Well I can answer this from VictoryShop experiences.
It is mostly about just how LONG you want to wait until the system is sucked/or blow up to good gas making hot enough.
BenP sells/supplies mostly to guys who will be stationary and “experimenters” with different fuel(s) inputs for different expected gasifier outputs.
Meaning flare-guys. NOT engine guys.
So 9"'s was the average lowest found that would satisfy the flare-guys.
Engine guys like ChrisKY, WayneK, and others do not even flare. Just get the gasifer going just enough to engine run and let a LARGE engine run some and then let the large engine VOLUME flows suck the gasifier into good producing.
I am now converted to the Mike LaRosa, Tom Collins, Dutch John way of using a good-and-plenty all metal carpet vacuum powered by a cheap Chinese inverter and just sucking the gasifier/and/system HARD and quick to performance.
Much less early cool gas crap system coating then.
BenP’s recommendation was for those why wanted a direct 12vdc blower with variable speed.
GregC the stronger sucking AMETEX made-in-America ones were nearly $400. USD.
Since you have two of the Chinese ones you can series run these if you want a higher static pressure.
WayneK and other do this with 6-5-6 very low pressure marine bilge blowers. Ha! Ha! Check their electrical watts needed and you can do more with less, man. (Doesn’t matter - they only blower run for mere minutes! Not flare staring hours.)
There are no to the third decimal point, importance’s in any real applicable wood gasification. Just broad overlapping spheres of numerical possibilities. It is not two dimensional chess - computer predictive. Not three dimensional chess - computer intuitive. Woodgassing has a fourth dimension needed. Human determination to make it work.
The difference between a by-the-numbers food manufacturer to the masses. And really, really good true scratch cook.
When numbers predictability can play billiards, soccer, tennis, baseball all of the human challenge will be gone.
This is why I have consistently refused to play the woodgasing numbers games.
But do insist on real make-power applications. That is real. And comparable to other ways to make power.
tree-farmer Steve unruh
Parallel run them if you want more flow volume.