Mixed brand GTX660ti SLI issues

Hey guys, sad to say my first post has to be one made in distress, but after lurking and appreciating all the the 3rd-person experience and help, I figured I couldn't do much better for help.

So right after the GTX660ti's came out I did some research, and figured the best card for me to buy was a Zotac AMP! model, as it preformed well in benchmarks. More recently, I have been wanting more power so I bought a used PNY stock GTX660ti for a good price. Being familiar with SLI, I knew that the higher end card *SHOULD* underclock to meet the stock card for SLI, and then together could overclock at matching levels.

After installing the second card and enabling SLI, I noticed no FPS gain on BF3. MSI afterburner showed that with SLI enabled, the load was equally distributed as it should @ 40-60% each card, but no FPS gain was had in Identical environments with V-synch off. Then, with SLI-disabled, Load was put on a single card at 99% usage

Made sure to do the obligitory: Safemode>driversweeper>re-install. After that made no difference, I made a complete new install of windows- met with the same results.

Looking at GPU-z each card is retaining it's core clocks, The zotac@1006mhz boost and the PNY@980mhz boost. I have never seen this before with mixed brand cards.

I did several tests to Prove the following:

*That the used PNY card works 100% on it's own.
*That the core clocks were indeed different during usage
*That Both x16bit PCI lanes work and SLI is fully funtional
*SLI has no Effect on game Performance with mixed brands.

First I removed the functional Zotac card, and tested the PNY card on both PCI lanes. The card pushed through Furmark and Farcry2 bench just as the zotac had,with marginal differences.

I ran the PNY card on Furmark@ stock for 29 fps avg. then with a minor overclock for 31 fps avg.
Satisfied with this, I rebooted and enabled SLI and got a whopping 58 avg. FPS first run, and then 61avg. when applying the same minor OC.
Here is a pic of those results http://i.imgur.com/HZKigh.png

My celebrations were shortlived however when I ran Farcry2 bench again, and noticed no difference in the scene.
I ran 3 tests both with SLI-enabled and SLI-disabled, and saw the avg FPS lay between 85-95 in both cases.
Here is a Pic showing performance changes http://i.imgur.com/Dp9bDh.png
And here a pic showing the Differant core clocks during the test. http://i.imgur.com/HJofw.png

To push it home and show practical application, Here is a screen shot of afterburner showing Clear load distribution between both GPU's, and the heavier load when Only using the single GPU. In both instances I got 50-110 fps settling around 70 avg. http://i.imgur.com/6Aesyh.png


This is really bothering me and I'm at my wits end. Does anyone have any advice or theories?
4 answers Last reply
More about mixed brand gtx660ti issues
  1. Drivers?
  2. Like i said in the post, I made sure to go through the 3 available drivers for the 660ti, all in safe mode with the aid of driver sweeper.
  3. What about the BETA ones?
  4. Yea, unforutunatly with them being so new, there is only 3 nvidia available right now: WHQL 305.68, BETA 306.02, and WHQL 306.23.
    I notice no difference between the three. :S Thanks for looking though
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