http://wapedia.mobi/en/Turbocharger?t=8.
read 7.3. Comparison to supercharging
The turbine section of the turbocharger is actually a heat engine in itself. It converts the heat of the exhaust into power used to drive the compressor, thereby providing a more efficient compression of the intake air than can happen with supercharger, which uses up net engine power to drive its air compressor
read a book
you might learn something
hence are all cars tuned lean (>15afr) on spool up