shaft with turbine vanes at both ends; suspended in the middle by 'slipper bearings' (bushings which surround the shaft with pressurized oil when the engine starts up, so the shaft is spinning in a film of oil with turbine blades at both ends; there are seals that keep the oil from escaping).

A) One end is in the exhaust outlet. This end is the impeller: when the car is throttled up, exiting exhaust gases drive the impeller to speeds approaching 200,000rpm (This action is controlled by a 'wastegate' attached to an actuator rod. In it's purest form, this is a purely mechanical device. In today's turbocharged cars, the 850 included, the car's ECU controls wastegate operation).

B) The other end is in the engine air intake system. As the turbo spools up (driven by the exhaust impeller), it compresses air and rams it into the intake manifold for higher engine compression....and more power.

A normally aspirated engine under full throttle will have a vacuum of almost 30lbs in the intake manifold (that's MINUS 30lbs, takes your breath away.) Think of a runner with asthma. A Volvo with a high pressure turbo has sustained intake pressure of +11lbs. (That's PLUS, like being under 20 feet of water.) ECU reprogramming and other mods can carry the sustained pressure a few pounds higher.

This is a highly simplified description of turbocharger operations....there are a lot of attachments designed to manage performance, create fuel efficiency, cool (and intensify) the airpack, and provide turbo and engine longevity.

David
(98 S70 T5SE Black, misc mods (mostly lighting), red calipers) (92 940GLE)
(Previous: 86 240DL / 88 745T / 94 945T)