Turbo,
What I would like to know is if it is necessary to idle your engine to protect your turbo. How long must it idle, if necessary? Do you perhaps know how long it takes the turbo to slow down from maximum spinning speed? What kind of bearings are currently being used in turbos? We are having an debate about turbos here in South Africa and would appreciate any feedback on this regard.
Corrie-South Aftrica
That's great that we have readers as far away as South Africa. You'll have to e-mail us some photos of your cars there for Readers' Rides. In terms of your question, proper cool down time is extremely crucial when you drive the car hard or on the track. The purpose of allowing the vehicle to idle after a hard run is to allow proper cool down time of the turbocharger. Oil is fed into the turbocharger when the engine is on and besides lubricating the bearing assembly of the turbo it also cools the turbo by removing heat from the center cartridge. If an engine is shut down after a hard run the heat generated within the turbocharger can be hot enough to cook the oil (a.k.a. oil coaking), turning the oil into sludge that can eventually destroy the turbo by blocking the oil lines. The amount of cool-down time depends on how hard the vehicle was driven. Driving in bumper-to-bumper traffic would require about 30 seconds to a minute. A couple of hard laps at the track and the vehicle should be left running for about five minutes.
Regarding your question on how long it would take for a turbo to slow down from maximum speed depends on many variables (engine size, turbo size, ball-bearing, compressor and turbine blade weights, etc.) but we have seen a turbocharger spin for about a minute from a full boost run on a Supra.
Lastly, the two most common types of bearings found in turbochargers today are conventional bushings and full-ball bearing turbochargers.