I've already got a 40mm fan from an older Asrock case that I was contemplating adding to it but right now I'm playing more with the case itself. I've got a Define-S with 3 140mm fan intakes in front and 1 140mm exhaust fan in back and the area above the PCIe slots removed and the PCIe slot covers removed for exhaust. I just removed the top rear vent cover and was surprised that it was acting as an air intake. Opening up did nothing for the VRM temps though. I even put a 140mm FAN here to blow air on the VRM but all it did was slow the temperature climb and not stop it. The temps inevitably climbed to twice the CPU temperature.
I was really shocked at how the Linpack test drove up the VRM temp.
3725 CPU=43C, VRM=86C (default voltage)
3900 CPU=55C, VRM=110C
3925 CPU=57C, VRM=113C
3950 CPU=59C, VRM=118C
3975 CPU=62+, VRM=124+
So, to me this is the thermal wall that people are hitting at least on the B350 boards. The VRM's just are not designed for the voltage necessary to do 4.0Ghz on these CPU's unless the specs say differently -- I'm guessing that they're rated at a max of 125-150C. I have my doubts that a better heatsink/air flow combo will make any significant difference unless you could transfer the heat to a different location where it can be dealt with properly which normally means water cooling.
I was really shocked at how the Linpack test drove up the VRM temp.
3725 CPU=43C, VRM=86C (default voltage)
3900 CPU=55C, VRM=110C
3925 CPU=57C, VRM=113C
3950 CPU=59C, VRM=118C
3975 CPU=62+, VRM=124+
So, to me this is the thermal wall that people are hitting at least on the B350 boards. The VRM's just are not designed for the voltage necessary to do 4.0Ghz on these CPU's unless the specs say differently -- I'm guessing that they're rated at a max of 125-150C. I have my doubts that a better heatsink/air flow combo will make any significant difference unless you could transfer the heat to a different location where it can be dealt with properly which normally means water cooling.
You might want to consider putting some sinks/bigger sinks and a 40mm fan on your VRM's.
https://hardforum.com/threads/am4-b350-x370-vrm-table.1928342/#post-1042945506