Bingo, Ole' Ray here certainly has very good remarks to follow, all you can do is try it and see what happens. I run quite a number of different size diameter exhaust tube "Pitts" style mufflers on side mounted engines and have not had any pressure blow-back problems, but it does'nt mean that your Evolution engine wont. Some engines just wont work side mounted or inverted no matter what you do. Wish I could be there to work with you to resolve this, your losing valuable flying time. Keep talking to us here. MM