SLI Testing

SLI Bench

We're going to turn back to our big ATX system for the last round of testing, but this time, we're actually going to be challenging this well-cooled setup. That's because we're going to run two cards in SLI, which changes the thermal dynamics entirely. To add to the fun, we're going to bring in our third GTX 1080 sample, so we can test three different SLI setups. First you'll see our matched ACX cards, which is what most enthusiasts probably think will be the obvious choice for an SLI setup. Teamed up using our EVGA High-Bandwidth SLI Bridge that offers a serious boost to Pascal-based GPUs, they certainly look pretty impressive. If this were a beauty contest, the show would be over!

Alas, we're hear to find the best-performing setup, not the best-looking setup, and that means we're going to throw our Founders Edition card back into the mix. Below you can see the other two arrangements we tested. On the left, we have an ACX card on top, with a Founders Edition on the bottom, while on the right we have the opposite: a Founders Edition on top, and an ACX card on the bottom. Note that we didn't test dual Founders Edition cards for two reasons: first, to avoid any hint of bias, we buy all our test video cards at retail, and buying another $500 GTX 1080 Founders Edition just for the sake of running one additional benchmark just didn't work for us, sorry! But more importantly, we can deduce from the data we collected, which you'll see in a moment, that dual Founders Edition cards would in fact be inferior to several of the other setups we tested.

SLI Duos

First, we test our cards at reference settings. Recall that boost levels drop once the GPU hits 80 °C, and when running dual cards, that temperature is much more likely to be reached.


Well, no doubt about it, dual open-air ACX cards rule the roost here. Follow the blue bars in the graph above, and you'll see that this setup leads to the lowest GPU temperatures and therefore the highest performance, despite the lowest fan speeds and lowest noise. The only drawback of this setup is that it heats up the CPU area enough to actually impact our high-powered liquid CPU cooler. A less-capable air-based model could potentially be overwhelmed given the amount of heat being pumped into the case. That's why we always recommend liquid CPU coolers in dual GPU setups. It just takes the guesswork out of the equation. 

We can deduce from these results that even if we'd tested dual Founders Edition cards in SLI, they wouldn't have been all that impressive. The setup with the Founders Edition card in the top position and an open-air card below, which is represented by the green bars, performed quite a bit worse than dual open-air cards. There's really no scenario we can think of where adding a second FE card in the lower position would be preferable. It could be better than an FE card on top and open-air card on the bottom, but it wouldn't be better than the dual open-air setup we tested.  

Frankly, we were a bit surprised that the combo of an open-air card on top and a Founders Edition card on the bottom, represented by the orange bars in the graph above, didn't perform better in this test. Despite a scenario where it wasn't inundated by lots of waste heat from the card below, the top-mounted ACX card ran hotter in this test than it did when we tested dual ACX cards. Let's see if that holds true when we push the clockrates up...


Now this is where things finally start to get interesting. Thus far, the Founders Edition hasn't really proven its worth (or justified the higher price that Nvidia set for it!). But when pushed to the limit, our dual open-air ACX cards start to show their limits. In this test, the top card is now hitting 84 °C, which leads to a massive thermal throttle. This is despite the fact that its fan is running at 100%. The card is maxed out, but it's not providing maximum performance. You can see that in the framerates for the dual ACX setup (again, follow the blue lines). It's the slowest, loudest setup, and it's not doing great things for our CPU either. In other words, choosing matched open-air ACX cards is actually the worst choice if you're running dual overclocked GTX 1080 GPUs! Replacing the top card with a Founders Edition model doesn't help matters much, as that card will also throttle significantly, while running its fan at 100%. The best solution is to have a Founders Edition card below, which allows both it and the ACX model above to level off at 80 °C using an 80% fan level, which offers the best combination of performance and noise levels.

Ultimately, the results are so tight here that one little change to the test setup could flip the outcome entirely. The use of a larger open-air card with dual 100mm fans or triple 80mm fans might put the open-air setup ahead, whereas a smaller ATX case with far less airflow (i.e., most ATX cases) would put even more of a hurt on the open-air cards. And remember, we're using a liquid CPU cooler that really isolates the CPU to a great extent, but if you were running an air cooler, things would be totally different - not only would the CPU heatsink fill with hot air from the video cards, but it would also block the exit of exhaust air, causing more air to be trapped around the video cards. In other words, there are simply too many scenarios for us to test, but by presenting a number of test setups in this article, we think we've given you something to work with.


Overall, we think it's pretty clear that the Nvidia Founders Edition cooler is competent, but not compelling. It's a safe bet, and it's the model almost every OEM uses, but for performance enthusiasts, it's rarely going to be the best pick. That's especially true with the GTX 1070 and GTX 1080, for which Nvidia charged a premium over aftermarket models to get a reference cooler. In the face of limited early supply, early adopters simply accepted the "tax," and it certainly added to Nvidia's bottom line, but it shouldn't be used to gauge the value of the Founders Edition cooler today. Nearly any open-air model will be superior in terms of thermals, acoustics, and most importantly, performance, even when set to the same clockrates. That being said, in a few instances, we saw where an externally-exhausting model could provide benefits, namely in low-airflow ITX system, where the Founders Edition performed nearly as well while limiting impacts on the CPU, as well as in an overclocked SLI setup, where dual open-air cards simply choke on their own waste heat. In other words, pick the right tool for the right job!

We hope you've learned a thing or two about coolers in this article - we certainly did! If you'd like to build yourself a well-balanced, well-cooled PC, see our do-it-yourself PC Buyer's Guides, updated monthly, and if you're in the market for a video card upgrade, check out our Video Card Buyer's Guide, updated quarterly.

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