So given the fact that (as you mentioned) you are going to be living at 1/4 to 3/4 99% of the time and its agreed we are talking about a very narrow range where it is going to come into play (and that is assuming all is well and everything else downstream), why don't you just go with the Dynoman's recommendation to run separate K&N filters?I guess the next question is, how to use the CRs velocity stacks while ensuring adequate filtration but allows enough air flow
I think "sometimes" keeping the airbox is overrated. If you just make sure they get a sufficient supply of clean air and it enters the carburetor through some sort of velocity stack (or whatever you want to call it) that won't create a whole bunch of aerodynamic fungus that will upset the apple cart.... (ala the CB750 syndrome) then all will be well with the world. I think delving too deeply into things in your situation is like chasing moonbeams. You will have to spend a kings ransom on donuts to realize any gain assuming there is any to be had.
Personally I would just buy 4 good quality individual filters and hopefully the Dyno guy can tell you exactly what works and back it up.
Just on a side note.... and it really doesn't belong in this thread. My GL500I has different length intake manifolds. the runner diameters are equal, the runners in the Y shaped boot between the carbs and the airbox are equal length and there isn't anything anything in the airbox that is of any real interest. So there you have it... different runner lengths.
If you were running a LSR bike it would be a different story, but as it is I think you are better off taking their advise and spending some of that donut money on one of those A/F setups because I believe it will come in handy. You might still want to do some slight changes after the dyno setup just to address any real world drivability issues. I'm talking through my hat a bit there, because I don't have any firsthand experience with any of those kits. I am going to buy one as I'm starting from scratch and it'll probably pay for itself more than once. I'll let you know how it works out, but it won't be until after the monsoon season.
I may have missed something in this thread, but my ADD prevents me from re-reading it, plus I haven't had my second cup, so apologies if any of this is redundant or moronic.... .
You should probably not take any advise from someone who uses intake manifold spacers like this.