A big turbo on a small engine needs a ported shroud since the turbo flows more air than the engine can use at first. The air then backs up in the intake and tries to turn the compressor wheel backwards, with the turbine spinning in the correct direction the two fight each other and ruin the bearings and scrape the housings. The ported shroud allows the air to recirculate to the intake of the compressor until the engine needs the extra air.
A ball bearing turbo does not ride on the oil wedge as a bushing does, therefore needs to be tighter . Also normally needs less oil flow or will pass oil to the turbine and exhaust. Always feel the play by pushing the wheels to the side of the housing for any rubbing action but don't try to make them hit, every time the turbo is off the engine.
Harry
Last edited by Turbo-6; 01/10/10 01:07 AM.
