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780 Price Cut...Is 360mm Rad Enough for SLI 780s?

gun5l1ng3r

Member
May 20, 2013
29
0
0
Hello All!

With the 780 price cut looming...

I have been running this idea through my head for awhile...I Currently have a H100i on my i7 920 and it runs quite cool. I am considering getting a a second 780 SC ACX and dont know if I should switch my 920 back to air cooling with a NH-D14 and water cool the SLI 780's w/ a custom 360mm water loop, or keep the H100i on the 920 and cool the 780's with air only (I am going to run the 780's in PCIE 8x and have them separated by a few inches)...I have 4x 200mm fans and 1x 140mm fan in the HAF X.

I only plan to OC the 780's to about ~1150mhz on core and hopefully about 6300mhz on ram...so the TDP should stay close to stock...

I know some people have modded the HAF X to accept a 240mm and 360mm rads, but that means getting rid of my HDD cage...

I dont have the second 780 yet...but I have been thinking about this for awhile and the forum seemed like the place to get some input...Do you think a custom 360mm water loop can cool 2x 780's at ~1150mhz core?

I understand the cost difference and am willing to accept it. This would be my first custom water cooling loop. I have been wanting to get into it for a while and have liked the results of the AIO of the h100i....

I game at 2560*1440, ultra settings on a MicroCenter Auria IPS screen. It seems that one 780 isnt quite enough in some instances (BL2 w/ Physx turned up, Metro 2033, Batman: AC w/ Physx turned up; I have already tried a dedicated 650Ti for Physx and it didn't produce the results I was looking for) and I don't want this to turn into a thread questioning my reasons to go SLI...I have always wanted to have 2 video cards and right now I am able to attain such niceties....

My system:

Seasonic Platinum 1000w
i7 920 D0 @ 3.6ghz @1.152v
EVGA X58 SLI LE
Cool Master HAF X 4x 200mm fans, 1x 140mm fan
EVGA SC ACX 780 @ 1137mhz core 6840mhz vram
H100i cooling the 920
WD Blue 1TB
Corsair Force GT 120GB
WD Velociraptor 1TB
 

Grooveriding

Diamond Member
Dec 25, 2008
9,080
1,199
126
It is not ideal. I would say 480, but you can get by. Just will have higher temps than you could have. I am running overvolted 780s and a 3930k overclocked on 600mm of rad and it is not enough to get temps as close to ambient as they could be. I could stand to have another 240 of rad.

I think it will work though. You might see load temps mid 40s though, which is still great.
 

blackened23

Diamond Member
Jul 26, 2011
8,556
1
0
You can probably do 1100-1150 on the core without water cooling if you buy the right card. What I've found is that quite a few OC edition 780s boost to 1070-1100 out of the box, and some of them have a wee bit more headroom over that. If you get a classified or something along those lines, you can up the voltage to hit past 1150.

That said, I personally think you'd be okay with a 360mm rad. General rule of thumb is 120mm-240mm rad per item being cooled in the loop, so 480 like groove said would be preferable. 360 will work though. I wouldn't necessarily use a custom loop without a voltage unlocked card like the 780 classified, though - using water cooling on a plain jane 780 without OV capability won't help you as much as it would with a classy. That's the card you want for sure if you're going for water cooling.
 

BrightCandle

Diamond Member
Mar 15, 2007
4,763
0
76
What you intend to cool in your loop:
2x 780 TDP 250W, overclocked probably 300W - 600W total
1x overclocked i7 920 ~150W

Total cooling necessary 750W

Using 800rpm 120mm quiet fans on a thick radiator every 120mm of radiator space will cool around 130W to 10C water delta.

Given that you would need: 750 / 130 = 5.8 = 6 x 120mm radiator slots to cool the components.

What about if quiet isn't an option? Well then we can get more cooling per slot. A 2000rpm fan can increase the amount of cooling per slot to around 200W, all be it very noisily. At that speed its possible to cool your components to 10C (when they are all running at the maximum) on just a 4x 120mm worth of radiator.

I can propose something else however that does work. If instead of adding the CPU you just keep your loop to the 2x 780's and look at cooling just the 600W you can run a 360mm hot loop. That means instead of targeting 10C delta we target more like 20C, which isn't an acceptable temperature for a CPU but for a GPU it works fine. GPU hot loops can get away with being severely under cooled and the 10C extra temperature compared to a good cool water loop will still be fine. They don't perform as well but they do still outperform air at around 20C deltas. That should work on a 360mm radiator with 800-1200rpm fans at around 15-20C delta.
 

phillyboy

Member
Jun 3, 2006
26
0
0
My overclocked 3930k and overclocked crossfire 7970s drew about 600 - 650 watts at the wall, for what it's worth. So you are looking at in the 540 - 585 watt range for cooling as I have a platinum power supply. Unless those 780s draw significantly more then 7970s do (I thought they didn't, but I could be mistaken).

I cooled all of this on a 140.3 radiator (so 120.4) with Noctua NF-A14 fans set around mid-speed. Temps were in the 55 °C on the cards and 60 °C on the CPU. Water deltaT was around 20 °C so definitely higher then 10 °C but as you can see the temperatures were still great compared to air cooling those video cards :). Temps always seem to skyrocket for me when you have more than one card on air but maybe that is my experience (these were two MSI blower cards as well).

The general rule is 120mm of radiator per component + one extra 120mm, so if you are doing 120.3 for two video cards I would think that would be fine.

I now have a 120.4 and a 120.2 radiator cooling everything now which brought temps down a few °C (and I can run the fans slower).
 
Last edited:

gun5l1ng3r

Member
May 20, 2013
29
0
0
What you intend to cool in your loop:
2x 780 TDP 250W, overclocked probably 300W - 600W total
1x overclocked i7 920 ~150W

Total cooling necessary 750W

Using 800rpm 120mm quiet fans on a thick radiator every 120mm of radiator space will cool around 130W to 10C water delta.

Given that you would need: 750 / 130 = 5.8 = 6 x 120mm radiator slots to cool the components.

What about if quiet isn't an option? Well then we can get more cooling per slot. A 2000rpm fan can increase the amount of cooling per slot to around 200W, all be it very noisily. At that speed its possible to cool your components to 10C (when they are all running at the maximum) on just a 4x 120mm worth of radiator.

I can propose something else however that does work. If instead of adding the CPU you just keep your loop to the 2x 780's and look at cooling just the 600W you can run a 360mm hot loop. That means instead of targeting 10C delta we target more like 20C, which isn't an acceptable temperature for a CPU but for a GPU it works fine. GPU hot loops can get away with being severely under cooled and the 10C extra temperature compared to a good cool water loop will still be fine. They don't perform as well but they do still outperform air at around 20C deltas. That should work on a 360mm radiator with 800-1200rpm fans at around 15-20C delta.
I plan on cooling only the 780's with the 360mm...I dont think a 420 will fit in the top of a HAF X...
 

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