Good information to share about overclocking on the Asus A8N SLI.
Extreme overclocking 2 6800 ultras in SLI mode is quite challenging due to
spacial and powering constraints. But I decided to take on the challenge in
order to hit the big numbers.
As I was overclocking on the Asus A8N SLI board, I had 58mm of space between
graphics card 1 and graphics card 2. Therefore, I had to devise a cooler to
fit in between this space factoring insulation, etc. Phase-change was the best
bet for me so I went onto building the phase-change cooler for the card.
As I was anxious to get the benches rolling, I decided to go single-stage for
one of the graphics card. The other GPU could be cooled by my existing GPU cascade
cooler. I rushed out the GPU cooler in 2 days using the evenings after work.
For the evaporator of the GPU cooler, I decided to go with the simple and effective
“cap-in-cap” design. I used a 6mm thick base with lots of copper caps
for surface area and routing of refrigerant flow. The way I make my evaporators
can be seen here.
The difference was that I made my evap exit at the side of the cap rather than
the top in order to save space:
The evaporator was mounted onto the insulated graphics card with some really
fine screws and an acrylic hold-down. I wish the nvidia cards come with bigger
holes for mounting.
Here you see it after further insulative touch-up. As marked in the picture,
it shows where I positioned the copper flexible hose:
The rest of the suction line is just 1/4″ copper pipe.
The condensing unit of the cooler is positioned at the bottom of my rack:
It consists of a 1 Horse Power Rotary Compressor which I run with R22 + a little
The bottom rack now has 4 compressors: 2 for my GPU cascade, 1 for my Northbridge
(which is unused with this board) and 1 for the additional graphics card.
Here you see GPU2 mounted on which runs off Cascade cooling:
And here you see the big picture: My benching wagon.
So under the load of the cards benching at 600Mhz /1300Mhz, GPU1 with R22 holds
-52C while GPU2 with R1150 holds -95C. Both cards are modified to run 1.67v
the same way as here.
For the Asus 6800 cards, I have not experienced any cold throttling.