SLI Temperature difference

[Lankoss]

I know it is normal too see the top card hotter than the lower, but at what differential would be considered abnormal? I have 2x GTX 780 Lightning's running in SLI. The fans on them are pretty quiet so I have them running at 75% once they get over 60 degrees. I have just benchmarked them and the bottom card maxed out at 53C and the top 73C, so a 20C differential which is more than I was expecting. Is this high spread due to them not being reference models? They are only around 1 inch apart as well and the bottom one is blowing hot air directly into the top ones fans so I think all of this is compounding and making the top card significantly hotter. Let me know your thoughts.

 

[Lankoss]

I get a 10% difference at idle on the desktop increasing to around 15-20% in games.

You're seeing around a 40% difference, so quite big, but I'm using a Corsair 450D case, one of the very best cases for air flow there is, with 3x120(pulling out warm air) and 2x140 (pulling air in) fans keeping things cool, also 970's do run cooler than 780's.

As long as they stay within the safe thermal parameters I wouldn't worry about it too much.

I have the fractal design define S, there's literally nothing between the fans and the GPU's as there is no HDD trays. I have 3 140MM fans blowing air from the front and 2x 140mm pulling the exhaust air out (one ontop at the rear and one rear fan). All fans are running at 1400rpm as they are very quiet.

All i can put it down too is the coolers on them and the fact that the 780's generate a fair bit of heat, i can't see anything i can do to improve temps short of buying an ATX board and spacing the GPU's out further which im not going to do for obvious reasons

 

[Lankoss]

Do the intake fans on the front of the case blow cool air onto both or just the lower card?

Yes, i have 3 fans on the front in the top, middle and bottom position so the whole case gets cold air.

 

[Lankoss]

Thanks for the replies guys, the temp of my top card is still only 73C (during benchmarking) so I don't think there is anything to worry about, i will just have to live with it I guess. Hopefully temps won't hinder my in terms of overclocking as there isn't really anything I can do to improve temps short of watercooling which I'm not going to do.