Overclock intel 2500k with P8Z68-V LX board

Overclocking method of Dual core i5 CPUs is same to that of 3 CPUs, anyways you can go through the below things to understand and perform overclocking:

Setup:
First go into your system’s BIOS and load defaults, make sure that you are saving the changes before exiting. Once you are done just reboot your system and enter the BIOS setup utility again for disabling power saving features. You should leave all other settings on auto, if you want then you can turn off any start-up slash screens if you are having. Turning off start-up slash screens is not recommended but I think doing that is a better idea as far as safe overclocking is concerned. You can also disable any “integrated peripherals” which might not be in use, if at all after changing these settings your motherboard fails to post then you can reset the CMOS. There are different ways of resetting the cmos but the easiest one is by taking out the cmos battery from the board. You just have to turn off your system, unplug the power cord, take out the battery, wait for some time, reseat it, plug the power cord and turn on the system. If things are fine after changing the above settings then you can proceed with the below things.

CPU frequency:
Before overclocking CPU you should know how fast your CPU can run. The below equation will help you in determining the clock speed of the CPU’s cores:

CPU Frequency = Base Clocks x Multiplier. Here FSB and multiplier will determine the CPU speed,FSB is similar to base clock but there are some key differences. The base clock is said to be the foundation of all the other frequencies that are mentioned further.

QPI Frequency – QPI Frequency is the Intel communication path, there is a direct link (QPI) that will help in increasing efficiency. When you will increase your base clock the QPI speed will get increased along with it.

Uncore frequency – Uncore frequency sets the frequency of the on-die memory controller as well as. Uncore can be set independently but it should be 2:1 of the DRAM speed otherwise in order to do a stable overclocking. If you dint follow this ratio then there are possibilities that your system will not boot. So to get significant performance gains just increase the uncore:dram ratio above 2:1 yields.

Multiplier and Turbo – This is the second factor for determining CPU core speed, multipliers vary from cpu to cpu based on the price/performance. Now a day’s most of the cpu come with a Turbo multiplier, you can check it out after enabling Speedstep option under the CPU settings. You should be carefill while using turbo as it does not shows resultant frequency in BIOS. Just for eg if your default multiplier of CPU is 20 (i7-920) and your baseclock is 200 and you boot your system with turbo enabled, then the bios will lead at 20 x 200 = 4 GHz. Now when you will enter windows then turbo will end up with 21 x 200 = 4.2 GHz. If you are having C-State enabled then one CPU core will get access to a 22 multiplier and will run at 22 x 200 = 4.4 GHz. So here you might be expecting your voltages to run at 4 GHz whereas its kick up to = 4.4 GHz. In such cases you will get BSOD while entering Windows. Hope you understood why is it important to be careful while using turbo and C-State.

Understanding Voltages:
When overclocking there are some voltages which has to be manipulated, I am just listing the important ones.

V-Core – This is related to CPU frequency directly. You will have to increase the v-core as you increase CPU frequency.
QPI voltage/CPU Vtt – Increase QPI voltage is important while increasing RAM speed, this helps in stabilizing your overclock at higher base as well.
VDIMM/DRAM – VDIMM/DRAM is related to RAM memory modules directly, you will have to increase the same while increasing Ram speeds. You must be very careful at this time and not increase it more than 0.5 volts. If you increase it above that then there are chances where you will damage your CPU permanently.
IOH Core Voltage- You can leave this to auto but if the clock is above 200 then you will have to increase it as well, it is recommended to set it to auto.
ICH Core Voltage- You should set this to auto as well as ICH Core Voltage feeds the chip which regulates communication between the peripherals and CPU through DMI.

Once you are completely aware of these voltages then you can proceed further.

Maximizing Bclock Frequency:
Before Maximizing Bclock Frequency you should isolate the bclock to find its stable limit. You will have to manually force a low multiplier for the CPU in order to isolate the bclock. Generally an i5 750 at stock speed runs on a 133MHz bclock and x20 multiplier which brings up a stock speed of 2660MHz (133×20).So if you will be increasing bclock to 200 along with stock x20 multi then it will result in 4000MHz which won’t be safe for now. A safe choice here will be x12 multi for a 200MHz bclock which will result in 2400MHz. In some cases x12 might not work so you can lower the same without worrying about it.

As far as I am aware fastest rated speed for memory on P55 with i5 750 is DDR3-1333, which gives a clock speed of 667MHz.Since in your case you are having a P8Z68-V LX board it will differ. You will have to lower the memory multiplier accordingly to isolate memory from bclock, once you reach to 200MHz bclcok frequency successfully your memory will be 600MHz (DDR3-1200) well within the capability of DDR3.

Now you will have to isolate bclock from the iGPU which is there in Clarkdale CPUs only.If you are having a old version of bios then update the same to get iGPU option in BIOS. iGPU frequency setting is based on default bclock frequency which means if an iGPU frequency is set to 900MHz in BIOS then it will be 900MHz only. Currently there is no software monitoring utility for monitoring iGPU frequency, so you will find it hard to understand. Anyways it for now you just have to isolate it as a variable for overclocking process. If your goal is 200MHz bclock frequency then you will have to lower the set iGPU frequency. Once you you attain your goal successfully then your set iGPU frequency will get actual iGPU frequency of 900MHz.

Bclocking voltages:
You will have to check out 2 voltages that are important, one is VTT and other is IOH. If you are having single PCIe card then set IOH to 1.3V, if you are having one PCIe graphics card then set it to 1.35V. VTT is also known as “CPU VTT” or “QPI/DRAM” and is a crucial voltage adjustment. VTT is fed to the IMC (Integrated Memory Controller) and has impact in overclocking the bclock. VTT Stock value will differ as per the platform and CPU.

When you are done with all these things then reboot your system and are ready for overclocking. Now enter the BIOS and check the CPU temp in temp/voltage monitoring section. If you find the temperature too high then shut down the system and check out the cooling system. If things goes well then you should be able to get 150MHz bclock stability with stock voltages, so you can set bclock from 133MHz to 150MHz.After setting bclock to 133MHz its time for testing highest stable bclock frequency, for testing you will have to download RealTemp, CPU-Z and Prime95.

Testing the stability:
When the windows get loaded successfully then run RealTemp and keep it running so as to check the stability. RealTemp will show your CPU’s core temp real-time and distance to TJ Max, just make sure that you are not exceeding TJ Max. After running RealTemp start CPU-Z to make sure that the overclocked settings are applied properly and running at expected speed. You can check out the expected CPU frequency in CPU tab, and memory speed in memory tab. After checking these things you can start Prime95 and run test for a short time say 5. Once the test gets over successfully then reboot your system and enter BIOS. Now you can raise the bclock by 10MHz, reboot your system run Prime95 test again. You can raise bclock by 2MHz until you reach desired bclock and pass your stability test. If the Prime95 test fails at any moment then you can try Raising CPU VTT voltage by +0.2V and proceed with the test. You should stop increasing bclock and CPU VTT voltage when you reach desired bclock and max CPU VTT voltage successfully passing stability test.