Scaling of Cooling Performance

The Scythe Infinity was an excellent performer in CPU cooling at stock speeds. However, as overclocks were raised, the performance of the single fan (stock) Infinity was below average. The Infinity reached relatively high overclocks, topping out at an average 3.83Ghz, but the cooling temperatures were higher than expected for a top cooler. It appears that this performance curve is mostly the result of the very low noise 1200 RPM fan Scythe ships with current Infinity coolers.

Further evidence that the low-noise fan is holding back cooling performance during overclocking can be seen by comparing the two fan Scythe Infinity results. Using two of the low-noise Scythe fans in a push-pull configuration significantly lowers the CPU temperature. In this configuration one fan pushes air through the cooling fins while the fan on the opposite side pulls the air. In other words both fans are blowing in the same direction toward the back of the case.

At 3.73GHz the retail HSF is running at 56C, compared to 43/41 with the Infinity in stock/dual fan setup. At every speed the idle performance is much improved with the push-pull fan setup. The delta becomes greater as the overclock increases. At 3.83GHz the idle with the stock single fan is 51C compared to the push-pull dual temp of 44C - a significant 7C improvement in cooling.

As described already, stress testing utilized the Far Cry River demo in a continuous loop for 30 minutes. Cooling efficiency of the Scythe Infinity under stress conditions was then compared to the retail HSF and other recently tested CPU coolers. Once again we tested both the stock and push-pull fan configurations.

By 3.83 GHz, which is the highest overclock the stock Infinity could reach with stability, the Tuniq is at 50C compared to the stock Infinity at 67C. Add a second fan to the Infinity with push-pull cooling, however, and the load temperature at 3.83GHz drops to 60C. What's more the dual fan Infinity can overclock higher - to 3.90GHz - to match our highest overclock on air with this CPU. That makes the push-pull Scythe Infinity the first air cooler to overclock to the same 3.90GHz reached with the Tuniq, which is excellent performance.

As stated many times, the overclocking abilities of the CPU will vary at the top, depending on the CPU. This particular CPU does higher FSB speeds than any X6800 we have tested, but the 3.9GHz top speed with the Tuniq is pretty average among the X6800 processors we have tested with Tuniq cooling. A few of the other processors tested with the best air coolers reach just over 4 GHz, but the range has been 3.8 to 4.0GHz. Stock cooling generally tops out 200 to 400 MHz lower, depending on the CPU, on the processors tested in our lab.

Cooling at Stock Speed Overclocking


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  • Zoomer - Thursday, March 1, 2007 - link

    Could you try adding more than two fans, or perhaps blocking the sides of the heatsink so that air can't escape and see if it helps?

    I'm very interested. It appears that this unit requires a high(er) static pressure to work well.
  • yyrkoon - Monday, February 26, 2007 - link

    These coolers, are all fine and dandy, but what about low profile coolers, that dont weight as much as the Golden Gate bridge ?

    Me, my personal case, is an Lian Li PC-G50 (silver, if you must know . . .), and the PSU sits right_above about half of the CPU. Silent is great, higher overclocking potential, is better still, but the bigger question is, why arent these companies working on anything that doesnt require special cases, or at the very least, cases that are so huge, you can not put them any place without having large amounts of room.

    My case: 15" tall, looks great, is very functional, its just a terrible shame, that no one seems to be making low profile coolers, that would help me eek out a 310mhz + CPU on my ABIT NF-M2 nView + AM2 Opteron 1210 (which I have actually achieved, just wouldnt do much other than BSoD within windows).
  • Lem - Wednesday, February 28, 2007 - link

    Have you checked the Thermalright "SI-type" coolers? I have been happy with a Thermalright SI-120 + 120mm 1200rpm fan (PAPST 4412F/2GLL). I am not much into overclocking though. I only raised the frequency of my X2 3800+ to 2.4GHz because it was a nice round number that my RAM could handle.

    The newer SI-128 seems to support AM2-socket as well. I prefer that design over these for obvious reasons.

    My Lian Li PC-61 is somewhat bigger than your case but I do not think that there would be any problems with PC-G50 either.
  • BigLan - Tuesday, February 27, 2007 - link

    "why arent these companies working on anything that doesnt require special cases"

    Erm, your case is the special one. These coolers generally fit in standard atx cases, with the regular atx-approved layout (height might be an issue in mid-atx cases.) I think that having the psu above the cpu is ok for micro-atx, but that is still pretty specialized - you might want to look into server coolers (specifically 1-u coolers.) m-atx-style normally requires smaller fans, which have to spin much faster to move the same amount of air, and are very, very noisy (does anyone remember the old 60mm delta screamers?) You're also limited to fin area, which also hurts performance. There are some reasonably good btx coolers which overcome these problems though, but they're often proprietary (built into dell cases etc.)
  • cujo - Tuesday, February 27, 2007 - link

    i love big cases. lots more room to work inside and lots more room for quiet 120mm fans. Reply
  • yyrkoon - Tuesday, February 27, 2007 - link

    Good for you. My case also has silent 120mm fans, the system is so quiet in fact, I have to turn something else on, so I can sleep ( I require white noise to sleep ). Reply
  • arswihart - Monday, February 26, 2007 - link

    I disagree with using overclocking as a measure of a heatsink's performance. You should focus on noise and temps, it's that simple. I don't know why anyone would even pay attention to that data you are presenting. Reply
  • Wesley Fink - Monday, February 26, 2007 - link

    Temperatures at stock speeds are reported on p. 4. However, contrary to your assumption, coolers that perform best at cooling at a stock 2.93GHz are not always the same coolers that enable the highest overclock. Temperature rises as a CPU is overclocked, and coolers that perform well at stock speeds do not always remove heat as well at higher temperatures.

    Since the OC that can be achieved does not matter to you, the data on p.4 - temperature at stock speed - should give you what you are looking for.

  • arswihart - Monday, February 26, 2007 - link

    Idle and Load temps for stock / OC. No need to look at 50Mhz differences to rank the heatsinks is my point. Reply
  • arswihart - Tuesday, February 27, 2007 - link

    To further make my point, you see a 7 C difference between the single and dual fan configs on the Infinity, and only a 70Mhz difference in OC. To me, the 70Mhz difference is negligible, while the 7 C difference is quite striking.

    Relatively speaking, the difference in temps is much more drastic (12%), and much mnore relevant, than the difference you are seeing in OC (2%).

    Do you still want to argue about it?

    Sure it makes for interesting reading, so I guess I can't blame you too much, and the audience at Anandtech surely eats it up. I would just tell you I'd rather not have reviews cluttered up with this rather petty data.

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