So the night has passed and the glue has cured on the second Radeon HD 7970 and I got about to installing it. As I suspected, it was a very tight fit. I had to install the lower card first and then the other after it. If I ever need to take cards out it will have to be in the reverse order because upper card completely blocks access to PCIE slot lock. Video card with Arctic Cooling 7970 cooler installed is slighly more than 3 slots wide but it still fits. I’m quite happy with the reuslts.
Fans speed up just to about 35% when card goes from idle to full load and the difference in noise is impossible to measure.
Idle temperatures are at 53°C/49°C (for first and second videocard correspondingly) while noise level is 45dB.
At full load the cards warm up to 72°C/52°C and the noise level stays at 45dB. These are nice temperatures given the fact that cards with stock coolers ran hotter and were much noisier.
If I manually set fans to 100% power, the noise goes up to 48dB but temeratures drop to 43°C/39°C. I were into overclocking, I could do a lot with a videocard running this cool.
Final verdict: Arctic Cooling Accelero Xtreme 7970 VGA cooler rocks in CrossfireX configuration. You have to mind the size though…
I also did an experiment with upgrading Gigabyte Radeon HD 7970 with Noctua 80mm fans. Gigabyte card already had the radiators and heatpipes, but fans were noisy. I removed the cover with original 92mm fans and attached 3 Noctua 80mm fans to the videocard with rubber bands. Of course this was never meant to be a permanent solotion. The plan was if the experiment goes well, to have a custom made mounting bracket manufactured. I used 3 way ran splitter with PWM control to power the fans. Unfortunately the splitter had a large motherboard-style connector and no way to plugging it into mini-VGA connector. The only option was to force fans always to run at full speed.
I ran the test in a CrossFire config with other card being HSI 7970 with custom cooler already installed. I disabled the factory 1000Mhz overclock on Gigabyte so that both cards ran at even reference 925Mhz.
Idle tests went well with temeratures of 45°C/36°C and noise level of 45 decibels (with fans running at 100% speed).
Full load results were bad though. The card quickly heated up to 80°C, while it’s cousin with Accelero Xtreme stayed at 37°C. At that point I aborted the experiment since it seemed that tempteratures would be on par with stock cooler (though without noise at all). It seems that Gigabyte card just doesn’t have enough metal on it in terms of heatpipes (3 vs 8 on Arctic Cooling) and radiators (much less visibly) to remove heat no matter what fans you attach to it.
I put the oriignal cooler back and descided to stick with HSI 7970 + Accelero Xtreme and return the Gigabytes.
Of course there was also the water cooling option but I descided that given the reduced mobility of the desktop, risk of leaks and additional trouble when moving components inside the case that it is not worth it.
As I was typing this post I tried to overclock the cards to 1000Mhz, while keeping the fan at 100%. It seemed to be stable enough when crunching numbers in BOINC for MilkyWay@Home. While running at 63°C/57°C