Since we're talking LOP...
My old RV-3 (O-320 carburated, not tuned, 150hp, climb-pitched wood prop, fuel-totalizer, no MP, 25g tank). I usually cruise at very low power settings (2,100-2,300 rpm and high altitudes 10k-12k). I did this for a couple reasons, I loved flying that plane, it's not all about getting there and I'm cheap. And the third reason, oh yah, I'm just cheap!
First I understand that at these power settings it's basically impossible to "hurt" the engine. Can't detonation/pre-ignite. So I played around with mixture a lot. One thing I found was that once you hit "rough" you where pretty much done withe red knob, nudge it in a couple MM and that's as good as it gets. If you continue leaning to the rough, you loose power, you can make up for it by increase MP, which in turn used more fuel. Net result: "in the rough" net fuel flow = airspeed. But typically I could reduce fuel flow by at least a GPH until rough and CHT/EGTs did all the things they are supposed to (increase).
I added FI to the RV-4 I'm building now specifically to tune the injectors and run LOP, cruise cooler and better. I'm interested to see how different it operates in this area. Can anyone describe "extreme lean" on a ballanced engine? Does it just "fade" without the roughness? I think in theory; continued leaning of a perfectly ballanced engine should just smoothly loose power till it stops running.
-Bruce