Steve, WOW, since the build its been a long time for an old fart like me but I will see if I can remember some of the changes I made. First I would like to say that there are many changes that I would still like to do and have just not taken the time to do, so really I will just share my opinion on some that I did and ones I feel would possibly help. Just remember that I am no engineer and these are MY opinions. So please do not throw things at your computers because of the idiot talking. First off a friend of mine and I experimented with the wing strut fairings. I can honestly say there is a major difference between streamlining and round when it comes to this. I believe the ratio is something like 10/1. Just knowing this ratio I tried to get as many antennas out of the slip stream as possible. The wheel pants were fit as close as possible and as low as possible to try and save on some drag. Don't really know if this helped much and I would not have done it if I thought I would be flying off of a lot of rough areas. I fly off of my own grass strip but I try and keep it rolled well.
Another area that I feel really helped was I fiberglassed in some foam on the inlet side of the cowl. By this I simply tried to create a smooth, non turbulent area as the air comes into the cowl. I spent some time on the jury struts and the tail supports as mine came from the factory and were round, so I converted them to an airfoiled shape. This was done just like the wing struts by glueing wood to the aft side of the piece and sanding it to an airfoiled shape and then covering with fabric and painting. I did this same thing to the landing gear as it goes up into the middle of the fuselage. Many of you were supplied airfoiled shaped ones from the factory. You are so lucky.
Another area on my kit that was lacking is the area around the horizontal tail where it mates to the fuselage. I made my own fairings and attach points to allow this to be an area of less drag. A cosmetic area that I did not like was the fact that the earlier kits when built the way the manual tells you is that the prop center line was not in the center of the cowl opening. I simply hung the engine and changed the cowl allignment to look better. Since I live in Kansas and it gets very cold here in the winter and hot in the summers, I built a cowl door that I can shut to cut down air to the radiator when needed. I was not the first to do this as I took the idea from a fellow builder. Because of the temperature changes here I designed a sliding door system to cut airflow down on the oil cooler. With these two devices it really allows me to adjust the engine temps while inflight. Not really speed mods but they are nice.
I know I have forgot to mention some of the mods but really many of your kits were shipped to you with these already done. Mine was just an early kit that needed the changes as the speedster was just coming of age. Sorry I know I am rambling on and on, so I will shut up and listen to any comments others have about these great airplanes. And thanks to all for the nice comments about 912KS.