Bud
I was aware of the Keleo exhaust extensions. I didnt go for them because I was concerned about clearing the inside of the cowl. The angle of the exhaust pipe has to come close to the engine crankcase to stay inside of the cowl, especially for the left cylinder which is offset closer to the prop by a small amount. They look like they have the right shape, but the actual dimensions are key. Also, where they come out of the bottom has to be right. The only way to find out is to buy one, kind of expensive experiment. I got the blue silicon tubes from a hobby shop, they are used to attach tuned pipes to mufflers. They come in various sizes. also had a little trouble getting the full throw on the aerilons, I compromised between making a grotesque gap or less throw. I got about 1 1/4 ". My Sig 1/4 scale cub has been flying well for years with less throw than that. If you mix in rudder, the result is even better.