SLI Testing

In our second round of tests, we will be looking at the cooling performance of our two cards when used in a dual-card SLI array. Because we only have one sample of each card, we unfortunately cannot bring you data on using two identical cards, so instead what we've done is test the two cards in alternate positions - with either the open-air or blower-style card on top. Due to natural convection, the top card in any SLI setup will always be under more cooling pressure, as it absorbs some of the heat from the card below. How much hot air it must contend with, of course, is directly related to the type of cooler being used by the lower card. As you'll recall from the previous pages, blower-style coolers generally function as more independent systems, but as will become evident shortly, they do not do well when fed a lot of hot air!

We'll start with idle testing to establish the noise levels of the fire-breathing 780 Ti SLI combo when not placed under a significant load. As shown in the graph below, the results vary only slightly depending on whether the open-air MSI or blower-style EVGA model is on top. No doubt about it though - the card on top is always going to be warmer. In the first set of data, you can see the MSI card at 22C and the EVGA card at 23C. Flip them and the MSI is now down to 21C, but the EVGA is up to 27C. Everything else is the same, including fan speeds, sound levels, and the CPU temperature. Particularly noteworthy is that at idle, this system with two video cards in it is no louder than it was with one card in it, as shown on the previous page.

SLI Idle

For our load tests, we actually needed to use a different benchmarking utility than the one we used in the single-card tests. As it turned out, Unigine Valley became far too CPU-limited to accurately assess the performance and cooling capabilities of our cards in SLI. We simply couldn't get the cards to stay above about 80% utilization. This was particularly concerning because when the system wasn't running at full load, one card ended up working harder than the other, leading to very skewed temperature results. So we turned to 3DMark, specifically the incredibly-demanding Fire Strike Extreme demo. We wanted our cards to be running as close to 99% utilization as possible, which is the maximum usage reported by onboard diagnostics. In the end, using Fire Strike Extreme, we were able to push our cards to about 97% utilization on average.

Another challenge in the SLI load testing was finding the exact fan setting that would hold each card at 80C at full load, given that the temperature and fan setting of the lower card would dramatically affect the temperature of the upper card. With an open-air cooler, the more hot air that's removed from the immediate GPU area, the more hot air there is in the case to choke other components. With the reference cooler, the more hot air removed from the GPU area, the more hot air ends up outside the case. Complicating matters is that you can't set independent fan curves for each card. As a result, we couldn't quite get both cards to run at exactly 80C, but we came close. In the end, after hours of testing, we arrived at the results below:

SLI Load

Not surprisingly, cooling performance varies dramatically depending on how the cards are configured in the case. With the MSI open-air model on top, the system is louder than in a single-card configuration, but not shockingly so, at just 39 dB. Furthermore, the EVGA blower-style model is holding it together, just 1C hotter than it was on its own, using a fan profile just 1% higher. Flip the cards to put the blower-style model on top, and the system goes haywire. The open-air MSI model is a ridiculously cool 71C despite running at its minimum 34% fan speed. In fact, it's far cooler than it was on its own, no doubt aided by the top-mounted EVGA card actually pulling hot air away from it. Of course, all that hot air is a serious detriment to the blower-style card, which required an 83% fan speed to keep its temperature at 81C. In the process, the blower pushes the system's noise level up to a very loud 43 dB, drowning out every other component in the system, including the CPU's relatively-loud liquid cooling system.

Again, we didn't have two open-air cards to try, but our hunch is that if we did, we'd find that the overall system noise would be higher than our setup with the open-air on top, blower on the bottom. A high-powered open-air card simply expels a huge amount of hot air into the case. No matter how good an open-air cooler is, when in the upper slot, it has to compensate for any extra hot air from the card below and will need to work a lot harder if the lower card is open-air as well. It probably wouldn't get as loud as our reference card did when on top, but it would be close.

One additional observation we'll make here is to point out the CPU temperature in the load results above. It's 51C in both cases. This is simply amazing, and a testament to the effectiveness of a self-enclosed liquid cooling system. While these systems aren't all that quiet compared to a good air cooler, particularly at idle, they are unfazed by what's going on around them. Even with the MSI GTX 780 Ti mounted in the upper-most PCIe video cared slot, dumping huge amounts of hot air into the CPU area, the CPU simply doesn't heat up. It's a far cry from what that same MSI card did to our poor reference-cooled EVGA GTX 780 Ti, which absolutely thrives on access to cool outside air.

Conclusion

So what have we learned? In short, always choose the product that suits your computing environment. Have a big case with plenty of cooling, especially a setup with liquid CPU cooling? You'll almost always be better off with an open-air cooler. Noise levels will definitely be lower overall. Have a small case or one with minimal airflow? Well, first of all, high-end open-air models might not fit as we discovered, due to their additional height and/or length. Furthermore, a blower-style cooler will be much more predictable, performing within its design parameters as long as it has access to outside air. Such models are particularly effective in ITX cases that position the video card's air intake at the edge of the case. Even if an open-air cooler could cool the GPU as effectively in such setups, the rest of the components in the case would suffer for it, due to the limited airflow inherent to any compact case.

Want to run two cards in SLI (or Crossfire)? Well, that's harder for us to draw conclusions on given that we didn't have two of each type of card to test with. We don't think you could surpass the performance of having a blower-style on the bottom and open-air on top, because the two cards basically operate as independent systems. On the other hand, we can't imagine a worse setup than an open-air cooler on the bottom and a blower-style card on top. It just doesn't work well to have the open-air card feeding hot-air to the blower-style card. Assuming you want to run matching cards, we would encourage you to go with two blower-style cards, for no other reason than that they won't take a serious toll on the other components in your system, and will both function about as well in tandem as they do on their own - no big surprises.

Alas, blower-style cards are becoming harder and harder to find. Currently, no high-end AMD Radeon cards are even available with blower-style coolers. This isn't surprising, given the terrible reception AMD's Radeon R9 290 and 290X cards received upon their Fall 2013 launch, as a result of their loud and ineffective blower-style coolers. Surprisingly, Nvidia's cards are increasingly unavailable with reference-style blowers as well, despite the acclaim Nvidia received for the cooler showcased in this review, first developed for the ultra-high-end GTX Titan in early 2013. Today, you'll find blower-style coolers on a few GTX 970 models (from PNYEVGA, and MSI), as well as on the range-topping EVGA GeForce GTX 980 Superclocked. Curiously, if you want an EVGA GTX 980 with the original Titan cooler we tested, you'll pay a price premium for it. This probably comes down to cost; a well-engineered cooler that made sense on a $1,000 Titan probably isn't as attractive to board partners when attached to a $500-$600 card, let alone a $300-$400 card. Don't expect to find it on many GTX 970 models - in fact, the only one it's on is an Nvidia-branded model, available only at Best Buy.

By the way, we thought we'd end with a little tutorial on how we used MSI Afterburner, a free download available here, to tailor our fan profiles. We figured some of our readers would appreciate learning how to do so, regardless of their video card or case setup. What you can see below is the fan profile we currently use for our MSI GeForce GTX 780 Ti Gaming. While you can set up a more linear fan curve, which gradually changes as temperature increases, we prefer a step-wise profile. Once we know the general operating temperature range of a card, we like to keep it at a constant fan speed, as the ramping up and down of a fan is much more noticeable than the consistent hum at a given speed. Our MSI card typically operates between 65C and 75C with a 44% fan profile, well below the default 83C threshold where voltage would be cut to reduce temperature. Note that this is a different profile than the one we used during our testing, which was intended to keep it pegged as close to 80C as possible for testing purposes. Now we have ours running at a 34% fan level all the way up to 65C (unfortunately, it won't go below that as indicated by the dotted line in the control panel), and then ramping up in steps until it gets to 100% fan at 83C. The great thing about manually setting up a profile is that you get to choose the balance of temperature and noise that suits your preferences. 

Fan Profile

Well, that's all we have for now. Hopefully you've learned a bit about the two most common video card cooling technologies available on the market today. As always, if you're looking to put together a new PC, check out our Build-Your-Own PC guides, which incorporate all the testing we do in our Gamer's Guides to give you, our readers, the best build advice possible.

Special Note: To read a more recent exploration of this topic, check out our article comparing the GTX 1080 Founders Edition against the open-air EVGA GTX 1080 ACX.

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