Hi Annmarie , Respectfully, in relpy I am running a 4.6 cui Twin engine in this plane. Its an opposed design that has MUCH less vibration than a single cylinder large cui engine. Why do i need this much power? I have flown and raced some large scale bipes before and i just can't seem to get enough! I guess i'm just a horsepower junkie. Anyway , if you read my post you'd probably pick that i'm not too concerned about manufacturers warranties as i'm modifying the design and hence have no warranty claim anyway. I just think that when you release a kit or A.R.F. that you might as well face facts that someone is going to push the envelope re:design and power plant choice , remember you pays your money you makes your choice. As well i'm in Australia and i really don't think it would be worth my while sending a broken plane O.S. for manufacturers inspection if i modded it , broke it and wanted to cry foul , do you? I'm a manufacturer / designer in the automotive trade and i know only too well the liabilty laws and resonsibilities that go with producing a saleable product. I just think that i'll go my own way one this aircraft and take a little advice from my friends , who knows we might all benefit from experience if we're prepared to be open minded.