your psu has 18A max on its 12V, which powers ur cpu/gpu etc.
total power on 12V = 18 x 12 = 216A
out of which your CPU will use 95W(if not overclocked).. which leaves 121A for the rest of the system,
the 6670 needs a minimum of 66W and max of 92W(if not overclocked). Which leaves upto 30A.. it is really cutting it close however the card will run fine.