Upgraded turbos flow more air more easily. You'll have cooler air with an upgraded turbo at, say, 15 psi then you will at 15 psi with a stock turbo. It also flows more air at that same 15 psi than a stocker. On my car I installed a TE-60 and it pulled harder at 10 psi than my stocker did at 15. Nothing else was changed. Of course with every goodie there's a baddie. Upgraded turbos spool up a little slower than stockers so a new convertor will be needed to match the spool-up of a stocker.