Overclocking Water-cooled GPU's

[tarrant_01]

I have 2 Visiontek 7970's being watercooled.  I'd like to overclock them to 1200Mhz range as seen on the hardware comparison chart.  Everytime I try to go that high it just locks the computer up.

I'm wondering if I need to increase the voltage to achieve that range.

Current settings:
Engine: 1125 Mhz (About 670 Mhash/s at this speed)
Memory: 975 Mhz
Vddc: 1.170 V (stock)
Powertune: 10%

Temps are currently 54C.

They are on a 1000 watt PSU.

[tarrant_01]

Any tips on what I should do?

[grue]

Keep in mind you're supposed to underclock memory unless you're mining scrypt (which I don't recommend). As for voltage, the general rule is that you increase voltage until it's stable OR it's too hot (over 80 C). Since every chip is different, it's impossible to say how much voltage is needed.

[tarrant_01]

Right. The memory is currently underclocked. The stock is 1375 I believe. I haven't used afterburner yet, but cgminer only allows me to keep it within 150Mhz below the engine speed.  I've never messed with voltage before.  Any suggestions on the amounts I should increase it by?

[Marduk]

Right. The memory is currently underclocked. The stock is 1375 I believe. I haven't used afterburner yet, but cgminer only allows me to keep it within 150Mhz below the engine speed.  I've never messed with voltage before.  Any suggestions on the amounts I should increase it by?

You always want to increase voltage in the lowest increments possible to keep it stable.  Your cards might even be voltage locked.  I'm not sure which ones are and aren't.  

Be careful messing with the voltage though.  Chances are that you wouldn't fry it with afterburner default ranges, but as was said, keep an eye on your temperatures.

Also, with the newer AMD drivers, they force you to keep your memory speed within 150Mhz of the core clock.  There's no way around this except by using older AMD drivers, and an old version of Afterburner.  There's some threads out there about this.

I'll refer you to eocf.com (forums.extremeoverclocking.com) to read more about overclocking.  Read through the stickies there.  That's where I learned to overclock my computers 10 years ago.  

hardforum.com is another good overclocking forum.