Power Supply Question?

[goldbmr]

I currently have a MSI-970A-G46 motherboard, a AMD FX-8350 processor, 8 gigs of ram, a 500gb hdd (7200rpm), a 120gb SSD, 3 fans, a dvdr drive, and a GTX 660ti. I currently have this running on a 520Watt PSU (which I'm not sure if I should be running it on that PSU wattage). I want to do a upgrade with SLI and get another GTX 660ti card, what wattage will be needed to do SLI on this PC? Thanks.

 

[ksham]

650W