The first one I built and flew had the Saito 91 in it. I mounted it sideways and did have to cut the cowl slightly to clear the rocker covers. That plane and engine combo is a good one. The 1oo would do well on it. I was running a 13x8 APC.

The next three that I built had the 61 FX. The fourth was mine with a 12x6 APC. It doesn't pull quite as good as the 91, but still flies it well. People comment that the 61 2 stroke sounds more realistic than the 91 4 stroke. But the 4 stroker does sound good on it.

I prefer the 2 stroke with the Top Flite muffler over the 4 stroke install. But that is all personal preference.