Just got a new GTX 660 Ti. Core clock at 915 with boost to 980 MHz and Memory of 1502 MHz. I know kepler architecture from nvidia has the gpu booster so I'm not sure on what is the safe core and memory limit for gtx 660 ti. Any help will be appreciated

Every chip is different. So can't say as to how far you'll be able to oc it. Btw if your satisfied with your current gpu performance , there is no reason for you to oc it
If you would like more performance then try oc-ing it using msi afterburner by gng up 20mhz on each time and putting the gpu on stress (furmark) . If your gpu crashes meaning you may have reached your limit. By then try cranking up the core clock/memory clock by 10mhz and soon to 5mhz to find its stable limit. If you would like higher , you could try increasing the voltages to get a better oc

Bear in mind too high voltages/oc may damage your gpu.

have a look on guru3d review:
http://www.guru3d.com/articles_pages/asus_..._review,27.html

U should increase ur voltage too ... how much i not sure lol =p

Increase memory clock (e.g. 100MHZ), if fails then lower the value and keep running the Furmark to test...

Then, increase the gpu clock (e.g. 10MHZ), if it passes the furmark test, keep increasing another 10MHZ, until it fails and u revert back to the previous highest clock..

Of course, u can play with voltage tweak too, but it's risky if excessive volts and u fry ur graphic card later.

nvr test it b4...660 seems enuf for games while on stock speed