Fan adaptor thoughts.

I was just thinking, yeah, I know that's dangerous....

If you have say a 60mm heatsink, and then get an 80mm fan with the exact same CFM as the 60mm fan, you are probably gonna get better temps, when you duct that down, because the ducting (good ducting that is, not one of those short *** ones that just obstructs half the durn thing) will eliminate the effect of the hub shielding the area above the core and give better flow there than with the 60mm right on top. Do you think?

Also I figure the ducting is going to reduce the churn, hot air being sucked back in the top.

So maybe if you've got good CFM out of your 60mm, just raising it some way off the sink with a duct or shroud would be as good as forking over the hard earned for an 80mm. It would allow space for the pressure to equalise and fill the gap behind the hub.

Anyhoo, maybe that was obvious, just seemed like a profound thought at this time of night

Road Warrior

One thing that will occur is the flow of air as it travels down the adaptor will decrease. Imagine the fan being a water pump and the water as the air. As you get farther away from the head of the pump, or in your case the fan, the flow of air will decrease, thereby reducing your CFM. I think that if you are going to use an adaptor, you should use a larger size adaptor and use a larger size fan to make up for the loss of flow from using an adapter.

I didn't think the frictional loss in like 2inch of smooth walled duct would really be significant.

rivercom9 is right I tested this out and your temps will be worse with the same cfm fan. You need to get a fan that has more cfms. The original fan blows right on the heatsink so will give better temps. If you can mount it closer to the heatsink then maybe the temps would be close but a higher cfm fan will be the best.

Hmmmm, maybe it's the turbulence factor, the duct lets the flow become too smooth.

Another thing to mention: the longer the duct, the more leverage is put onto the HSF. If it doesn't have a sturdy mounting, like a Alpha or something, the leverage could lift a corner of the HS off the core.

One thing I noticed when I used to use ducts was that pressure is just as important as CFM. Maybe the bigger fan with the same CFM will lose out because of this. Do you remember the Velocity Duct I was talking about a while back? I took your suggestion & cleaned the design up & I got less noise with the same performance.

Yes, I believe that pressure plays an important role in better cooling. Too low a pressure will result in less airflow and too much pressure MAY result in a smoothed out airflow which is not good for heat transfer, what we want is a turbulent but fast airflow. I havent yet tested this so this is just my thinking.

Spacing the fan above the fins or pins in you HS may do
little for your temps if you use the same fan, but you may
experience a good drop in noise.