Interesting thread.

The 46 LA and the 46 Irvine aren't really in the same class. The Irvine is a respectably powerfull BB sport engine, while the LA is a simple low-cost entry-level engine (& the least powerfull 46 engine currently on the market). While the 40/46 LA engines are schneurle ported, they lack boost transfer ports -- this is the primary reason for their weak output (it has nothing to do with ball bearings, or the lack thereof). For example, the very similar TT 42 GP has a boost transfer port & is substantially stronger than the 40 LA & easily matches the 46 LA, despite having the same small carb-throat size as the two LA engines.

Raven, are you running at high altitude or at high ambient temps? I have consistently measured fresh OS 40 LA's @ 12,000 rpm with APC 10-6 props on 10% nitro, & OS 46 LA's @ ~13,000 with the same prop. Yours seem weak in comparison, particularly the 46. I have measured 46 LA's @ 10,900/11,000 with APC 11-6 props (to much prop) --- something seems to be amiss with your 46 LA. I have also seen little change in the output of those engines with varying nitro content. They run well on anything from 5% - 15% -- giving similar output.

If the 46 LA is reasonably correctly propped (9-7, 10-5, 10-6, 10-7, or 11-4 are good choices), it will work as well as can be expected.