Can anyone explain, I have heard something about creating an air dam effect under certain conditions, what conditions?

once a turbo is spinning beyond its designed limit, it can reach a point where the impeller fins are moving too quickly to allow air to move in behind the displaced air from the fins. without resistance from the air, the turbo speed skyrockets... this is the reason for wastegates.

Thanks bob h.... :wink:

Also, if the turbo reaches a point past the line on the left of a compressor map (I forget what it's called, surge line?) basically the turbo will destroy itself. It does NOT have to be overspeeding for this to happen. Very rare on diesels, shouldn't happen if the turbo is selected properly.

what this mean; "a point past the line on the left of a compressor map"???

what happens when a turbo self-destructs in this manner?... I.E. - what actually fails when this happens?

http://www.turbocharged.com/catalog/compmaps/fig1.html

there is an example of a compressor map. All turbochargers/superchargers have them.

A turbo running to the left of the "surge line" will start surging violently, and could easily destroy. I don't know exactly what happens.

mostly happens in gasoline applications where the turbo isn't fitted correctly.