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CPU Waterblock

Alphacool has included an XP3 Light CPU block here, and we have actually taken a look at this separately before here. That was the metal top version, and this is the Black (not Acetal as mentioned in the specs) top version but that aside it is identical in all other aspects.

As you open the box, which I did hoping the contents inside were in good shape, you see the accessories on the right and two documents on the left on top of the block itself. One warns you to not use tools to tighten down fittings on the block while the other serves as a small instruction manual/installation guide in multiple languages. This particular pamphlet is quite lacking in my opinion as the information included would really benefit from details and pictures. It also has no mention of LGA 2011(-3) support despite the block supporting it out of the box. Thankfully, there is an updated guide available online (and presumably in newer batches of the CPU block) that provides a lot more information.

We now get our first glimpse of the block itself, but let’s look at the provided accessories first. There are two ziplock bags there and the first one contains the mounting hardware as well as a tube of TIM. Along with the thermal paste are 4 Intel socket LGA 775/1366/115x mounting posts, Intel socket LGA 2011(-3) and AMD sockets mounting posts, 4 bolts, 4 locking nuts, 8 plastic washers, 4 metal washers, 4 metal springs and an Allen key to aid in securing the first set of 4 mounting posts.

Inside the second bag is a backplate for the various Intel sockets (but with a caveat- the backplate doesn’t seem to fit the LGA 115x sockets), a spacer and a mounting bracket each for Intel and AMD sockets. We will get to these in the installation section as appropriate.

On to the block itself now:

Some terrific packaging here- the block is covered in a plastic wrap first and then wrapped on all sides by thick soft foam. Even on the top, the foam extends up so anything hitting the box from top hits it and not the block. Great job here, and this is also why the block arrived in perfect shape despite the shipping and handling issues. The block doesn’t come with a mounting bracket pre-installed and is such more petite in dimensions and mass compared to the average CPU block. The black top in this case has a glossy finish on the top, which is unfortunate as it ends up being a dust and fingerprint magnet and wiping with micro-fiber cloth doesn’t help much either. On the underside we see the copper cold plate here with a warning label on it which also serves as a protective layer keeping it clean.

The cold plate is polished slightly but not a mirror polished as seen in the picture above. This is not going to hurt performance by itself as long as it does not affect TIM spread.

The ports on the front are too close to each other to fit large compression fittings such as the popular 1/2″ x 3/4″ Bitspower ones. On the other hand, hardline tube fittings such as the Alphacool 13/10 mm hardline fittings shown above, are not an issue. The 13/10 mm soft tube fittings included with the kit will be just fine as well.

As far as block disassembly goes (done after all testing was completed), there are just 4 screws holding it together on the back:

I like that the screws have a copper finish to them throughout, matching the cold plate. Once removed the block comes apart easily:

There is no jetplate here but the block has cutouts below the inlet port that aim to spread the coolant flow over the cold plate. The cold plate itself has two sets of 19 channels cut perpendicular to each other thus giving a cross pin matrix at the middle similar to some other blocks such as the Swiftech Apogee XL. On one hand, this means that block orientation is not a factor anymore on performance but on the other this didn’t bode very well for the Apogee XL compared to newer blocks using microchannels. The cold plate here is 56 mm x 56 mm in area, with the pins in the middle being 0.5 x 0.5 mm wide each and having a height of ~2.5 mm from the bottom of the cold plate.

Liquid flow restriction

Testing methodology

I used a Swiftech MCP50X pump with a FrozenQ 400mL cylindrical reservoir. The pump was powered by a direct SATA connection to an EVGA 1300G2 PSU, and was controlled by an Aquacomputer Aquaero 6 XT. There was an in-line flow meter previously calibrated, as well as a Dwyer 490 Series 1 wet-wet manometer to measure the pressure drop of the component under test. Every component was connected by 1/2″ x 3/4″ tubing, compression fittings and 2 T-fittings with the manometer.

t’s at the point where that plot is cluttered with data. So here’s another which might be more helpful:

In case you can’t view the interactive image properly, here’s a direct link comparing the tested CPU waterblocks available for retail purchase: Pressure drop of CPU waterblocks at 1 GPM flow

Most of the blocks are very close to each other, and the XP Light is no exception. But it is one of the more restrictive blocks here, owing to the cross pin matrix in the cold plate. We see that the only other block here employing a similar design is the more restrictive, with the XP3  Light coming in third overall. There’s a reason most currently designed waterblocks employ microchannels and that is to get a good amount of thermal surface area of contact while keeping fluid flow as high as possible. There may be a small increase in restriction with nickel plated cold plates wherein the plating thickness results in an even smaller channel of flow for the coolant. Since CPU blocks tend to be one of the most restrictive elements in a loop, accounting for a high restriction CPU block is a wise move when choosing the pump(s).

Thermal Performance

The tests were done on 2 CPUs across 2 different Intel Haswell platforms:

1) LGA 1150: Intel i7 4770k

This 4 core, 8 thread unlocked CPU is a mainstream CPU from Intel. The newer i7 4790k is based off the same platform and performs the same clock to clock, while perhaps running a bit cooler. If anything, the older 4770k would benefit more from a custom loop. Sorry, no Skylake hardware here!

Motherboard: Asus ROG Maximus VI Formula
RAM: Corsair Dominator Platinum DDR3 1866 MHz (2x8gb)
CPU frequency: 4.7 GHz at 1.4 Vcore

2) LGA 2011-3: Intel i7 5960x

The behemoth 8 core, 16 thread unlocked CPU has a very high heat load due to 8 unlocked cores. It is one that benefits from a custom loop for sure.

Motherboard: Asus ROG Rampage V Extreme
RAM: Corsair Dominator Platinum DDR4 2666 MHz (4x4gb)
CPU frequency: 4.4 GHz at 1.3 Vcore

Testing methodology

Pump: Swiftech mcp35x2 set to 1.2 GPM
Controller: Aquacomputer Aquaero 6 XT
Radiator: HardwareLabs Black Ice Nemesis 480GTX with Noiseblocker NB-eLoop B12-3 fans at full speed
TIM: Gelid GC-Extreme

Everything required was placed inside the hotbox and the ambient temperature set to 25 ºC. TIM cure time was taken into consideration and 5 separate mounts/runs were done. For each run, a 90 minute Intel XTU stability test was performed. XTU is a stability test from HWBot that uses a custom preset of Prime 95 to ensure the load is uniform on each run. CPU core temperatures were measured using Aida64 and average core temperature was recorded at the end of each run. Loop temperatures were recorded using 2 inline and 1 stop plug type temperature sensor connected to the AQ6 and the average loop temperature was recorded at the end of each run. A delta T of CPU core and loop temperature was thus calculated for each run with an average delta T then obtained across all 5 runs. This way the cooling solution is taken out of the picture. The measurement cycle was done for both blocks in both orientations and the average is reported below with standard deviation accounted for.

A reminder here that the orientation of this block does not affect performance, and hence there won’t be separate “regular” or “goofy” entries here. Now on to the results:

Note: If you are viewing this on a mobile/tablet and the interactive charts do not show up properly then please check here- 4770k, 5960x

Now I must say that all the blocks don’t scale equally with flow rate. So keep that in mind since these results are at a set flow rate. Note also that each review result can only be taken to fit that particular CPU being tested out and your results may well vary- especially with non soldered IHS on CPUs. With that being said, we see a few things that follow in line with what we have seen before. Alphacool notes that the black top version is ~ 2 ºC worse off on average compared to the brass top, but provides no information on what the testing conditions were when this was recorded. As such, in these particular testing conditions at least, we see that the XP3 Light Black is ~0.2-0.4 ºC worse than the XP3 Light Brass which itself was not the best performer to begin with. We see that the older design is found wanting here, with a lot of the newer blocks outperforming it. It also shows that the difference is not a whole lot, and some of it can be attributed to error margins of recording also. While I could say that this may be due to the internal heat transfer between CPU die and IHS being a bottleneck, the fact of the matter is that this 4770k is one of the better samples I have used in terms of internal heat transfer and the 5960x has a soldered IHS too. Sure, there is still some effect due to die-IHS heat transfer but not a lot of general progress has been made in CPU waterblock technology (or coolers downright for that matter) in the last 5+ years. This helps keep the Alphacool XP Light still relevant here, but it should not be treated as an excuse either.

So overall, the CPU block is a bottleneck to both flow and thermal performance alike, and may hold the rest of the kit back. The sooner Alphacool makes a new block, the better it will be.


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