The following summary plots waterblock cooling performance based on CPU Die Simulator against each waterblock's pressure drop. The Die Simulator is a pure performance test which excludes secondary heatpath effects found on motherboards.

Pressure Drop is an important consideration in waterblock purchases. If two waterblocks have equal C/Ws, the one with a lower pressure drop will not require as strong a pump (measured by head) compared to the other. Conversely, a waterblock with a superior C/W which shows a large pressure drop may require an expensive pump to attain performance at even one gpm.

Results are presented at one gpm because tests indicate that one gpm is an important "dividing point" for several reasons:

• Most moderate waterpumps (eg, 150-300 gph with 60" head) will deliver one gpm in a fully configured system (one waterblock, radiator with ½" tubing and fittings), with minimal restrictions
• Many waterblocks will show a performance gain of about 1-2 C up to 2-3 gpm
• Many waterblocks will show a performance decrease of about 1-4 C substantially below one gpm

For most systems, considering waterpump cost, one gpm is within reach and a good cost/performance tradeoff. Waterpumps which can achieve higher flowrates are higher cost, much larger and add more heat to cooling fluid than a moderately powered waterpump.

The C/Ws in this summary indicate the difference, in degrees Centigrade, among the waterblocks tested. For example, at 100 watts, the difference between waterblock A and B is three degrees C; at 50 watts, 1 ½ C, and so on. Closely ranked waterblocks may, in fact, show little or no difference, or even reverse positions, when compared in a specific system and especially at heat loadings of 50 watts or less.

The best possible combination: Low C/W and low pressure.

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