hereiam

Please pardon the dust It's two CPUs in a row, literally, so I made a cardboard air duct. Had a lot of grief trying to make a low noise rack full of 4Us, so this was my solution. Cheap, ugly, but it works.

Strangely enough, one of my cheap mod involves a cardboard box warping around a NH-D9L to make a makeshift "air duct". Essentially to force air to go through the fins instead of side way. Somehow this managed to increase cooling performance without making the thing significantly noisier. It looks ugly as hell, but it is in a 4U enclosure anyway so meh.

Now I'm confused. On Thermalright's website it said that the Macho Rev. A comes with the TY-147 A PWM, a 140mm diameter fan with mounting holes similar to a normal 120 mm fan. The only actual 120mm diameter fan in Thermalright's fan catalogue is the TY-127 with a peak airflow of 94,8 m³/h. If there's a Macho sink with similar performance at 78.5 m³/h, I am seriously interested.

Sorry, I forgot to mention that I used the 140mm variant of the SR2 fan to have a more apple to apple comparison, since I could not find the exact 120mm variant of the Macho fan. For some weird reason, Thermalright has three 140mm fan variants (TY-147A, TY-147B, and TY-147ASQ), but only one 120mm fan variant (the TY-127), making apple to apple comparison quite difficult. You're right though, don't just plug a 140mm fan into a heatsink made for a 120mm fan, most of the extra airflow would not actually flow through the heatsink and ended up getting wasted.

That's because the Shadow Rock 2 is of the very low noise (and low airflow) variant. The 140mm variant of the Pure Wings 2 fan has an airflow rate at max 104 m3/h, whereas the Grand Macho's 140mm fan has an airflow rate 125 m³/h top, about 20% increase. 20% increase in airflow is a huge deal. Not equivalent to a 20% increases in thermal sink rate, due to the aforementioned diminishing return, but still quite significant. The Noctua 140mm fan has an airflow rate of 140m³/h top, so you might want to use that if you want even better cooling performance. The Fuma has the Slip Stream 120mm fan, which has a 134.20 m³/h airflow rate, higher than even the 140mm variant of the Grand Macho, and is 50% more than the 87 m³/h of the Shadow Rock 2 120mm Pure Wings 2 fan. That's an incredibly large airflow for a 120mmx25mm fan. Plus the cooler has two of them, increasing noise even further. As a rule of thumb, for most fans higher airflow equals louder noise. That's why BeQuiet! usually uses low airflow and low noise fans, and performance suffers as a result. As a side note, it is incredibly hard to have apple to apple comparison between coolers. There are so many variations to consider: fan airflow, pwm-airflow curve, (as previously mentioned) contact thermal resistance, etcetera. Even the geometry of the inside of your case can affect (theoretically) the cooling performance.

From an engineer's perspective, everything is defined in equation 1, 2 and 3 in this article: https://en.wikipedia.org/wiki/Heat_sink So basically, in the case of a CPU, Q(dot) is the total dissipation rate, which is equal to the (thermal) power of your CPU. cp is the thermal capacity of air, which depends on various factors you have little control over (inlet temperature, humidity). m(dot) is the flow rate of your fan, which should be proportional (roughly) to its RPM and fan diameter. Rhs is the total thermal resistance of your setup, which is equal to (die to heat spreader resistance) + (thermal paste resistance) + (heatsink package resistance) . So how does all this determine the heat dissipation performance? If you fix the air flow rate, CPU temperature (Ths) and air inlet Tair,in temperature, the only variables you can control to maximize the total dissipation rate are 1) lowering thermal resistance Rhs, which involves bigger heat pipe, better thermal conductive material, better thermal paste or deliding; or 2) increasing outlet temperature Tair,out. The later is achieved either through bigger fins, more fins, increasing total surface area of the fins, or optimizing airflow to maximize heat exchange. As you might expect, all those optimizations have diminishing return, so the best heatsink will try to achieve all those optimizations simultaneously. TL;DR: there's no single most important factor deciding the performance of a heatsink. There's no point using huge heatpipes on heatsink with insufficient fins area. Similarly, huge heat sink with insufficient heat pipes to carry the heat to the fins is also pointless (unless you want to intimidate spectators).