Firstly, i hope I am posting on the right forum.

I am busy building a Swallow EX90 and have the option for either a 2 stroke OS91FX with tuned pipe or a 4 stroke FS120S III.

I have no practical experience with these two motors and would value any input in this regard. I am not in the States and in our classes for pattern in my country, these are the two max size options one may use in the class I will be flying in (probably the States version of Basic class) and am situated at the coast in our country.

From what I have heard from others so far:
1. 4 stroke will give better throttle response over the range as opposed to a 2 stroke with tuned pipe.
2. down legs on maneauvres and landings will fair better with the "prop brake" provided by the 4 stroke.
3. since the FS120S III has a pump and is not reliant on exhaust back pressure, one can place the fuel tank on the CG point thus stabilising CG during flight.
4. some have said the 2 stroke will give better vertical performance???
5. Mounting the 4 stroke upside down can give idle problems (2 stroke to be mounted at a 60 degree angle)???

Your opinions would be appreciated since I am now in a quandry as to which direction to go. Cost difference between the two options is negligible

Thanks

JR