I'm not sure how to go with my set up. I have a GS40 katana with an OS 46 AX with the CG set up at 130 mm. It flies awesome but thinking I could save some weight and add a little power I bought a Macs muffler for it. The Macs is about 2 oz. lighter and I found now that my CG is more like about 160 mm. The rx battery was at about 1/2 aft of the trailing edge of the wing to get the CG to 130 now I have it up by the fuel tank and it's still not enough. I'm thinking I could move the engine forward a little but I don't think it will help that much. I don't want to add a bunch of weight to balance it out. Any suggestions? Here's the muffler I put on it. [link]http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ652&P=ML[/link