macdan modding a single cpu heatsink for a dual Quicksilver cpu I replaced the single cpu in my 1st generation Quicksilver (733 overclocked to 800) with a dual 800mHz cpu. However my new dually cpu was purchased naked without a proper dually heatsink. The single cpu heatsink won't work with the dual cpu, the contact area isn't large enough to cover the dual cpus. Having had no luck sourcing a proper dual cpu sink (and being too impatient to look any more!) I decided to rework my single cpu sink. I needed to enlarge the contact area to accomodate the dual cpus, so I decided to cut out the center of the heatsink's contact area and replace it with a larger but same-thickness block of copper. As part of my design brief I wanted to be able to use the sink with either single or dual cpus. I'm unsure why Apple decided to use two different sinks, it appears to me it would have made some sense to have just used the dual sink with all cpu versions,

Sourcing the copper wasn't as simple as I had expected. Locally none of the metal suppliers had anything suitable, unless I wanted to purchase large quantities. I ended up at a scrap dealer, who helpfully dug through his copper scrap barrels and came up with a lovely 12 lbs. brick of solid copper. Conveniently, the cross section was almost precisely the dimension I needed. I never knew copper could be so tedious to cut. I labored with a hacksaw for quite a while, but eventually hauled out my circular saw with a metal cutting abrasive blade and crudely chopped off the chunk you see above. I hated to waste all the copper that got ground up in the cut's kerf, but I was fed up and my arm was sore. Next I had to thickness and flatten the raw chunk. Yeesh! I started out using my funky machining center (a-two-axis-manually-operated-cross-feed-table-and-endmill-in-my-drillpress-thingy), but that was taking forever. I eventually ended up just grinding it flat on my big 36" belt sander. By going very slowly and carefully measuring often I was able to get it quite flat and the precise thickness required. I finished it by wet sanding both sides on a piece of wet-n-dry paper laid out on the cast iron deck of my table saw. Next step was to cut out the center of the old heatsink. It took me some time to devise a way to do it with my above-mentioned machining center, but eventually I did get it set up in a way that was at least functional. The pic below shows it after I had finished smoothing the contact area with fine wet-n-dry paper, using the now-flatted copper chunk as the sanding block.

And finally, here's a couple of pics of the final result.

The copper block is mechanically attached with only the one screw. The block is quite flat and mates perfectly with the sink's surface over its entire length. There remains very tiny gaps on each side and I haven't yet figured out exactly how to fill those, nor if I even need to bother. I liberally smeared silver-bearing heatsink paste between the sink and the copper. I used dabs of the same between the cpus and the copper. I'm quite satisfied the copper effectively transfers heat to the sink, under hard use the sink rapidly gets quite warm, just as it should. However, I'd like to see the sink temp come down a bit, especially as I intend to overclock the cpu. To that end I've been researching and thinking over my options. My first inclination was to assist the original cpu fan increase the airflow through the sink's fins. To that end, I added shrouding around the fan and also to the sink itself. Now the cpu fan pulls much more air directly through the entire central fin area. I shrouded the fan's output to direct more to the exhaust area, without which much of the fan's output is dumped back into the case. I also added a second smaller fan just above the main fan, see the pic below. It just dumps its output back into the case but it does seem to help keep the sink cooler. You can see the shrouding in this pic. Using aluminum foil tape I covered the sides of the heatsink to ensure all forced air passes through the entire heatsink.

I'll have to get a cpu thermometer so I can confirm the results of any mods, as well as keeping an eye on overall temps. Other cooling options? It's quite possible to add a separate external cool air intake exclusively for cpu cooling. That would involve running a duct from an intake in the top or lefthand side. The intake would be invisible from the outside, hidden beneath the polycarb cladding, similarly to the exhaust of the large fan located below the power supply. Watercooling? Well, I've got this here block of copper and the thought does occur that it wouldn't be difficult to use a couple of chunks to fabricate some sort of watercooled arrangement. It's really a plumbing problem, something I'm quite comfortable tackling. Lots of room for a heat exchanger in the space above the optical drive. Hmmmm . . . Worth the bother? Depends. I'm pleased though. :-) My original cpu lacks an L3 cache, and since the dually has 2MB L3s that alone makes a significant difference. My initial Q3A(G4) tests showed an immediate boost to the timedemo framerates (res=1280x, everything maxed), from ~62fps single cpu went to ~74fps with the dual. I'm still cpu-limited, my GF4 Ti isn't even close to being overtaxed. Of course, since X uses dual cpus for lots of stuff, I expect an overall boost in . . . lots of stuff. :-) Also, I intend to overclock from the current 800. I hope to get to at least 933, and won't be surprised if it'll do over 1gHz based on all the reports I've read. All in all, not a bad upgrade for a couple hundred bucks and a couple of hours in my workshop. back to macdan revhist 2005.01.04 - added fans pic 2004.12.23 - new page