Jaime is so right about restriction. I owned two truckmounts both had 45 Roots blowers.I think all our tm's and portables, all of them comes to have less restriction. the less restriction the best.
When I see a machine with small opening to the tank, or a 4 in inlet blower the hose to got the tank is 3 in, so there is restriction right there.
Same with a ETM or portable, the best is when the motors are direct mounted to the tank. can be the same motor but the design is what makes the difference.
One had a 22HP Kohler turning the blower and its Hypro pump while the other had a liquid
cooled 20HP Vtwin. As far as the plumbing one had 3 inch from blower into tank and
31/2 going out with large hose to filter box with 2 vac inlets while the other had two 2 inch vac hose from a fitting on the blower then into the waste tank. The first one just had better air flow going
in and going out of the waste tank. Also the silencer on the first one was a lot bigger than
the other. Both had tachometers and we often used these machines together when doing
large commercial jobs. The truckmount with the superior plumbing could operate turning
the blower at 2950 rpms and actually be better than the other which was not bad at all but
to keep up the one with more restriction had to operate as best I remember at 3100 rpms.
I found that almost unbelievable but with these bigger truckmounts air flow and low restriction is huge in vacuum performance. They both operated right at 14HG. The one
with more restictions did provide more heat however but not a lot.