Testing Restriction (Pressure Drop)
In a CPU only block type loop, restriction has little meaning as long as you can bleed out your loop. High or low restriction doesn’t necessarily relate to good or bad performance. Surprisingly you will see blocks with lower restriction also at times perform better than blocks of higher restriction. A lower restriction block simply means you’ll retain higher flow rates for other parts in your loop and may require less pumping power or be more compatible with more complex loops. In a multiple block loop, that means your GPU blocks and radiators will net slightly better performance because of the increased overall system flow rate, but that gain is always fairly small (couple of degrees). Blocks with really high restriction may also need a stronger or multiple pumps with multiple blocks loops sooner than blocks with lower restriction. It’s a balancing act of sorts, ultimately we would like to see high thermal performance at all flow rates and very low restriction…yet practically there is some give and take between the two.
I would simply suggest the following:
- CPU only loops with a strong pump – Ignore restriction, and base your performance purchasing decision on thermal performance only.
- Multiple block loops with a strong pump – Consider restriction. Average to low restriction blocks will help maintain reasonably good flow rates.
- Multiple block loops with a small pump – Strongly consider restriction. Low to very low restriction blocks may be required to maintain reasonable flow rates.
Continuing the same test method as before, I’m measuring restriction or pressure drop over the range of possible flow rates to get a complete look. First a picture of the pressure drop testing in progress. I simply increase flow across the block at .25 GPM increments and record the pressure drop across the block via the manometer.
Note that the meters I use are not calibrated and I believe my manometer may read high in general from absolute. With that said, the results should only be use for relative comparison only.
Now for the tabulated results detail and comparison to the Rev1 results:
The pressure drop has reduced from about 11.25 PSI at 1.5GPM to about 7.45 PSI or about a 30% improvement in pressure drop, that’s good!
Now for some relative context to the other blocks tested in this round. To help ensure relative accuracy (meter is not calibrated), I also retested the CPU-370 and EK Supreme V1 while I had my test bench up as a check. Results were similar to before, but I used the latest test for this comparison anyhow.
While the Rev2 pressure drop improvement is very good relative to the Rev1, it’s still a higher restriction block than the others tested as you can see above. It is a very welcome improvement, I just wouldn’t consider it a low restriction block. The Rev2 does however leave you more available pressure energy to push through a multiple block environment than Rev1. For example, the XT rev 2 drops about 3.5PSI of the MCP35X pump’s 6.2PSI produced at 1.0GPM. This leaves you with about 2.7PSI (44%) of remaining pump pressure at 1.0GPM to keep above that flow rate.
I would just advise against getting too worked up over flow rate, generally as long as you can bleed a system of air, the blocks of today will perform very well even clear down to the .5GPM range without much loss.
Bottom line, it’s a great improvement over Rev1, but still a higher than average restriction block relative to the other blocks tested so far.
