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Intel Core i7-5960X Underwater: Can a Custom Loop Raise the Ceiling?


CORSAIR Technical Marketing
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When we first took a look at the Intel Core i7-5960X octal-core processor based on Intel’s Haswell-E architecture, we found a processor that seemed to be almost entirely limited by voltage and cooling. The i7-5960X has a staggering large 356mm² die, nearly twice the size of the die inside Intel’s Devil’s Canyon i7-4790K. It’s also soldered to the heatspreader instead of using TIM. What all of this comes down to is lower heat density and better heat transfer. Haswell-E was made for liquid cooling.

We tested the i7-5960X here first under a Hydro Series H100i with fans set to push-pull and were consistently capped at 4.4GHz. Three chips hit 4.4GHz with 1.35V; the fourth needed only 1.3V but was still unable to do 4.5GHz. Load temperatures under OCCT were in the mid-80s, and the H100i was running at full bore.

But recently we upgraded the Yamamura 750D build to feature the i7-5960X.

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The consensus has historically been that a custom liquid cooling loop will always outperform an all-in-one liquid cooler. The EK Supremacy EVO waterblock we used costs almost as much as a Hydro Series H80i on its own, let alone the D5 Vario pump and all copper radiators. Yamamura has a ridiculous amount of heat capacity.

Does going under custom cooling afford us any more headroom? Can we hit that 4.5GHz point?

Actually, no.

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The i7-5960X is already pushing 300W on its own at 4.4GHz, requiring a massive boost in voltage just to hit that point.

Despite a massively powerful pump, a cumulative 120mm x 840mm of radiator surface area, and an expensive, high-performance waterblock, the voltage required to hit 4.5GHz pushes the i7-5960X essentially past its breaking point.

We’ve seen this on other processors, but basically there’s a point where the processor simply generates more heat than can be transferred to the waterblock. When you’re dealing with something like a GPU that has no lid, lower heat density, and nearly direct contact with the waterblock, you can get a tremendous performance boost by putting it under water. There’s very little impeding heat transfer from the die to the cooler.

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But CPUs are different. Heat density is higher, and direct contact isn’t possible (unless you de-lid a Haswell/Devil’s Canyon). It’s respectable that the i7-5960X can be dissipating ~300W before it runs into a wall, but it does hit that wall. The result is thermal performance under a custom loop that parallels the thermal performance you might see under a closed Hydro Series H110i GT.

Custom loops like Yamamura are beautiful, but with high performance closed loop coolers and brackets like HG10 on the market, they’re increasingly difficult to justify. Does putting an i7-5960X under water make sense? Absolutely. But under a custom loop? That’s a much harder sell.

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