I am having trouble getting 2 8800 gts 640 to run stable in sli. It will only run about 30 to 40 seconds in 3dmark06 or in a game (crysis). The only thing i can see that is bad is that the cards set so close together in the motherboard that one of the card is getting to hot. From no airflow. I can run each card solo and have no problems. Even with both cards in and sli disabled it still locks up after a short time. Nothing overclocked.

system is:
e6750 @2.66
Asus P5N-D mother board
4gb ddr800 supertalen ram Cheap stuff
650w Cheifmax Power supply <- dont give me crap it works
2x 320gb segate SATA drives
ide dvd burner

Thanks for the help.

Have you checked your temps at load?
You should have that PCI1X slot right below your first PCI16X slot, might be able to fit a slot cooler in there to exhaust some heat from the case.
I know the power supply works, but the only 650w power supplies recommended for the 8800 GTS 640 are Tier 2 and above. Still could be a power issue.

Is crysis sli friendly. Thought I read it wasn't.

Gotta be a heat related issue. Pop the side off and blow a fan on it if possible and see what happens.

My 8800 gets way hot too. Major disappointment in nvidia. Swapping to an antec 900 helped solve the problem. Lots of airflow.

I forgot to put the temps in my 1st post. card 1 core was about 75C. Card 2 was about 63C. at load. I also tried a big box fan to blow in the side of the case and that did not keep it from crashing. The 2 cards are only about 1/16 of an inch apart. How are you supposed to get airflow.

As far as crysis , it worked ok for a min or two. I had hoped to play at 1680 x 1050 at very high.

No big deal I guess, If i dont get it to work my wife will be more than happy to get a 8800 for here machine.

If the temps are showing accurately that seems pretty normal for full load.

The power draw for a single 8800 gts 640 is 105 watts at full load, so you're talking 210 watts sustained for 3D.

I don't think your power supply is up to the task, for one I found it on pricewatch for $25.00. The same model tested by jonnyguru died at a peak output of 184 watts: http://www.jonnyguru.com/modules.p [...] nt&reid=71

yeah the power supply was cheap.
ok thank you for the info. I will get a SLI approved power supply and try it. I just did not want to spend a fortune on it.

Totally worth it, I had problems with my SINGLE 8800 640 after about two months with my cheapo power supply and my Antec 650 fixed the problem. I used to try and cut corners by saving cash on MOBOs and PSUs but it's just not worth it.

It's your PSU dude. Get yourself a good 750+ PSU with decent Amp ratings on the 12V rails..

Cheap parts are just asking for trouble. You can get cheaper parts, just don't cheap parts. You can only get so cheap before you sacrific quality and stability. An overloaded PSU or cheap one can actually blow out components. You don't want that.

http://www.newegg.com/product/prod [...] 6817341002
Will this one be ok for my system. I did not realize what a POS my cheifmax was. Learn someting every day.

Good find, order it! SLI Certified and good price. Also, for future SLI reference, try NVidia's SLI PSU site: http://www.slizone.com/object/slizone_build_psu.html

I would think it would be fine. If you are planning on doing any OCing you might want to get something with a little more juice. if you are all stock it should be fine. Looks like a great deal.