There are too many variables to make an exact calculation, I remember prochem used to say in their marketing and I have seen it many times on truckmount owners vans... '20 times more powerful than portables machine ' but I don't think this is true.
I'm sure I have seen on the USA forums portable manufacturers have put a measurement instrument on the end of a 100ft of vacuum hose and measured the difference, but I can't remember the exact result. And theses results are always slightly suspect because they are not done independently and its in the interest to of the portable builder to show their machines have the power of a truckmounts.
I like to look at it from another angle, how much power you can pull out of a domestic electric socket which is a maximum of 3hp ( maybe slightly higher in some homes) so if your machine has 1 plug it cannot be higher than 3 HP ( slightly less as some of that power will be used by the pump) so 2 plugs will be 6hp...,, 3 plugs 9hp...... etc ......etc ...... etc
Now look at a 24hp truckmount, even if it has a big pump pushing out 1000psi ( which uses 3ph) then you still have 21hp left to drive th PDB vacuum unit which is 7 electric plugs worth of power.
Of course this is just theoretical and working on a truckmount working at 100% efficiency using the total energy available and my theory is biased as I'm a TM owner I'm sure a portable owner will have his own mathematics to prove that a portable has the power of a truckmount, but I would be interested in how he pulls more power out a electric socket than is available.