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z270 BCLK Overclocking

This is for all overclockers who want to overclock the BCLK. Just know before reading this that overclocking the BCLK is a very miniscule gain in performance and can cause instability with your system and devices. Raising the BCLK increases the CPU, Uncore (cpu cache), Memory, PCIe and DMI bus clocks.

With an i7-7700k you should be able to hit 200 - 300 BCLK so let's try for 200 BCLK. Since the i7-7700k turbos to 4.5GHz I'll give it a 100MHz overclock to 4.6GHz to work evenly with the Core Ratio.

1) In the bios on the Extreme Tweaker tab set the AI Overclock Tuner to Manual.
2) Enter in 200 for the BCLK or use the + and - keys, at the top of the Extreme Tweaker Tab you now see the clocks in yellow have doubled so we will cut the Ratios in half.
3) Scroll to CPU Core Ratio, sync all cores and enter in 23.
4) Scroll to CPU Cache Ratio and enter in 21 for Min. and Max.
5) Scroll to Dram Frequency and select your original ram speed.
6) Scroll to CPU Core/Cache voltage, 1.20v should work well or you can let it on auto.
7) In Tweakers Paradise the first setting at the top is the FCLK, set the FCLK to 800MHz which should be default.
😎 F10 and Enter to save and exit.

What we did was overclock the BCLK to 200, gave the i7-7700k a 100MHz overclock to 4.6GHz and took the System Agent Clock from default of 800MHz up to 1600MHz.

I use HWInfo to record clocks, voltages and temps.

The Bus clock is the BCLK at 200 in red.
BCLK 200 x FCLK 800 = System Agent Clock 1600Mhz in blue.
BCLK 200 x CPU Core Ratio 23 in green = CPU Core Clock 4600MHz
BCLK 200 x Uncore Ratio 21 in green = Ring Clock 4200MHz which is the CPU Cache Clock.
Vcore is at 1.20v


For 300 BCLK I had to overclock the cpu further and lower the ram speed. This is for a 5.1GHz cpu overclock, if your cpu is not capable or you don't have sufficient cooling stop here and stick with 200 BCLK or you can try with lower ratios.

Back in the bios......

1) Set the BCLK to 300.
2) Set the CPU Core Ratio to 17.
3) Set the CPU Cache Ratio to 16 Min. and Max.
4) Select Dram Frequency 2800MHz, this was the highest frequency I was able to boot with.
5) Set the CPU Core/Cache voltage to 1.35v - 1.45v.
6) In Tweakers Paradise set the FCLK to 400.
7) F10 and Enter to save and exit.

The BCLK is at 300.
BCLK 300 x FCLK 400 = System Agent Clock 1200MHz.
BCLK 300 x CPU Core Ratio 17 = CPU Core Clock 5100MHz.
BCLK 300 x Uncore Ratio 16 = Ring Clock 4800MHz which is the CPU Cache Clock.
Vcore is at 1.35v.


I'd suggest staying around 200 BCLK, once you have to lower the ram speed you're losing performance. I wasn't able to get much more than 300 BCLK, if you want to try for a higher BCLK please do and post your results. If you have any questions or problems please ask.

Always keep an eye on your temps when overclocking.

Level 12
I wished I had this CPU and board :P. The guide looks very straight forward and easy to understand, thanks for sharing this Nate.

Level 11
I try my best with my 6700k and M9H. I want to get the 7700K to have lower VCORE. as soon I have the new cpu I will call one of you guys for help! I order to achive that in IDLE, today is a nice 26C ambient with 70% humidity, all C state are off and using Alphacool Eisbaer 240 with ML fans. but I know that the small change is minimal but having better bond with the z270 will better!. Thanks Nate I will add your name in my list! these week I will work on my GPU since the weather is very nice to OC

Learn, Play Enjoy!

Hi Itzycharles

It looks like you have a nice overclock already and your temps look great !

You can try for 200 BCLK with your 6700k, it overclocks the BCLK pretty far and should easily do 200 BCLK.

1) Set The BCLK to 200
2) Set the CPU Core Ratio to 23
3) Set the CPU Cache Ratio to 20

Increase the BCLK until the CPU Core Clock reaches 4700MHz and the CPU Cache Clock reaches 4100MHz, then set the Dram Frequency as close to 3200MHz as you can.

Because you raised the BCLK above 200 the ram speed won't have even numbers.