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Thread: Help me OC my E8400




  1. #11
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    Default Re: Help me OC my E8400

    Okay, so when I adjust the cpu and mch reference voltages before adjusting vtt. Sounds simple enough with trial and error. How will I know when I have the cpu and mch ref adjusted correctly? Will it become stable or will that only come after i find the right vtt? I have been reading that vtt is just going to allow the fsb to be pushed farther so as long as I have a high enough vtt to support 455fsb then all I need to do is get the mch and cpu ref adjusted correctly right?

  2. #12
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    Default Re: Help me OC my E8400

    I found cpu ref, mch ref and vtt work in tandem with each other. You may have to find another gtl ref combo for each level of vtt. Based on my experience, the higher you push your vtt, the more likely I needed to lower my gtl ref voltages. I also found that with my two e8400, they liked to have the mch ref voltages lower than the cpu ref voltages. YMMV. Record your combinations in a spread sheet to help facilitate the process.

    edit: For got to address this. You will know if your mch and cpu ref's are correctly when you can pass your stability test of choice.
    1) Gigabyte EP45-UD3P (rev 1.1, bios F9) E8400 @445x9@1.2625v bios, TRUE 120, Scythe UltraKaze 44cfm, 4x2gb GSkill 8500, Visiontek 3870, Corsair TX850, Antec 900, Win7-64 Home.
    2) Gigabyte EP45-UD3P (rev 1.1, bios F9) E8400 @500x8.5@1.2875v bios, TRUE 120, Schythe UltraKaze 44 cfm, 4x2gb Buffalo FireStyx 8500, XFX 5770, Corsair AX850, CM Scout, WinXP Pro/Win 7-64 Home.
    3) Gigabyte P55A-UD4P (rev 1.0, bios F5) i5 750 @190x20@1.30625v bios, CM Hyper 212+, 4x2gb G.Skill Ripjaw 1600, 7900GS, Corsair TX750, CM Scout, Win7 Pro-64.
    4) Asus P8Z68-V Pro (bios 0801), i5-2500K @44x100@1.248v cpuz, Megahalem rev.B, 4x4gb GSkill Sniper 1600, Corsair AX850, Antec 902, Corsair Performance 3 128GB, Win7-64 Home.


  3. #13
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    Default Re: Help me OC my E8400

    Awesome, thanks for the replies friends. I hope to keep getting this kind of support as my other favorite forums have severely let me down.

    Seems I have got the FSB stable at 455mhz now. I kept vtt at 1.2v and the first combination of cpu ref and mch ref I tried was CPU Ref at 0.715v and MCH ref at 0.700v and that got the bus stable. I ran prime for 24 hours and it was still running great. Now tonight I will bring the multi back up to 9x and run prime until tomorrow afternoon and see if the CPU is stable there or if I need to adjust the voltages again.

    Once again, THANKS for the help.

    I just ask that you continue to help me until I reach my personal goal, which is a the highest safe 24/7 oc I can get. I am really hoping for around 4.5ghz. Higher would be amazing but Id really just like to get it to 4.5

  4. #14
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    Default Re: Help me OC my E8400

    Ok, well I need some advice. I got the FSB stable at 455 with the voltages posted above. I then ran prime95 overnight with the multi at 9x and all went well. I then bumped up the FSB to 475 with the same voltages and lowered the multi to 6x to test the FSB stability again. The bus was stable after 12hrs of prime so I raised the multi back to 9x again and cranked the vcore up to 1.3v to check for CPU stability. The CPU was not stable but interestingly, core0 failed 7 minutes in and core1 was running fine 12hrs later. From what I read it sounds like a gtl voltage is not right but I wanted to check here before I continue.

    What do you suggest I do?

  5. #15
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    Default Re: Help me OC my E8400

    For 475 x 9 = 4275mhz, you're going to need more cpu voltage than 1.30v. However, start increasing your vtt from 1.20v and see if prime can run longer before failing. If it runs longer, then increasing the vtt and cpu voltage is probably the route to go before making any changes to gtl.
    1) Gigabyte EP45-UD3P (rev 1.1, bios F9) E8400 @445x9@1.2625v bios, TRUE 120, Scythe UltraKaze 44cfm, 4x2gb GSkill 8500, Visiontek 3870, Corsair TX850, Antec 900, Win7-64 Home.
    2) Gigabyte EP45-UD3P (rev 1.1, bios F9) E8400 @500x8.5@1.2875v bios, TRUE 120, Schythe UltraKaze 44 cfm, 4x2gb Buffalo FireStyx 8500, XFX 5770, Corsair AX850, CM Scout, WinXP Pro/Win 7-64 Home.
    3) Gigabyte P55A-UD4P (rev 1.0, bios F5) i5 750 @190x20@1.30625v bios, CM Hyper 212+, 4x2gb G.Skill Ripjaw 1600, 7900GS, Corsair TX750, CM Scout, Win7 Pro-64.
    4) Asus P8Z68-V Pro (bios 0801), i5-2500K @44x100@1.248v cpuz, Megahalem rev.B, 4x4gb GSkill Sniper 1600, Corsair AX850, Antec 902, Corsair Performance 3 128GB, Win7-64 Home.


  6. #16
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    Default Re: Help me OC my E8400

    A general guideline:
    VTT should be set at least 0.05 - 0.10 volts lower than CPU Vcore when overclocking.

    VTT up to about 1.35 or so is not excessive when your CPU Vcore is 1.40 volts or higher.
    Increasing VTT often helps with stability if there are errors when running stress testing programs.
    Ideally you'll use the lowest possible VTT voltage setting.

    With higher overclocks, MCH Core voltage might need to be bumped a bit higher.
    Q9650 @ 4.10GHz [9x456MHz]
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  7. #17
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    Default Re: Help me OC my E8400

    Okay, well I am at work atm. Tonight when I arrive home I will increase Vcore and MCH core. I dont think I will have to worry about the MCH voltage too much at 1.3ish since its watercooled. I will do that and bump vcore up to maybe 1.35v and stress test again overnight with the 9x multi again. If that doesnt help I will raise vtt, and test the bus over again with the gtl voltages to see if thats still stable. Once I get that stable if needed then I will raise the multi again and try again with raised vcore and mch core. It might take between 1 and 5 nights to post back depending on how many stress tests I need to run to get to that point.

    Again THANKS for the help. I am learning so much.

  8. #18
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    Default Re: Help me OC my E8400

    Oh and I have been reading that different BIOS revisions affect overclocking performance. I got to 3.8ghz on F9, then went to F11 when I got all the new watercooling parts. Now I see that F12 is out and I was wondering if anyone knows what the differences in the revisions are and if there are overclocking differences. I cant even seem to find a general change log or bios history file. thanks.

  9. #19
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    Default Re: Help me OC my E8400

    Dont be scared to bump up VTT or PLL, I use 1.59 PLL for 24/7 and no degradation at all (some go as high as 1.75 but I wouldnt do that for 24/7).
    If one cores fails it would need more vCore (sometimes up one notch VTT).
    P45-UD3P 1.0 F10i E8400@550x8 max stable OCZ Blade LV 2x2gb 1150@1350 2v max stable

  10. #20
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    Default Re: Help me OC my E8400

    Quote Originally Posted by D-Rock View Post
    I dont think I will have to worry about the MCH voltage too much at 1.3ish since its watercooled.
    Remember you are only using 2 sticks of ram. You don't have to raise your MCH voltage that much. When profJim mentioned, "with higher overclocks, MCH Core voltage might need to be bumped a bit higher", that was based on your mch core being at 1.20v. I suspect 1.22v-1.26v, might be good enough for you. YMMV.

    If I were you, I would bump the mch core up to 1.22v-1.24v, bump vtt up a step or two, and then bump your vcore up to what you feel comfortable with 1.35v+. Then start bumping your vtt some more. If those don't work, then play with your gtl refs.

    All the best.
    1) Gigabyte EP45-UD3P (rev 1.1, bios F9) E8400 @445x9@1.2625v bios, TRUE 120, Scythe UltraKaze 44cfm, 4x2gb GSkill 8500, Visiontek 3870, Corsair TX850, Antec 900, Win7-64 Home.
    2) Gigabyte EP45-UD3P (rev 1.1, bios F9) E8400 @500x8.5@1.2875v bios, TRUE 120, Schythe UltraKaze 44 cfm, 4x2gb Buffalo FireStyx 8500, XFX 5770, Corsair AX850, CM Scout, WinXP Pro/Win 7-64 Home.
    3) Gigabyte P55A-UD4P (rev 1.0, bios F5) i5 750 @190x20@1.30625v bios, CM Hyper 212+, 4x2gb G.Skill Ripjaw 1600, 7900GS, Corsair TX750, CM Scout, Win7 Pro-64.
    4) Asus P8Z68-V Pro (bios 0801), i5-2500K @44x100@1.248v cpuz, Megahalem rev.B, 4x4gb GSkill Sniper 1600, Corsair AX850, Antec 902, Corsair Performance 3 128GB, Win7-64 Home.


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