Maximum PC

I've got two 9800 GX2 cards ready for quad sli. Most available waterblocks are pretty spendy - close to the value of the cards themselves. If I crank the stock HSF(s) to 100% I get these results:
Both chips of a single card run at 54 C.
With a second card installed, the two chips farthest from eachother run at 64 C, while the two closest to eachother run at 74 C

I'm looking for any building or modding advice using either existing HSF or from parts I can buy. I'd like to try this before shelling out the bucks for a peltier or other type solution.

Have you tried replacing the thermal paste with a good one like ICD7?

No, but thanks for the recommendatio. I just opened the case on one to check out the HSF. It uses a thermal gauze-tape with white paste on the ram and some grey/silver paste on the GPU. Could probably do with an upgrade.
In the end I probably won't stop until I've cut cards apart and made them my own, but it will be interesting to see how much of a difference a good thermal paste can make.

Be VERY careful doing this. That gauze tape looking stuff is more important than you might realize. It also fills in the little spaces between the PCB and the cooler. Gaps that cannot be filled in with regular thermal pastes. Just removing it and putting thermal paste on there is NOT a good idea because the thermal paste will not fill in the gap like that gauze stuff does and you could end up burning up the memory, rendering the cards useless.

Places like Petra's Tech Shop sells a much better thermal tape for the memory modules. So either leave that white, gauze looking stuff on the memory or, buy some after market memory tape specifically for watercooling.

Not sure what happened, I think I took too long writing a response and did the back button-cut and paste thing wrong.

Anyway, thanks for the heads up quakindude, I couldn't find any thermal tape at petras so I'll either have to reuse the existing or find another source.

Maybe it was FrozenCPU I was thinking about. Last time I ordered, I got enough for three video cards and only ended up using one set. Personally, I used this stuff since the pads for the MOSFET's heatsink are the same as what I've seen on most video cards as well.

I'm pretty sure it was FrozenCPU I got it from, but that's been a couple of years ago and my memory sucks. Look around and see if you see something that might be closer to your application. I've got an 8800GTS 640 still Folding for Elena on our Folding team that has those very same pads I linked to on the memory chips. And that's been at least two years ago I replaced it.

Ack....as a matter of fact, I had to RMA that card not too long ago now that I think of it. But it was a case of the DVI connector going bad, not the memory. I could jiggle the DVI Plug and get intermittent display output. I was a bit sad that I got another 8800GTS 640 in return. Most people have been getting newer, nicer cards.

I found the tape at frozen cpu like you said Quakin'. You know, the hardest thing has been finding the right water blocks. They can't be more than 1/2 an inch thick, since I'm trying to slam two of them into the existing HSF. The Thermaltake aquabrazing generic GPU jobs should work but all of a sudden they're like on galactic backorder. There are some lower grade old-a$$ ones from Koolance but they have plastic tops and don't look like the water spends much time in the block. I've tried finding prefab base plates to make my own, nobody's dealin'.
Any sort of obscure, little known specialty shop anyone knows of would be a nice lead. Matt

anyone with a cnc machine could make a water block you would just need a design. The most important thing is lots of contact area the water should move through fairly quickly to keep cool water coming in.

Have you checked Danger Den's site? Also you might try looking at EK Water Blocks and SwiftTec?

Checked all of them already. Dangerden has a GX2 cooler for around $200, Ek has one for $190, Swiftech doesn't make a perfect match and their universal is too tall. Nope, if I could get my hands on four Thermaltakes I'd be set. Short of that I do know a few machinists so maybe Danthraxx has the right idea.