We did a few rough sketches about a month back (If I had my scale I could have done much better). I'll see if I can get them from him and double check the measurements, but I'm pretty sure It will fit in a 4U. The main thing in the way is the heatsink for the cpu. We didn't have a sempron since we used two motherboards we already had, but we estimated with another stock heatsink and it fit. If this is a problem, you can find a cheap low-profile sink on newegg. Other than that, the cards only need to be just taller than the peripheral outputs on the back of the motherboard.
For two power supplies, just put one on the left and one on the right in the back of the case. We didn't really look into dual power supplies because the card we use (can afford) was the 5830 and each one uses about 200W each (OC'd) so we would buy a 1000W PSU for 4 of these or a ~1500W for 6. We looked into a motherboard that could support 6 cards, but this was a substantial price jump, $170 vs $80. so we just panned on doing 4 cards in a case. Gives them plenty of room to breathe anyway. If you were to use more than 3 dual gpu card, 5970 or 6990, then you would be forced to use two PSU's. At that point you would need a separate breaker for each 1500W PSU!
I'll have more details when I get the old plans. PM me if you want to talk more/let me help/have me consult. I'd love to since we never got to build it ourselves
For two power supplies, just put one on the left and one on the right in the back of the case. We didn't really look into dual power supplies because the card we use (can afford) was the 5830 and each one uses about 200W each (OC'd) so we would buy a 1000W PSU for 4 of these or a ~1500W for 6. We looked into a motherboard that could support 6 cards, but this was a substantial price jump, $170 vs $80. so we just panned on doing 4 cards in a case. Gives them plenty of room to breathe anyway. If you were to use more than 3 dual gpu card, 5970 or 6990, then you would be forced to use two PSU's. At that point you would need a separate breaker for each 1500W PSU!
I'll have more details when I get the old plans. PM me if you want to talk more/let me help/have me consult. I'd love to since we never got to build it ourselves
This is why I was thinking of doing a 5U case. That will allow me to raise the cards a bit off from the mobo and space them apart so intake fans don't get blocked. Then all the cards can just be hooked up with ribbon risers.
Anyway, looking at all these other designs has given me a lot of ideas to test out and luckily I've got a lot of time this weekend to get some more work done on designing.