hi, One thing I was told was to break in the engine as it came from the factory and then open it up and clean out the case, metal filing do build up. then rotate it and clean it out again after your happy with the tuning and several tanks of fuel. what i did was rotate the lower half 90' to the right so the exhaust is still on the bottom. It is mounted in a top-flite corsair. I asked Kondor Model Products this same question and they told me it can be mounted it any position. I just did not want a big hole in the top of the cowl. the vent is on the side as well with no problems, I think having the vent on the side keeps some oil in the case to keep the gears lubed up and keeps them cool as well. Also, starting this engine does get easier the more fuel you run through it. hope that helps.