While I am not going to go into detailed testing here specific to the 35X2, I will discuss my subjective thoughts and include the previous work on the 35X pump that can be used to consider noise. They are after all the same exact pump motor and very similar in pump top style, the only difference is we have two pumps that can produce basically twice the pressure as the same RPM. First let’s take a look at the 35X results from my pump noise testing round 1.
If the 35x (Single Pump) is decoupled from direct metal contact, it holds a noise level very nice and low a majority of the operating RPM range up to about 2.3GPM in that previous test. It isn’t until you push those peak RPM levels when noise starts to pick up and a more noticeable whine develops. This is where running two pumps does have a slight noise advantage over a single pump. It essentially produces the same amount of pressure at half the RPM level so you can operate at lower RPMs and still have gobs of power. Subjectively I would rather operate the 35X2 at 40-50%%PWM over a single 35X at 100%. The lower RPM is superior in both noise and heat.
Then there is the “HOW YOU USE IT” question. If you take advantage of PWM and throttle the pump speed according to temperature needs, you can get the best of both worlds of low noise and monster pumping power performance when you need it. In my long-term 35X use I found this to work extremely well. When surfing the net and doing office related tasks, I had speedfan dialing the pump down to 30% or so levels which is how it operates most of the time in complete silence. Then when gaming, I typically use headphones or when bench-marking I don’t mind a little extra noise, that is the only time the pump cranked up the power automatically to gain maximum performance at the expense of some noise. When wearing headphones I can’t hear the increased pump speed regardless, so it was an excellent and smart way to run the pump.
Pump heat of the DDC series pumps can be high producing a base that is hot to the touch and should be considered as part of the install depending on how the pump is used. If you utilize PWM to throttle the pump down in speed a majority of the time, the heat levels will likely be kept down to levels you can ignore. Pump heat is also significantly dependent on the restriction level of the system where the more restrictive (lower flow rate) the less heat. You can read about some of the DDC pump heat testing I’ve done here.
In addition an active or passive heatsink can also be an effective way to help not only keep the pump cooler, but also reduce the amount of heat added to the water/coolant. At the moment, the MCP35x-HS would not fit without modifying it, but a 35X2-HS (heatsink specific to this pump) is in the works and should be available toward the end of February or early March.
At a minimum I would suggest using only two of the neoprene pads on the outer edges such that you have about a 1/4″ of air space under the pump centers and place the pump in a location where air can blow under the two pumps.
Alternatively, another effective way to both decouple and cool the pumps is to allow the pump to be suspended by tubing. The best mount in terms of noise and heat is no mount at all..:)