Optimal Heatsink-to-Fan gap / LiteOn FS020 mod

[gbass01]

What is the optimal Heatsink-to-Fan gap? I am using a 92mm Panaflo L1A mounted on a Zalman bracket over an Alpha PAL 8942 (blowing onto the HS, no shroud, fan hub slightly offset from HS center). The original Zalman screw kept the fan quite a distance from the HS. I replaced it with a longer screw and a spacer to bring it closer to the HS, but I am still a fingerbreadth away from the HS. Should I move the fan closer still or duct the gap? With a duct the main issue will be turbulence, causing backpressure and noise as the exhaust cone hits the duct walls. Also, there's the hassle of designing and building a decent duct. On the other hand, the fan hub dead spot will be more of an issue the closer the fan is to the HS (or is it an issue already?). Any thoughts on the subject?

Ultimately, I am planning to duct from the front panel to the HS with the same fan mounted mid-duct, 5-6 inches from the intake filter. This should be the "coolest" LiteOn FS020 mod ever. Adding a 92mm fan to the intake side should help wiht the dreaded negative pressure issue.

Ducting note: 1/2 galon juice cartons are about 95x95 mm and of decent length. If I manage to figure out how to cut them to curve the duct down to the HS, I've got it made. Alternatively, I could figure out how to attach decent-diameter drier hose-type flexible ducting to a 92mm fan frame, I could make the curve out of that. BG Micro still lists a bunch of different fan sizes at $1 each, the frames (with the fan cut out) will make nice duct ends/connectors (I already have a couple). I can afford the BaDong, but even the "80mm" duct's diameter looks a little wimpy.

Boy, that turned out long.. WAKE UP!

gb