Review: Thermalright SP94, SP97 & other heavyweights

Cooling
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The weight of the SP94 and SP97 is essentially the same, at 590 and 585 grams without a fan. That's quite substantial, and a standard 80x25mm fan will typically add about 100 grams, and more if you opt for a larger 92mm fan, which these HS can accommodate. The net weight of ~700 grams is at least a couple hundred grams above either Intel or AMD guidelines for maximum heatsink weight, so care must be taken in transit. The bolt-through-board mounting method used for both models does go a long way to assuring high mechanical security, however.

Like the Swiftech and Alpha through-the-board mounting systems, these Thermalrights both use captive springs on machined screws to apply the correct amount of tension between the HS and CPU. The SP94 and SP97 use the same identical hardware, in fact. One set of this hardware is laid out between the two heatsinks in the photo below (no need for both sets of hardware; they are identical).


Clockwise around the heatsinks, from the to: 2 pairs of wire clips for fans, the installation guide sheet, bag of threaded inserts or anchors, washers, and spring loaded machine screws, CPU/HS support bracket for trace-size of motherboard (the anchors thread into this piece) and a tidy TIM dispenser -- enough for several applications.

The finish of the bases is excellent, but still a step below that of the Swiftechs, and half a step below the Zalmans. Fine ridges can be felt and heard with the fingernails. Fanatical readers may consider it worthwhile to lap (fine polish with sandpaper) these bases for improved smoothness, but IMO, the job of thermal interface material (TIM) is to help compensate for such imperfections. There's also evidence that a slight degree of roughness is preferable to perfect smoothness because the former provides greater contact surface area between the mating surfaces.


NOTE: The SP97 base on the left has the protective plastic sheet with which the unit is shipped. This plastic piece is secured by adhesive. Some of the adhesive remained in patches on one of the sample heatsinks after the plastic was removed. You must use pure alcohol and a cotton wad and some elbow grease to get rid of all the residue; if left, the adhesive could affect the thermal bond between HS and CPU (and probably goop it up badly).

The fins on the SP94/97 are shaped in such a way as to provide stepped notches that are perfect fits for 70mm, 80mm and 90mm fans. Two different wire clip sets are used in combination with three pairs of holes on the heatsink fins (visible in the photo above) to accommodate these difference size/thickness fans. This is the same clever design used in previous Thermalright thin-fin heatsinks.


The sturdy plain brown box favored by Thermalright haven't changed much, but it is a bit bigger for the SP94/97 than previous ones.


The packaging of all the bits and pieces is very nicely done as usual. The contents of these boxes would survive all but the worst handling in shipping transit.


The steel reinforcing plate has two sets of 4 holes so it can be used with either P4 or Socket-A. The plate has a square hard rubber pad in the center to insulate it from the motherboard PCB traces.

The Role of Heatpipes in the SP94/97

By now, just about every PC enthusiast on the planet must know at least something about heatpipes. Just to refresh your memory, here's a quick summary:

Inside a heatpipe is a liquid under low pressure (or vacuum) that boils into vapor when it absorbs heat. This vapor then condenses back into liquid at the cooler surfaces of the heatpipe and releases the heat. Heatpipes are capable of transferring a large amount of heat per a given volume of working fluid due to the phase change (liquid-to-gas-to-liquid-ad infinitum) that takes place. In layman's terms, it's vaguely like watercooling without the pump, but better. Here is a thorough, accessible explanation of heatpipes, by Thermacore.)

Normally, heatpipes are best used to move the heat away from the source to a point where it can be more easily cooled, either by forced air or by convection. A multi-finned radiator and a hot electronic component connected to each other by one or more heatpipes 6~12" long is fairly typical.

The concept in the SP94/97 is quite different: The three heatpipes are essentially being used to distribute the heat more evenly throughout the entire heatsink, especially the tips or ends of the fins. At first glance this just looks like a gimmick: Surely the thin copper fins are not long enough to benefit from the higher conduction of the heatpipes? The Heatlane Zen NCU-1000 CPU Cooler uses this type of heatpipe arrangement, but there, the distance between the base and the end of the tallest fin is 3 times that of the SP94/97. Well, the proof is in the cooling, so let's wait and see how the SP94/97 fares against the very similar SLK900, a known high performer.

Finally, there are better and worse mounting orientations for the heatpipes. A FAQ on the Thermalright website states:

Due to the multiple heatpipes we use on the design to minimize the gravitation effect on Heatpipe performance, we at Thermalright tested only 0.05 Celius/W on an open case environment for best/worst scenario with Panaflo FBA09A12H.

However, the illustration below from the instruction sheet ranks alignment from 1 to 4 stars. In any case, the best/worst difference may be larger with a low airflow fan, so adherence to this guide is strongly recommended.



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