I just tried something over here and I think I may have stumbled on a good idea. Like many who post here, I have a 1 zone system and I futz with things to get more air upstairs as it gets warm in the summer (stat is downstairs). Downstairs I have gobs of air flow.
Today, I pulled off one of the supply covers upstairs and noticed the air flow increased dramatically. This got me to thinking - how do I get this flow going w/ the cover back on?
Since my system has dampers installed in the ductwork, I decided to pull the COVER dampers off. You know, those flaps that open and close w/ the little lever on each cover plate? My thought was every little bit of resistance on these covers seems to put a dent in the flow. I replaced the cover and I did notice better air flow going through the grate. So I then went and pulled the flaps off all the registers on my top floor. Better air flow all around, and my downstairs is still blowing strong. I guess perhaps I'm not leaking air out of the trunks now due to less resistance overall?
Any how, I thought I'd share my experiment in order to get some feedback from everybody. Maybe this can help somebody else. If there is a good reason to NOT do this, pls. let me know. I can put the covers back together.