Four 5850 cards Crossfire - heat distribution issues and low MH

[innerbitcoin]

I have four Sapphire Vapor-x 5850s, with all fans running at 100%

Ambient room temp is currently 18 degrees, but with summer approaching this could rise to 30 degrees or more as there is no aircon...

Card temps under load are:

card 1 (top) 92 degrees - av 250 Mh
card 2 (top) 76 degrees - av 330 Mh
card 1 (top) 84 degrees - av 330 Mh
card 1 (top) 59 degrees - av 330 Mh

I'd expect the top card to be hotter, plus it's powering a display (although mostly just VNC, and mostly not running the monitor, with windows set to disble screen output after 1 minute) . Is this why I am getting much lees output from the top one?

I don't understand why the 2nd one is cooler than the 3rd - any ideas? Maybe just due to airflow issues with some cabling in the way, proximity to airflow from case fans etc?

The bottom one with lots of clear space is obviously doing best.

All cards OC'd to 900 Mhz and fans on 100%

Anything else I can do to reduce temps, like downclocking the ram? I have not been able to work out how to do this yet...

Current plan is to try and ramp up the bottom one some more and maybe set the top one back to stock.

I'd love to be able to get a consistent 330 MH from the top card too... I'm thinking, maybe it's only when I am using a monitor or VNC to view this machine that the MH goes down?


Thanks

[BiggieJohn]

underclock the memory, and get more airflow to the cards. 
with 4 cards that close together, you might need to get pci bus extenders so you can move them further apart to get proper airflow.

[V2-V3]

place a spacer between the cards to slightly wedge them apart, than place a fan on top of the cards blowing down between them and this will greatly drop temperatures.

This is how I have my 3x 5870 and 1x 5970 running in my rig

[qed]

With 12°C more the top card will melt. Also running the fan at 100% is going to heavily decrease the life span.

I got some cables pci express 1x to 16x on ebay and are working great, cards will get way cooler.