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View Full Version : Help overclock/volt mod my 8800 GT sli


Van_Dammesque
01-24-08, 08:56 AM
I have two 8800 GT (PoV) in Sli and the max stable overclock (Ati tool artefact scanner showed no errors for 13 hours) is 695/1660/975(x2), now my loaded temps are at worst 46 C! (since it is watercooled, check this build http://www.nvnews.net/vbulletin/showthread.php?t=105791)

I believe I have much more to come from these cards so my questions are:
How do I mod the voltage bios for the core (I think you use NiBiTor.v3.0a right?), how do I do it when the cards are in SLi, and can it be done from windows SAFELY? What is the max voltage core the GT's can take?

Has anyone else done this and what are the results?

It'll be interesting hearing from you guys, thanks.

Feyy
01-24-08, 01:13 PM
Its really easy to vmod the 8800GT's using nibitor. You simply go to the Voltage Table Editor and select the voltage you want (max you want is 1.3v idle because ocp(over current protection) kicks in around about there.) Once thats done go to VID Mode and select the new voltage there. Make sure the one you change is the one marked green (3D Voltage). To test if ovp will kick in run AquaMark3, right before the score displays, the current spikes and you can tell if ocp is holding you back.


Then simply save the bios and flash it, and keep pushing till you reach its limits. If you want further voltage you would need to do a ocp mod which means some soldering work.

I don't know how that works in regards to SLI because i have never used SLI but both cards will run at same speed.
So find the max stable overclock for both. And then apply it to one card. Then when you put the 2nd card in for SLI it should force that card to run the same overclocked settings (just make sure both cards are flashed with vmod and max stable overclocks) :D

ATOJAR
01-24-08, 03:21 PM
Im just in the middle of stress testing a bios voltage mod as i type! modded the bios voltage from the stock 1.05v to 1.1v ... so far ive managed to get the clock core to 756MHz ... just testing the the memory & shaders! .... with stock voltage i can get to 738MHz clock core & 1728MHz shader clock!

Im stress testig with ATItool.

Feyy
01-24-08, 04:48 PM
Im just in the middle of stress testing a bios voltage mod as i type! modded the bios voltage from the stock 1.05v to 1.1v ... so far ive managed to get the clock core to 756MHz ... just testing the the memory & shaders! .... with stock voltage i can get to 738MHz clock core & 1728MHz shader clock!

Im stress testig with ATItool.

Very nice, if you keep pushing voltage you will easily break 800mhz+ on core, ive seen loads of people do it. However if your looking for a 24/7 overclock on your GT then i recommend stress testing with "Fur" http://www.ozone3d.net/benchmarks/fur/

Use settings stability test, no fullscreen(unless your SLI) 1280x1024 and 2xMSAA. Monitor temps carefully and give it 15 minutes atleast. This one really beats down hardcore on your card, it's the only true GPU stress test imo.

ATOJAR
01-24-08, 06:02 PM
What the max safe voltage for a GT?

Feyy
01-24-08, 07:37 PM
You won't get past 1.3vish anyway because of ocp and i'm not sure how far the bios vmod works either. Highest on air would be 1.4v, on water you could push up to 1.6v with ocp mod but you gotta be careful. Also as a hint: some people can push voltage up to
1.6v on load(with hardmods) and have no problems with card shutting down because of ocp, so just try your look and see how things go.

Revs
01-24-08, 07:42 PM
Good thread you guys. I've been meaning to v-mod my GT for a while now. might give it a go this weekend.

john19055
01-24-08, 07:42 PM
Can You overclock the voltage with the 8800GTS 640mb like the 8800GT ,I know I can set the voltage to a higher level ,but do not know if it will be the actully voltage I set it at ,Has anyone overclock the voltage with nibitor on a 8800GTS 640mb and it work.

Feyy
01-24-08, 07:44 PM
Can You overclock the voltage with the 8800GTS 640mb like the 8800GT ,I know I can set the voltage to a higher level ,but do not know if it will be the actully voltage I set it at ,Has anyone overclock the voltage with nibitor on a 8800GTS 640mb and it work.

I tried it with mine, obsolutely no effect. It wasent until i saw a guy get over 800mhz on core with his 8800GT and biods vmods that i realised it only works with the GT. For all other 8800 series cards you need hardmodes with soldering and resistors :(

Van_Dammesque
01-25-08, 08:57 AM
Thanks for the replies! Have used the NibiTor program and have the voltage upto 1.1V and that has allowed me to go past the previous barrier of 695 stable, now testing at 725 core and will continue to push it. (it is also excellent for the shader clock too!)
From what I have read: to go past 1.1 V you have to start editing Hex values, may push for 1.2 V, any precise guides to do it in NibiTor?

For SLI the nvflash command is something like this:
nvflash -5 -6 -i0 newbios.rom
and
nvflash -5 -6 -i1 newbios.rom
where -ix selects which adapter to flash (i.e. -i0 is the first card and -i1 is the second.)
Use the command
nvflash -a
to see which adapters the program can see (should read 0 and 1 adapters)

Revs
01-25-08, 09:08 AM
Out or intetest, what is the stock voltage of the GTS512? The reason I ask is it is the same core but seems to OC alot higher on that card. Is this due to a higher voltage?

ATOJAR
01-25-08, 10:33 AM
Thanks for the replies! Have used the NibiTor program and have the voltage upto 1.1V and that has allowed me to go past the previous barrier of 695 stable, now testing at 725 core and will continue to push it. (it is also excellent for the shader clock too!)
From what I have read: to go past 1.1 V you have to start editing Hex values, may push for 1.2 V, any precise guides to do it in NibiTor?

For SLI the nvflash command is something like this:
nvflash -5 -6 -i0 newbios.rom
and
nvflash -5 -6 -i1 newbios.rom
where -ix selects which adapter to flash (i.e. -i0 is the first card and -i1 is the second.)
Use the command
nvflash -a
to see which adapters the program can see (should read 0 and 1 adapters)

Weird how you can only reach 695MHz on the clock core! ... the overclocks in my sig are all at stock voltage!

Van_Dammesque
01-25-08, 12:10 PM
Weird how you can only reach 695MHz on the clock core! ... the overclocks in my sig are all at stock voltage!
I dunno, the cards were 600 stock and I notice you have a nice BFG OC2!

ATOJAR
01-25-08, 01:00 PM
I notice you have a nice BFG OC2!

Actully it wasent ..... it was a BFG OC(not the OC 2 version) ... i just flashed it with a OC 2 version BIOS. :)

So in theory yes now its a OC 2 version.

Feyy
01-25-08, 01:06 PM
From what I have read: to go past 1.1 V you have to start editing Hex values, may push for 1.2 V, any precise guides to do it in NibiTor?


Try push for 1.2v with bios vmod before you start going into hex values, it should work.

Van_Dammesque
01-25-08, 05:13 PM
Max overclocks now are:
745/1795/990 @ 50 C

had a quick look at NibiTor and flash to 1.15 V tomorrow and see what happens!

Revs
03-23-08, 12:07 PM
Finally got round to soft-modding my cards a couple of days ago. I downloaded the RSSCM.rom and it works really well.

The clocks in the .rom were a little on the low side, so after some testing using FurMark and Crysis I settled on 725/1750/950 as my normal clocks. It was stable at 780/1880/980 but it was getting damn hot and I don't like pushing the cards so much for normal use.

Everthing you need is on the links below. The mod sets the memory timings a little looser as to achive higher memory clocks, ups the core voltage to 1.1v and raises the clocks. Apparently the stock memory timings are a little too tight for the memory chips, that's why they don't OC well.

http://www.blazingpc.com/forum/showthread.php/8800gt_bios_volt_mod_guide-11441/index.html

RSSCM.rom available here... post 338

http://www.xtremesystems.org/forums/showthread.php?t=164242&page=14