I build a PC for Folding, GTX 1070 + Silverstone 1200W platinum with stupid fan curve that can make you go crazy.
Before the mod- the PSU fan would Kick in at 100% for ~30 sec every ~10 min and after the mod it maybe kick in for ~5 sec once in 1~2 hours, even adding 2nd GTX 1070 its not kicking in so hard any more.
Also they maybe leave such big gap sometimes for economy reasons (using same blade on other frames?).
it's low RPM fan also it has almost 1 mm gap after mod for long term expansion, I tried 102mm ID and it also fits.
Case has 4 fans at stock placement, 3 at bottom sucking air in thru dense dust filter and 1 at back to exhaust the hot air[positive pressure inside case].
Fan Speed: 1200 rpm ± 10%
Bearing Type: Fluid Dynamic Bearing
Max. Airflow: 94.8 m³/h
Max. Air Pressure: 1.16 mm-H²0
Noise Level: 18.2 dBA
MTBF: Min. 50,000 Hours
Noctua-News: What’s the point of using such a small tip clearance? Is it really worth the extra effort?
Lars Strömbäck (Noctua CTO): *laughs* Well, it has taken us more than one year just to sort out the manufacturing issues, so there were times when we were wondering if it’s actually worth the extra effort, but at Noctua, we always strive to push the boundaries and deliver the best solution that’s technically possible. We’re confident that our customers appreciate this and that’s what’s justifying the effort for us in the end. Technically speaking, the reason why you want to go for such a tight tip clearance is that when the fan operates against back pressure, such as on a heatsink or radiator, some air will flow back through the gap between the blades and the frame. The smaller the gap, the less of this type of leak flow you have, so narrowing down the gap helps a great deal in achieving superior performance on heatsinks and radiators.
Look at the gap on Noctua: