How many watts for my psu

The bare minimum you can go with is 550 watts, at 100% your GTX 670 SLI and 3770k with 16gb of ram uses 494 watts, include a DVD Drive, and hard drive and you should just reach 550 watts. I would recommend you go a bit over just in case and settle with a 600 watt power supply. Remember to keep your power supply brands to be high quality like Antec, XFX, Seasonic, PC power and cooling, Corsair, Enermax etc.

Here is one example:
*note there will not be a power cord with this, I assume you have one if you have older computers or built others before.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

so 750 will work

http://www.evga.com/Products/Product.aspx?pn=120-PG-075...

ok thanks

Yes that will work as well, it is wise to buy that if you are upgrading soon again, but like I said above 600watts will be enough for your build if you do not plan changing any of the parts.

For a system using two GeForce GTX 670 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 700 Watt or greater power supply that has a combined +12 Volt continuous current rating of 45 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated @ 45-50°C ambient temperature, is the most important factor.

The EVGA SuperNOVA NEX750G Gold (120-PG-0750-GR), with its combined +12 Volt continuous current rating of 61 Amps and with four 6-pin and four (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two GeForce GTX 670 in 2-way SLI mode.