Fan dynamics...
I was thinking and I don't like doing that these days...
scenario
intake fan max RPM is 4500 rpm and is spinning at 3400 rpm
exhaust fans max rpm is 2400 rpm and is spinning at 2600 rpm
a> is the slower exhaust fan actually slowing down the intake fan as it is being forced to spin the exhaust one faster than it can electrically spin itself?
b> is the exhaust fan even electrically doing anything since its exceeding its max rpm due to the intake fans higher rpm
I am guessing the exhaust fan being that much slower isnt doing anything but causing impedance and should be removed. correct?
I can match it but don't like the extra noise but if its not actually doing anything then I dont need an exhaust fan anyway....
While I am not an "airflow engineer", here's another possibility:
c> The exhaust fan is lowering the pressure that the intake fan "sees", and hence the intake fan speed can be reduced without having the miner overheat.
Bingo.
It's all about static pressure. I haven't actually checked their specs but I'd wager that despite the exhaust fan spinning slower it is still rated with same CFM
when working against a light resistance as the intake fan is when the intake is working against high back pressure.
Difference is that that intake fan can move that air against the high resistance all those heatsink fins produce. The unloaded CFM of the intake fan is much higher. Put the 2 fans together and it's a win-win.
side note: The 1-fan s7 proves that the 'help' the exhaust provides is not necessarily needed. I have 3 of them running full stock speed in 85F ambient and they are perfectly happy.