Let me start with my "mechanical idiot" point of view, then we will get the engineers to answer.
The first thing I recommend to anyone who is looking to upgrade from a machine with a #3 blower to a machine to a #4 blower is to measure your average hose pulls on a job for a week. Over the week if you average 150-175 feet per job, then getting a bigger blower is spending a lot of money for slightly faster drying times. If you average more than that, or want to do dual wanding, then it is something to consider. Don't get "blower envy" looking at everyone's bigger toys unless you can either afford to upgrade with no problem, or the types of jobs you are doing now demand it.
The next thing I like to tell them is you are going to get a lot of advice (and a lot of different opinions) about the effect of getting more rpms to spin the blower, or adjusting your vacuum relief valve from 12" to 14" or even higher. Both of those things will give you more vacuum - but you have to measure that against the cost - wear and tear on the engine and the rest of your machine. Asking others with truckmounts here is a reasonable way to get some good input on that, then balance that with what engineers and tech support at
HydraMaster have to say. Like I said, opinions differ even within our team.
Previous posters are right in that the
Boxxer 323 did come with a bigger engine (23HP vs 18HP) . However, even without talking to the Engineers, I am sure that it is more complicated than just swapping from the smaller blower to the larger one. Not sure about footprint, but the plumbing may be a lot different too. I will ask the people at
HydraMaster who are much smarter and wiser than me about these things on Monday.