Arduino + motor driver shield output power?

what is output voltage (that voltage that goes to motors) in this set up (arduinos input voltage is 9v)

arduino http://www.ebay.com/itm/121844094217?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

arduino motor driver shield

The motor shield uses the L293D darlington H-bridge, so the motor(s) get about 2 to 2.5V less
than the motor supply voltage.

You need a powerful enough motor supply to operate motors, a small 9V battery is not
able to source enough current.

In general you should run the motor from a separate supply to the Arduino if you want
the Arduino to run reliably. That motor shield probably has a jumper to set whether the
motor supply is commoned with Vin on the Arduino or not.