7970 Crossfire Max Watercooled Overclock

I had another thread where I reached out to all on whether or not to CrossFire my 7970. Anyway I ended up doing that and I'm happy but also now interested in water-cooling these cards to get the very best from them.

Now before you think I haven't done my research, I have. I've done a lot of reading, worked out all the parts I need for my loop etc and am just about to press the button on ordering all the gear and getting going on the build.

But... what is troubling me, especially before I spend on all this, is what I can expect to get out of my cards on water. I can't find anything online that tells me what to expect as the max overclock with voltage on water blocks.

To summarize, both my cards do 1100mhz with 1.2 volts 100% stable in OCCT shader complexity = 8 on air. The plan is to go north of 1.25 volts on water where I can keep the temps in check. To make this all worth while I am hoping for at least 1200mhz, preferrably higher.

Can anyone please let me know what to expect in terms of overclocking 7970s on water? I may think again if significantly better results are not a certainty...

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  1. As a 7970 user who is waiting for his water blocks to arrive for it. I can say i have had the same thought's and honestly I have seen no write up or info on how far these can really be pushed on water
    I expect it will be just a case of trial and error
  2. kitsunestarwind said:
    As a 7970 user who is waiting for his water blocks to arrive for it. I can say i have had the same thought's and honestly I have seen no write up or info on how far these can really be pushed on water
    I expect it will be just a case of trial and error

    This lack of write ups of 7970s overclocking on water worries me. The blocks are sold out all over the place so people must have them... so why nothing evident on the web... unless the same people are disappointed and don't feel like posting the same.

    I am about to drop some serious money on water cooling gear, just want to know its going to make a difference beyond quieter running.
  3. In my honest opinion, it depends on the card itself. lol Temperature is load of ***. If you are lucky and purchase a card with good overclocking headroom, then thats exactly what you get. If you get a crap card, then thats what you get.

    Currently my card is at 75% fan speed, stock volts (1.174) and at 1090/1575. Temperature at full load (99% during bf3) is around 65 maximum (on a hot hot day).

    Now if i crank up voltage to 1.3 with fan speed at 100%, my max overclock is 1190/1575 (i didnt exceed memory under CCC values - wasnt that interested). At that clock + volt, my temperature is STILL around 65 MAX.

    So...... an extra 100 core clock after cranking voltage up to 1.3 with very very good temperatures should demonstrated that... yes u can get waterblocks.. but it probably wont mean *** in terms of clocking this particular card. Im pretty certain if i water block mine, i wont get any higher than 1190.

    Also had other people with the same situation as me (i use to follow this massive forum on overclocking the 7970 and towards the end of the thread alot of ppl ran into the massive wall (upping the voltage didnt allow extra overclockign headroom even with nice temperatures).

    But yea thats been my observations. Hopefully im wrong and someone can point it out and explain why so that you can feel better about your water block purchase.
  4. Hopefully I have some headroom. When I push too far, like 1150mhz with over 1.2v I have to run the fan at 80% to keep the card cool under 93-94 degrees. That is the verge of stability because it seems to error very quickly as soon as the temps go any higher. I am hoping if its water blocked I can put say 1.25v thru it, keep it under 60 degrees and find out just what it can do. But I will be disappointed if I do all that to find it only goes 25mhz higher for example before erroring even when cool.
  5. Hi, I recently sold a pair of Koolance watercooled 7970's (Sapphire versions with stock HSF-Ref design), cleaning house for Kepler testing and review.

    My main reason to go to water was to test the new Swiftech Edge HD kits. I did not see a huge increase in max overclocking on the core or memory, even with 1.3v on the core.

    On air I was able to get 1250mhz on one and 1230mhz on the other. Underwater and with 1.3v I was able to increase the overclocks to 1270mhz and 1235mhz. Memory remained constant I was able to run at 1700mhz on both cards with or without water.

    You will need a minimum of a 320mm rad to cool both 7970's and a single cpu. I was using a 240 rad and an extra 140 rad to keep load temps on the gpu's down to 52C max and cpu at around 59-62C (i5 2500K at 4.9ghz with 1.375v). I paired all rads with low noise 1200rpm Bitfenix Spectre pro fans. I am sure that with my 1850rpm Gentle Typhoons I could have reduced temps but at the cost of more noise.

    Go watercooling to reduce noise and temperatures. Do not go water expecting massive overclocks as you will be disappointed.

    Even the retail Powercolor LCS 7970 is clocked out of the box at 1100mhz core...

    I did not even bother running the 7970's at their max overclocks 24/7, only for benchmarking. For 24/7 I just increased powerslider in CCC to +20% and maxed out core and mem with no vcore increase at all. much more sensible even under water. A pair of these cards decimated any game including Crysis 2 and Metro at 2560 x 1440 ( the resolution I game at)...
    Good luck.
  6. Hi, thanks for the information, very useful.

    I game at 2560 x 1440 also, probably not evident to 1080p users but it does take a lot of GPU power to keep 60fps in all scenerios at that resolution and when you get used to 60fps constant you do become that bit more sensitive to any dips.

    It sounds like I am a bit more heat limited, as I can't get anywhere near your air cooling over clocks. Fully understand the points you are making however.

    I was planning 2 x 240mm rads so think I would be ok there. Can I just ask why you don't feel it sensible to bump the voltages even on water? My intention would be to run over volted to 1.25v 24/7 and had assumed the cooler temps would ensure longevity of the cards - I do want them to last as I really am not one to continually upgrade to the latest and greatest so this needs to see me through the next 2-3 years.

    I am reconsidering whether I really want to do this for circa 1200mhz, which given I only feel comfortable running my cards at 1025mhz currently to keep temps under 80 degrees would equate to another 175mhz or 17% on the cores. A lot of expense and hassle for 175mhz as additional overclocking was my primary objective here...

    Again thanks for the information, appreciated.
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