SLI and overclocking - Baffling...

Hi all.

First off, this is what I have:
2x Gainward 7900gs 265MB Golden Sample PCI-E cards in SLI
nVidia 93.71 driver.
3800+ X2 2Ghz @ 2.45Ghz.
570w SLI certified Hiper PSU
All watercooled.



This is the problem:
My cards overclock like hell individually, they won't overclock at all in SLI.

This is what i've done:
I installed one card, ran 3dMark05 at stock 450mhz core, 660mhz ram. I got 7137.
I overclocked the card to a colossal 653mhz core, 800mhz ram and got 8842

I installed the other card by itself in the other PCI-E slot and at stock got 7140, nearly exactly the same.
Again, I overclocked this card to the same 653mhz core, 800mhz ram and got 8846, nearly exactly the same.

I used Coolbits to overclock the cards.
Both with no artifacting, they run perfect.

So, I run both cards in SLI at stock speeds in 3dMark05 and I get around 9800, which isn't great, but it's still a sizeable increase over the stock 7137 of one card.

However, the cards simply won't budge at all when I try and overclock them in SLI. First I use coolbits, with no changes made to its value, nothing. I change the value of Coolbits to 1A for SLI, nothing. I use Rivatuner instead and I think I got an increase of 250 points, which is pathetic. If I go over 550Mhz, then I actually get a lower score. I installed Powerstrip, but that only lets me clock about 100mhz over stock, so i didn't bother trying; these cards do 200mhz over stock.


Both cards are PCI-E power-connected, with the bridge installed.

I am at an utter loss here, anyone have any idea? Thanks.




EDIT: Hmm, i've seen some people are having trouble with the 93.71 drivers in overclocking. I'll try switching down to a lower version.

Okay, i downgraded to 92.91 drivers and the cards are finally overclocking. But a dissappointing score results.

I get 12263 in 3dMark05 at 652mhz(450mhz stock) core and 800mhz(660mhz stock) ram, which is only a 915 increase, which is very low seeing as individually the cards see a 1700 point increase at that speed.

I really am baffled now...

You could try and downgrade the drivers again. I am currently running the 84.21 drivers and I never had any problems overclocking my 7800GS; reached 470/1500 from 375/1200 still haven't found my final oc. I know your card came out after mine, but it couldn't hurt to try them. Also, I haven't overclocked a SLi system..... yet

BTW, you in DkIT?

*Edit* Just saw your PSU. That PSU is way too week to overclock a SLi system. To run two 7900GS in SLi you need at least a 450W PSU. Your PSU could be a major factor in your low overclock in SLi mode.

my OC's were better when I ran SLI... I had older cards though

EDIT:

the_cultie said:

*Edit* Just saw your PSU. That PSU is way too week to overclock a SLi system. To run two 7900GS in SLi you need at least a 450W PSU. Your PSU could be a major factor in your low overclock in SLi mode.

Click to expand...

You're probably right. I had trouble running SLI on a 600W PSU.

its called a bottleneck, thats SLI for you, consider selling those $400 worth of 7900gs and pick up a 8800gts and you'll be much better off.

Rattle said:

its called a bottleneck, thats SLI for you, consider selling those $400 worth of 7900gs and pick up a 8800gts and you'll be much better off.

Click to expand...

You have to be having a laugh, an 8800gts over here is $725. And those cards only get around 16,000, I wouldn't even get that with my CPU either.
And if I could get these cards to overclock, i'd be in 15,000 territory, which is a 7900gtx SLI score. For a mere €340, which is a bargain over here.


And sorry to those of you who thought it might be a my PSU, but I just hadn't upgraded my signature yet.
I got a Hiper R 580w SLI certified PSU last week, and it can seriously push out the juice! I'll try downgrading my drivers again, see if anything changes, because I really think it is a driver issue.

And the_cultie, I am in DKIT indeed, been a member on this forum since I started some five and a half years ago! This is my last year I swear...

you wont get anywhere overclocking the 7900's without ocing your cpu, and I said GTS not GTX

I hit 8116 in 3dmark06 with a [email protected] and a 7950gx2 overclocked. Two 7900gt cards is sorta close to a 7950gx2, so perhaps that'll help.

I'm running a Athena 550w PSU, never had any problems with it BTW.

Here's the 3dmark06 compare link,
http://service.futuremark.com/compare?3dm06=595712

Rattle said:

you wont get anywhere overclocking the 7900's without ocing your cpu, and I said GTS not GTX

Click to expand...

I know you said GTS, so did I. That's how much they are.

Gonna try some older drivers tonight.

wow that one heck of a overclock! my cards cant take that high of a overclock the highest i got mine in sli was 610/900 but scored low. so iuse that find optimal clocks button and it set me at 558/768 i ran it at that and WOW!! big performance increase. i would say dont go for the highest o/c just look for your best settings. thats what i had to do or mabey these cards are just picky. i was able to get them up to 580/ 798 until my scores with start heading south

here are some bench marks :
using beta 92.91 drivers
3dmark06- 8458
3dmark05- 13958
3dmark03- 32341

try the 91.47 drivers. they seem to be the best of the most "recent" drivers.
i tried the 93.47(?) and 92.91 but i still have the best overclock and gaming experience with the 91.47s

i wish nvidia would have a way of updating/adding game profiles without having to switch to newer drivers. anyone agree?

Thanks for the posts guys.
It seems that none of nVidias drivers are allowing me to overclock in SLI.
I just installed the drivers that came with the cards, i've no idea what driver version they are, but they come with an interesting application called VDO Tool.

They have a performance section, which allows you to overclock to a maximum of 590mhz core and 800mhz ram. I cranked them up and I get a mere 400 more. Lowering the clock doesnt help.

Why on earth wont they overclock in SLI?! I've seen them both do 200mhz over stock!

voodoomelon said:

Thanks for the posts guys.
It seems that none of nVidias drivers are allowing me to overclock in SLI.
I just installed the drivers that came with the cards, i've no idea what driver version they are, but they come with an interesting application called VDO Tool.

They have a performance section, which allows you to overclock to a maximum of 590mhz core and 800mhz ram. I cranked them up and I get a mere 400 more. Lowering the clock doesnt help.

Why on earth wont they overclock in SLI?! I've seen them both do 200mhz over stock!

Click to expand...

This doesn't seem to be a driver issue.

But perhaps have you tried Rivatuner or Ntune?

Dear god, it gets worse.

I've tried nTune, Coolbits, Rivatuner and the VDO clocking tool with 91.47, 92.91, 93.71 drivers and the drivers that came with the cards, and the cards will overclock to a maximum of 500 points no matter what clock speeds i set.

The highest score i've got is with TweaksR US XTreme 92.91 drivers with a 915 point increase, using the inbuilt coolbits.

There's something really not right here and no-one seems to know what it is, i've really troubleshooted this into the ground and i'm all out of ideas.

One thing i've noticed is that when I run DriverCleaner and remove nVidia drivers after a clean, if i click clean immediately again it, nVidia files are still there. If I click clean again and again, it seems to just keep deleting the same files over and over.
And as there is a known issue with the 93.71 drivers and overclocking, which were the first drivers I installed, there could still be fragments of them left.

The only thing left for me to do is a full format, which is easily enough done.

Any other suggestions? I can't find anything else on the net....