An old thread I know but....

I can't say I'm familiar with all of these engines but I have a few of them.

The OS LA engines are incredibly reliable engines with solid performance but are far from the upper end of the power scale. If you want max power this isn't the engine.

I've had both the 46AX and GMS47 and can say they are both similar in performance. The GMS seems to be more peaky than the AX and both have problems running at low throttle settings for extended periods (not a cruising engine). The GMS is probably less happier engine at very low throttle settings. Oh, my GMS47 doesn't like sidemounting either.

There are some things I don't like about the 46AX. Those damn muffler bolts break at the head or drop the nut off the end. The higher revs you run (depending on prop size) the more likely the muffler is to fall off. In the last two weeks I've lost one muffler half and just managed to retain another (3 times). Another issue is they tend to eat bearings if given a hard (but not excessively so) time. I know of 2 46AXs which have chewed up pistons thanks to bearings progressively failing in flight, mine was one of them. Replacement pistons/liners are prohibitively expensive, just buy a new engine.

Another engine to consider is the 55AX. It is very similar to the 46AX but has much more torque. Thus you can prop it to wail (12x6) or go practical (12x8). With the larger prop you'll have similar top speed and can use that torque down to pull the plane around cleanly at low speeds the 46AX struggles with.

My Strega has run both a 46AX and 55AX, both make the plane scream. The 46AX isn't capable of holding vertical indefinitely (with any prop) but it still scoots along. The 55AX can get my plane it into flutter during a dive (if I don't watch it). The 55AX with 12x6 MAS has unlimited vertical, the 12x8 MAS will hold a short hover and then fall out. Obviously, what plane you fit the engine to will make a difference but that should give you an idea.