For years I have wondered whether or not flap gap seals would be a good speed modification to do to my airplane. when I first tested one years ago that had them, I was alarmed that we had lost our fowler flap slot and cove covers in the wing.  Checking with the wing designer he said not to worry.  Sure enough, stalls were normal-- approaches normal-- I could see no difference.  So to apply this principle to mine, I thought maybe I could remove the cove covers and put a strip of aluminum that the flap would come up and seal against.  But I wanted to test it first.
 I had just flown my airplane two hours to a out-of-state location and I had taken some good data.  So for the return trip, I purchased some good tape material and completely sealed top and bottom on my flaps. You would think it would be at least 2 kn increase , right?
I stopped at 12.5 and 14.5 (the two altitudes where I had exact data) and the indicated airspeed was............exactly the same! Go figure. 
I  have a couple more bright ideas.  I want to try some rudder gap seals. Didn't want to do it up to now because of the paint, but I guess I could try it-- and if I get 2 kn or better out of it I will get the airbrush out and paint them on the bench.
And then there's the fuselage/horizontal stabilizer fairing I have in mind????????????/ AHHHHHH the quest for speed, maybe an extra hundred horsepower would do it.