Overclocking E8400 voltage question

[yughi]

motherboard: gigabyte ep45-ds3l
memory: g.skill 2x2gb pc6400 4-4-4-12
video: geforce gtx 260/216 core overclocked to 675/2200 (same speed as stock gtx 280)
thermal paste: tuniq tx-2 (no re-greasing every 6 mos unlike arctic silver 5)
winxp sp2

e8400 overclocked to 4.0ghz 9x445 @ 1.35v
loosened ram to 5-5-5-15 and 1:1 ratio @ 2.02v
pci-e to 100mhz
everything else on "auto"
using realtemp 2.70 idle 36c/max load 59c (prime95)

original voltage 1.4225v and a few weeks later, lowered voltage to 1.35v prime95 stable.
in my case the e8400 needed time to "break in" before attempting to lower the voltage.
not all motherboards and not all e8400's will react the same way. depends on your set-up.
intel p45 mobos are excellent in overclocking.

 

[Percussionist]

Originally posted by: Psynaut
I got my e8400 stable at 4.0 GHz for 8 hours on Prime 95 by setting my core voltage in the Bios to 1.4225 volts, which I know is a bit beyond the safe zone. The thing is that CPU-Z, CPUID and Everest all show my voltage without a load as 1.24 volts and under load as 1.22 volts.

Now I am new to overclocking but I think I understand that Vdroop is the difference between the 1.22v and the 1.24v number (please correct me if I am wrong), so I know that drop is to be expected. What I don't know for certain is which voltage I should be using for overclocking if I want to stay below the intel recommended 1.3825v or the 1.4v max recommended by most overclockers, nor the reason for the wide disparity between the number I set in the Bios and the 'No-Load' voltage in CPU-Z. As a sidenote I raised my MCH voltage from 1.25 to 1.41 to get a stable overclock, I hope this is within a safe range.

At 4.0 GHz my cores run at 63c and 64c. At 3.8GHz, with a bit less voltage they run at about 61c - 62c. My rig is in my sig.

For overclocking which voltage do I use? I would appreciate any other observations as well.

*edit: Both my heatsink and my CPU are lapped.

@Psynaut: I'm wondering if you ever got a definitive answer to your voltage question. I'm doing some experimenting with overclocking my system and have the exact same question. I've been able to push my CPU to a relatively stable 3.9GHz (6+ hrs in Prime95) with a setting of 1.3625V in my BIOS while reading 1.312V-1.328V in CPU-Z. I'd love to be able to hit that 4GHz milestone but don't want to fry anything in the process: it's just not worth it to me! In any case, I'd love to hear what you've found out, if anything, since your original post. Thanks in advance!

 

[udneekgnim]

Originally posted by: Percussionist

Originally posted by: Psynaut
I got my e8400 stable at 4.0 GHz for 8 hours on Prime 95 by setting my core voltage in the Bios to 1.4225 volts, which I know is a bit beyond the safe zone. The thing is that CPU-Z, CPUID and Everest all show my voltage without a load as 1.24 volts and under load as 1.22 volts.

Now I am new to overclocking but I think I understand that Vdroop is the difference between the 1.22v and the 1.24v number (please correct me if I am wrong), so I know that drop is to be expected. What I don't know for certain is which voltage I should be using for overclocking if I want to stay below the intel recommended 1.3825v or the 1.4v max recommended by most overclockers, nor the reason for the wide disparity between the number I set in the Bios and the 'No-Load' voltage in CPU-Z. As a sidenote I raised my MCH voltage from 1.25 to 1.41 to get a stable overclock, I hope this is within a safe range.

At 4.0 GHz my cores run at 63c and 64c. At 3.8GHz, with a bit less voltage they run at about 61c - 62c. My rig is in my sig.

For overclocking which voltage do I use? I would appreciate any other observations as well.

*edit: Both my heatsink and my CPU are lapped.

@Psynaut: I'm wondering if you ever got a definitive answer to your voltage question. I'm doing some experimenting with overclocking my system and have the exact question. I've been able to push my CPU to a relatively stable 3.9GHz (6+ hrs in Prime95) with a setting of 1.3625V in my BIOS while reading 1.312V-1.328V in CPU-Z. I'd love to be able to hit that 4GHz milestone but don't want to fry anything in the process: it's just not worth it to me! In any case, I'd love to hear what you've found out, if anything, since your original post. Thanks in advance!

this seems like one hell of an old thread to bump for a first post, but Intel specified max Vcore for 45nm CPUs is 1.3625. anything above is supposed to lower the life expectancy of your CPU. however, some people are not even comfortable with a Vcore above 1.3 volts. anyways, CPU overclocking should be considered a tradeoff between increased performance versus CPU life expectancy.

as long as CPUZ reads 1.3625 volts or below, your CPU should be fine per Intel's spec. be sure your CPU PLL and CPU VTT isn't set too high as well. Most people keep CPU PLL at 1.5V and I think 1.36 or below for VTT is a good rule of thumb.

 

[Percussionist]

Originally posted by: udneekgnim

this seems like one hell of an old thread to bump for a first post,

Heh, yeah I know; I was just interested since someone else had been asking about the very issue I happened to be dealing with!

Originally posted by: udneekgnim

as long as CPUZ reads 1.3625 volts or below, your CPU should be fine per Intel's spec. be sure your CPU PLL and CPU VTT isn't set too high as well. Most people keep CPU PLL at 1.5V and I think 1.36 or below for VTT is a good rule of thumb.

Thanks for the clarification; this helps a lot. In pushing to 4.0GHz I find that setting my vCore voltage to 1.40625V in BIOS results in a 1.344-1.360 reading from CPU-Z and SpeedFan so I'm thinking (hoping) I'm in the clear. I realize that may be pushing it for the life expectancy of the proc and may not keep it there in the long run. Mostly I've just been wanting to find out if (a) this particular proc could hang and (b) if I could find the right tweaks to make it happen. Thanks again for the help!

 

[Tempered81]

Originally posted by: Percussionist
I'd love to be able to hit that 4GHz milestone but don't want to fry anything in the process: it's just not worth it to me! In any case, I'd love to hear what you've found out, if anything, since your original post. Thanks in advance!

I asked around as XS and got some answers about fried E8400's:
http://www.xtremesystems.org/f...howthread.php?t=211803

 

[Percussionist]

Originally posted by: jaredpace

Originally posted by: Percussionist
I'd love to be able to hit that 4GHz milestone but don't want to fry anything in the process: it's just not worth it to me! In any case, I'd love to hear what you've found out, if anything, since your original post. Thanks in advance!

I asked around as XS and got some answers about fried E8400's:
http://www.xtremesystems.org/f...howthread.php?t=211803

Thanks for the link; looks like people have driven their E8x00's pretty high with relative success. I've got mine at 4GHz with a vCore of 1.36 and temps are in the low 60's so I think I'll try it again with a lower voltage (previous Prime95 run went 8+ hrs before I stopped it). I'm with you though: it seems that the 1.4 "safe zone" is a relatively low estimate.

I'm still a bit hazy regarding VTT and PLL. I've done some reading on other sites, including Intel's own data sheets (lots goes over my head), and have been trying to relate the info to what I see in my mobo's BIOS. The only voltage settings I've got listed are for DDR2, PCI-E, FSB, MCH, and CPU. I'm still not sure what VTT and PLL refer to. Forgive me if this seems basic but I'm relatively new to tweaking systems and am eager to learn as much as possible. Thanks again for your help.

*Edit: I've seen screenshots of other BIOS's that include a setting for CPU PLL Voltage but mine doesn't so I'm assuming I'm not able to change it with my mobo (ep35-ds3l).

 

[Tempered81]

vtt=fsb also, you don't have pll control.

when you measure 1.36v, is that bios, or cpu-z?

 

[Percussionist]

Originally posted by: jaredpace
vtt=fsb also, you don't have pll control.

OK, cool; thanks.

Originally posted by: jaredpace
when you measure 1.36v, is that bios, or cpu-z?

That's what CPU-Z (and SpeedFan) tells me; in BIOS I currently have the voltage set @ 1.4. But this kind of goes back to my original question: which is best for a [somewhat] definitive reference point?

[/quote]

 

[Tempered81]

Originally posted by: Percussionist

Originally posted by: jaredpace
when you measure 1.36v, is that bios, or cpu-z?

That's what CPU-Z (and SpeedFan) tells me; in BIOS I currently have the voltage set @ 1.4. But this kind of goes back to my original question: which is best for a [somewhat] definitive reference point?

Well cpu-z reads the actual cpu voltage better than most programs, and it's realtime. It's close to the actual voltage. Here is an example of 1.392v Vcore "Actual".
http://img110.imageshack.us/img110/3916/41291517ql2.png
The bios may have been set to somewhere around ~ 1.44 - 1.46v to achieve this.

 

[Percussionist]

Excellent; I think this leaves me with a little headroom to either drop my vCore and keep the CPU @ 4GHz or see if I can push beyond that clock speed (although I'm pretty happy with the extra 1000MHz as it is).

jaredpace, you've been extremely helpful; hope to run into you some more on here (and elsewhere, perhaps). Thanks!

 

[Tempered81]

yah same to ya. good luck