I replaced an old OS .40 FP in my Tower .40 trainer with a .46 Magnum and have a few questions. I have moved the battery back behind the servo tray in an attempt to get correct CG but it looks like I still need a few more ounces of weight. Where is the best place to add weight and does the battery need to be in foam? I was thinking about velcoring the battery directly to the fuse floor.

You could use a servo extension and move the battery pack really far behind the CG to reduce the amount of weight you have to add.

The battery pack should be padded. We sometimes wrap them in foam, then wrap that with clear packing tape. This can be glued to the inside off the fuselage with shoo-goo. To remove, just cut through the tape.

I used a small bit of lead right under the vert stab. Worked great. No underpower issues because of it. I also moved my pack back but it wasn't enough. I am not a big fan of putting my pack in the tail. But that is only personal preference. One more extension is one more possible weak spot IMO. If needed, solder a longer lead instead of using extensions. Makes for a better piece of mind.

with this more powerfull engine fitted you should be right to position the battery pack where you have it now but wrap it in foam and secure it so it doesn,t move, any extra weight needed should be put at the very rear of the fuselage, grab some car wheel stick on lead weights and cut the sections off to the required balance. when your happy with the cog you should fasten the lead with a screw.

I cut the covering off a side of the fusealage both fore and aft of one of the rear formers. I think I can put the battery just in front of the former and the weights a little behind the former to balance everything out....so much for the fancy covering job!