Overclocking Under Water Cooling
GP102 is particularly sensitive to changes in temperature, so we had high hopes for additional headroom after replacing the stock cooler with Arctic's Accelero Hybrid III-140.
Installing a Closed-Loop All-in-One Liquid Cooler
The first step involved removing the functional backplate. There's nothing hard about this; just turn the screwdriver. But the moment we went to remove the main heat sink, we spotted a warranty seal. You have three choices at this point: rewind your progress to preserve MSI's warranty, punch through the sticker and remove the screw underneath, or come up with your own creative way to work on the Lightning Z board without voiding its factory guarantee.
Arctic's assembly isn't particularly complicated. But we still feared for the integrity of our board. GPU dies aren't protected by an integrated heat spreader like you see on CPUs. Naturally, you have to be exceedingly careful and ensure the water block is placed well before tightening its screws. If you have any doubts, start over. Otherwise, misalignment can have dire consequences.
Then again, we strapped the Accelero Hybrid III-140 to our four GeForce GTX 1080 Tis and several older graphics cards without a single accident. Be careful, but don't panic either.
The backplate is thick, and it employs a beefy thermal pad to help draw heat away from MSI's circuit board (most of which originates from the GDDR5X modules on the card's front side).
Unfortunately, the power supply finds itself completely naked. So, we set a large fan on top of it to keep things cool.
To avoid throttling under load, we used the extreme BIOS. This facilitated stable frequencies and more reproducible testing, allowing us to dial in the most precise settings possible.
When the reported frequency yo-yos between 2040 and 2070 MHz, which one would you rather see? The latter might have only held for 10 seconds before dropping. The former hardly registered in our performance metrics. How about averaging them? It's not easy to decide.
Using the extreme BIOS, though, there's no need to choose. Throttling stops becoming an issue. Here are the maximum frequencies we were able to sustain through the 3DMark Time Spy benchmark:
|Frequencies in 3DMark Time Spy||GPU||RAM|
|Card #1||2088 MHz||1490 MHz|
|Card #2||2100 MHz||1576 MHz|
|Card #3||2075 MHz||1550 MHz|
|Card #4||2075 MHz||1550 MHz|
There's a scant 25 MHz of peak headroom between the best and worst Lightning Z cards in our lab. As for memory, all of our samples overclock pretty well; only the first one fails to cross the 1500 MHz threshold using MSI's default supply voltage.
Moving from the stock cooler to an all-in-one paves the way for a slight speed-up. However, the gains are really quite minimal (25 to 35 MHz higher, at best). Given the extra money you'll spend on a closed-loop liquid cooler, the loss of your warranty, and the risk of causing damage, it'd be foolish for us to recommend the swap. The Accelero, while sufficient for a normal GeForce GTX 1080 Ti, isn't a strong-enough performer to stand out from the Lightning Z's monstrous heat sinks.
To compare, we observed a temperature of 42°C with the all-in-one, whereas it landed around 47°C with the stock cooler and its cooling fans set to 70%.
The screen shot above depicts the best score we obtained with Arctic's Accelero strapped onto MSI's GeForce GTX 1080 Ti Lightning Z. It came from our second sample, with a GPU frequency of 2100 MHz and the memory operating at 1576 MHz. As you can see in Afterburner's log, the frequency doesn't spike or dip at all thanks to the extreme BIOS we used. When the clock rate does drop, it's because GP102 is idling.
Overclock The GPU, Memory, or Both?
Pushing GPU and memory frequencies higher, stably, is our ultimate goal here. But to what end? Should we be pursuing one overclock more aggressively than the other? To answer this question, we benchmarked at stock clock rates, then with the GPU overclocked, next with only the memory overclocked, and finally with both of them cranked as high as they'd go.
Remember that the BIOS is modified, and that MSI ships this card heavily overclocked from the factory.
Pushing the memory 150 MHz higher yields roughly the same gains as a +100 MHz GPU overclock. While the result isn't overwhelming, it is still worth taking; it's free, after all. More important, this shows the value of overclocking the RAM. Three-hundred points is not much for a gamer, but, for an overclocker, it is huge.
Scaling As A Function Of Voltage
This may be hard to believe, but there is nothing to be gained by increasing voltage to Nvidia's GP102. Worse, pushing voltage higher results in more heat output. Under normal circumstances, that means GPU Boost will pull frequencies back sooner than if you just left this setting alone.
If you're using an air or water cooler, our best recommendation is to leave voltage at its default 1.06V.
Understandably, the GPU frustrated us. So we decided to explore memory scaling by applying +80mV to the GDDR5X with a little help from Afterburner. This helped us go from 1550 to 1576 MHz. In order to avoid damaging the memory modules, though, we didn't push any harder at ambient temperatures. We'll exact our vengeance with a cold plate and liquid nitrogen.
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