Overclocking Coffee Lake

In terms of how you go about over clocking Intel’s latest Coffee Lake CPUs, the method hasn’t really changed compared with over clocking a Kaby Lake CPU. You still have a 100MHz base clock, a CPU multiplier and you need to deal with similar voltage ranges. The difference, of course, is that with more cores, you’ll have to contend with more hit.

 
Core i3 CPUs have brought the biggest change in this respect, where the TDP has risen from 60W for the Corei3-7350K to 90W for the Corei3-8350K, thanks to a doubling in the number of cores.

At stock speed, these CPUs are easily tameable, but we’ve found the 6-core Core i7-8700K draws quite a bit more power than the core i7-7700K, and generates more heat too,which is to be expected when it has 50percent more cores under the heat spreader.

We’ve found 5GHz to be a reasonably easy target for the Coffee Lake CPUs we’ve tested so far. Our Corei7-8700K is an engineering sample from Intel, and we got it up to 5GHz using a vcore between 1.25V and 1.32V, depending on the motherboard; more recent EFIsonZ370 board shave seen the required voltage to be closer to the former figure.

However, we’ve heard from a number of retailers that 5GHz isn’t always possible on the Core i7-8700K, with4.8GHz being a more realistic frequency on some retail samples. Temperatures quickly become an issue too, since Intel is again using thermal paste and not solder between the CPU core and heat spreader. However, we’re also dealing with more cores, and there fore many more fast-switching transistors, concentrated in the same amount of space as a Kaby Lake CPU package.

Our Core i3-8350K sample, however, was a retail CPU, so we’re a little more confident about its performance and over clocking head room being indicative of other retail samples.

That’s is great news, as we managed to get our chip to 5.1GHz, albeit with a fairly high vcore of 1.34V. Still, our all-in-one liquid cooler easily dealt with the temperature, and none of the cores went beyond 85°C.

Set XMP profile

Which ever Coffee Lake CPU you’re using, start by applying the XMP profile in your motherboard’s EFI to set the correct memory speed; in our case, this happened to be 3200MHz.

This setting will also apply the correct memory timings. The XMP profile setting is usually found in the Extreme Tweaker section on Asus motherboards, the MIT section on Gigabyte motherboards or the OC section on MSI motherboards.

Set vcore

We’ll be applying a fairly simple fixed vcore in this guide, but you can conservatively experiment with adaptive and offset modes if you want to reduce power consumption as much as possible.

We haven’t needed more than1.35V to get either of our K-series CPU samples to 5GHz, so that’s a good starting point from which to work back. You might need to switch the EFI’s CPU voltage setting to manual mode in order to set the vcore.

Set multiplier

Find the CPU core ratio setting and put 48 into the field. We’ll start with 48, and then hopefully you’ll be able to raise this figure to 50, but aim for 4.8GHz first, incase the CPU buying lottery didn’t land you with a particularly overclockable chip.

Apply loadline calibration

While we only had to set the correct frequencies and vcore on the MSI and Asus motherboards we tested, Gigabyte’s boards seemed to love a helping of loadline calibration, which suggests they suffer from vdroop. However, they then required the lowest vcore on test, as well as having very frugal power consumption.Consider applying loadline calibration if you’re using a Gigabyte board, or if you’re having problems getting your CPU to 5GHz.

Using software instead of the EFI

Alternatively, you can use your motherboard’s software to overclock the CPU from within Windows, which can save you a huge amount of time. However, it’s still worth applying the XMP profile in the EFI. Makesure you tell the software to apply the overclock to all cores. There’s usually fan control software too, which can help you to fine-tune your system’s fans to keep your overclocked CPU cool without making too much noise.

Stress testing

There are two parts to stress testing. Firstly, you need to make sure your CPU cooler can handle the temperatures from the increased frequency and voltage, and then you need to assess whether the voltage is high enough for the overclock tobe stable. Start by downloading Core Temp (www.alcpu.com), CPU-Z (www.cpuid.com) and Prime 95 version 26.6 (www.mersenneforum.org).

Check your overclock has been applied using CPU-Z, and use CoreTemp to monitor
temperatures. Run the smallfft test in Prime95, and check the core temperatures while it’s running. Any temperature above 85°C is at adwarm for an everyday overclock, especially if you’re testing in colder months. A15-minute run of Prime95 can be a good indicator of stability too. If your temperatures are acceptable, it’s also worth running the video encoding and multi-tasking tests in our Real Bench test suite (www.asus.com/ campaign/Realbench) as well as having a few gaming sessions to makesure.

If your system is all stable, head back into the EFI and increase the multiplier a notch. Rerun the benchmark and temperature tests a gain until you encounter stability issues, then knock back the multiplier to the previous stable setting. In our case that was 5GHz for the Core i7-8700K and 5.1GHz for the Core i3-8350K, although your mile age may vary.

Don’t leave the voltage at 1.35V,
Stress-test your CPU, while monitoring the core temperatures, to make sure your overclock is stable
as you can likely cut it back. Dropit by0.02V (from1.35Vto 1.33V), then rerun the benchmarks to test stability. When you encounter issues, raise the voltage again by the same 0.02V amount and retest your system.You should find that you can reduce the voltage to below 1.3V, which will mean your CPU will run cooler, draw less power and be less likely to suffer in the long run.