Overclocking on the Z390 platform is pretty much the same as on the Z370 platform. So if you are familiar with that, overclocking your Core i9-9900K will be pretty easy. Keep in mind while the Core i9-9900K will boost up to 5.0 GHz that is only on a single core. When we are overclocking we are looking for all 8 cores to run at that speed or higher. We are testing on the ASRock Phantom Gaming SLI/ac motherboard so our BIOS settings might differ a little bit from yours.
So in our BIOS the first thing we are going to want to set is the CPU Ratio mode to “All Core” and the “All Core” ratio to what we are going to shoot for. In our case it is 51, which will bring all of our cores to 5.1 GHz. Also if your BCLK is set at “Auto” it is a good idea to set it at “100.00”.
On the same page in the ASRock BIOS you’ll find your power limit and current limit settings. Motherboards have built-in power settings that will actually throttle your CPU if you throw too much power at it. To disable these built-in settings you can max out the “Long Duration Power Limit” and “Short Duration Power Limit”. You are also going to want to max out the “CPU Core Current Limit”, typically 255.50 is the max you can set here.
In your Voltage and power settings you are going to want to have a set CPU VCore voltage, we went with 1.35V. You may also want to test different load-line calibration settings.
So with these settings we were able to achieve an overclock of 5.1 GHz across all eight cores of the Core i9-9900K.
This was a completely stable overclock, but be sure you have appropriate cooling (we used an NZXT Kraken X52) as during load our CPU temperate averaged around 84C. Here are some test results with our overclocked settings.