I have a dle85 in mine with a 24x14 prop but I will never go bigger than a 60cc ever again. All you do is chase vibration problems. A friend of mine uses mostly all dle55RA engines and he is always flying and I'm always fixing cracks. I think the 55RA is the perfect engine for these giant top flite planes. I am currently building the top flite zero with the dle61 but I have had to butcher the cowl because its a side exhaust. That rear exhaust on the 55RA makes things a lot easier. He uses the Bennet Mufflers instead of stock. As for the four blades, I tried it a Biela 20x10 once on a 60cc and screwed it to the wall of my trailer for decoration. I like my warbirds to be pretty fast and the 4 blades aren't.