I have two 6950 in crossfire mode. I set the 6950 settings to the same as the 6970 ( 1.175 V, 1375 Mhz RAM, 880 Mhz core.) I have three issues. (1) Under heavy load I smell a hot electronics/plastic kind of smell. (2) The fan goes to 100% on one GPU (likely the one who's air flow is partially blocked by the other card) and the heat is around 85 C; (3) If I loop 3D Mark long enough, 3D Mark may crash.
I was surprised by this, because I thought the 6950 was pratically the same thing as the 6970 card. I would expect to be able to run 6970 cards in crossfire mode.
Could be any number of things causing these issues, so was looking for ideas, thanks.
(1) Very bad - you've got too much heat or are asking too much from the card's power circuitry.
(2) Also very bad - if the fan is at 100% it can't cool any better than that and may continue to build heat up to thermal throttling.
(3) If 3dMark is crashing and/or artifacting then it isn't a stable overclock.
When you are running at stock in XFire mode, how are your temps and fan speeds? It sounds like you already have a lot of heat build-up from the two cards and OCing them will only make that worse.
The burning smell is very bad - you are risking damage (and may already have it) if you continue to overclock those cards that high with that much heat. 85c for a Cayman isn't terrible, but a 100% running fan with a burning smell is very bad!
I wouldn't overclock those cards based on what you have said BUT - If you must overclock them, leave the ram clock at stock, start with the core clock then go up in increments and find where the sweet spot is on clock/voltage vs. heat. Try to use as little voltage as possible while maintaining stability. After finding the sweet spot you can increase the ram speed until you get either 1) instability or 2) loss of performance. Watch those temps and fan speeds! But really, I have to stress - since you've already noticed a burning smell and have heat issues, I wouldn't recommend overclocking your setup.
You are misinformed. They are not the same and almost is not the same. Even a modded 6950 card is not a 6970. I have modded many of them and know what I am saying about this. You will damage your cards if you continue to OC the way you describe. One of the issues of multi cards is air flow/heat. You seem to know what is going on but ignore the facts. Lastly I wonder what issues you have had in game playing? A pair of those cards at stock settings will play just about everything on the market at very high settings.
Trying to run at 6970 settings does not work well because it runs too hot. IMO, if the fans hit 100%, it's too hot IMO. After all, if it keeps getting hotter, there's no fan "headroom." Another poster also noted this factor.
I could spend a lot of time finding the point at which it would not run too hot and would be 100% stable, but it's not (currently) worth it. Thanks to larkspur for pointing out a good process for this (I decided on a similar sort of process not long ago.)
I went back to stock voltage for cooler temps, and ran the core clock to 645 Mhz, and it's stable so far. More performance would require a lot more work.
I did order a side case fan, which might help, if I get the energy to spend more time on this project.
I am slightly dissappointed I can't keep above 100fps at all times in Diablo 3 with my current setup, but that's more psychological than a real concern. Diablo's main lag comes early on in levels when it's apparently trying to load data, perhaps textures or models, and can't load them fast enough...an SSD would perhaps solve that, but mine is not large enough.
Dirt 3 runs amazing. Love how smooth the graphics are and how realistic they are ( don't much care for smashing and drifting, but I guess it's nice to have a break from rally.)