ORIGINAL: Jim Dines
What is it about the 40LA you don't like? For a trainer, it is a most ideal engine. What prop are you using. Mine does very well on an ASP 11X5 and 15% cool power. Mine is on a WM Mach I, a fairly large trainer, and this engine hauls it around perfectly as a trainer, teaches good flying habits and the plane is capable of basic aerobatics, including sustained inverted, inside and outside loops and even knife edge.
The OS 46AX is a terrific engine, but for a trainer? C'mon.....
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None of those maneuvers matter if you cannot take off from a grass field that hasn't been mowed recently, which happens at most clubs with grass fields from time to time. That is the failing of the OS LA series forties in contemporary trainers. Granted, once in the air, they (OS LA series forties) provide more than adequate power, but who wants to be at the mercy of the grass' length? The truly sickening part of it is that it doesn't cost a penny more to port these engines so that they will produce nearly the same power as their ball bearing equivalents.
I agree with Dave that the ST GS-40 is the best choice for someone pinching pennies. The ST GS-40 is a fine engine and needs to offer no apologies.
If a few dollars more cost is okay, the ST G45 or Thunder Tiger .46 is also a good choice, as is the Magnum .46. Lots of good choices.
Then there is the OS.46AX, as was mentioned by the original poster. This is a beautiful engine and is a good choice if the money won't be missed.