On my cube v21, I have 2 side fans blowing at my gpu. Mobo is horizontal, with them on medium, around 1200rpm so they are relatively quiet, I get about 5-6c drop in temps... I think this is more about pushing the warm air away from the gpu than the cooling effect of the fan. With the top and sides off, the difference is around 2c.
The gpu temp at initial load takes longer to rise, which is noticeable since the fans take longer to turn on.
This is how my fans are installed, but I am planning to lower them closer to the motherboard tray, add a shroud of sorts to direct the air directly to the fans of the gpu, and add some exhaust above the gpu to direct the heat out of the case so it doesn't recirculate.
This will be how the shroud would look...
The gigabyte 1060 6g that I have runs almost 8c cooler in this case than it did in the CM HAF-XM case that I moved it from. I stay around 55c in the new case, but would run around 63c in the other case which had a side 200mm fan. I think that the 200mm side fan may have been pushing the warm air exhausting from the gpu back down onto it.
Ambient temps were cooler when I was using the older case, so the differential could even be higher.
In 2004 I did a bunch of experimenting...
Gutted a pci slot blower, added a fan adapter to it with an 80mm Tt smartfan... saw a noticeable increase in speeds compared to a side fan. Back then there were no temp sensors on the gpu. A 9800pro was used in this build.
Previously I had made pci slot fan adapters to blow air onto the front and back of the card, but it was not from an intake.
A few years later, similar pci bracket fans were sold mainstream.
My feeling is that if the bottom fan is blowing directly on the fans for the gpu, that it will be more effective than a side fan. The side fan should be lower than the gpu slightly to be effective as well. If higher, exhaust would be more beneficial than intake.
A bottom fan more forward than the gpu may direct the front intake airflow above the gpu, starving the gpu intake fan of the cooler intake air. Causing it to recirculate the warmer air in the case through the gpu increasing its temperature.
Each setup will be slightly different depending on case and gpu cooler layout. Longer triple fan coolers may benefit from a bottom fan in front of the psu while shorter ones will have a negative effect.Edited by EMUracing - 4/15/17 at 2:05am