I apologise in advance if this is a "dum-dum" question...

I'm trying to improve the fuel economy of my '86 245 w/m46. Have done a basic tune-up involving cap, rotor, plugs and air 'n oil filters (needed to be done anyway) and cleaned the flame trap. It is consistently getting 23-24mpg with a mix of city and highway driving. I was reading some posts where other BB'ers claimed they were getting 26-27 with automatics.

So I figured that maybe it has something to do with my driving style. I usually upshift at about 3000rpm and downshift when the tach drops below 2000. Occasionally, I let it wind out to 4500 in second gear when I need to accelerate quickly to merge with traffic on the interstate.

There really isn't any power available below 2000rpm, or maybe that's just my perception. It seems that the usuable powerband is between 2000-4500rpm.

I recall reading on the BB that the valves "float" above 4500rpm or thereabouts. What exactly does that mean?

Is there any danger in running it above 4000 on a somewhat regular basis?

Below what rpm is one "lugging" the engine?

Thanks for putting up with my incredibly stooopid questions, but I figured that if I was gonna ask this would be the appropriate place. :-)