RE: OS .55AX in a Pulse XT 40
I've run the .55AX in three different .40 to .46 size trainers (a Sig Kadet, a Hanger 9 PTS Mustang, and a Midwest Aerostar/which my 8 year old flies) and the little bit of added weight is a non-issue. These planes tear up the sky (especially the Mustang minus training gear) with the .55AX's on the top end and will still float in for landings on the low end. You can't go wrong with the .55, I'll never buy another .40 to .46 size engine ever again.