I'm kinda new to SLi and I can't find any solid info on whether to treat 660ti and 660 as seperate models or not for the purpose of SLi.

Basically the question is, Is it possible or even desirable?

Or will I have to beg a friend to upgrade and sell me his?

Not possible. They are misleadingly named and quite different cards.

You only SLI identical cards. The 660ti is much better than the 660.

So... Uhm.. I guess that means the 660ti Phantom is a different card aswell.

If so, then this SLi plan of mine might require some old part hunting. My friends 660ti is Phantom.

yeah both cards really need to be the same, they don't need to be identicle, so long as the actual chipset (the 660ti bit) is the same then you can miss-match other brands, what happens at that point is it'll only run as fast as the slowest card but its not reccomended and you may run into issues. If you're wanting to sli you're friends 660ti phantom than you'll need to find another 660ti phantom really.

Necroing this thread to add that running a 660ti in SLi with a 660ti Phantom does not seem to pose any particular problem.

Geforce Experience does not differentiate the two, the Phantom is merely listed as a standard 660ti(This might be due to underclocking caused by being SLi'ed with a slightly slower card).

Running spot free for a few months now.