Thanks for the Baron issue. My 340A has a horsepower increase from 310 Hp to 335 Hp per side and VGs with an increase in gross weight and lower Vmc, both done by the same shop. The issue of interaction, though obvious now, had never occurred to me. Time to dig through the STC files and talk to the shop.
One quibble regarding approach to Vmc demos. You mentioned the Baron reducing power to idle. I have "zero thrust" power settings we use for my plane. I would think idle power with an un-feathered prop could result in another significant variance in Vmc.
During WWII the U.S. Navy flew PBYs for max range using tables that had recommended power settings for the engines at specific weights. The flight engineer (remember those guys) would keep track of the fuel consumed, calculate the aircraft weight and reduce the power settings at least once an hour. They were flying very slow near the end of a mission. I'm guessing they were trying to fly at best L/D as the weight decreased.
Later, my Dad flew PV-1s and PV-2s without flight engineers, but the pilots used similar procedures ferrying across the South Atlantic.
I have a C340 Ram VI and a T-34B with IO-520s. Both are fitted with GAMIjectors and JPI electronic monitors. I do run the T-34 LOP for ~5 years and use ~10.5 gph compared to ~12.5 gph ROP without problems. I have made flights at 9 gph, but the airspeed really drops off.
I do not run the 340 LOP. When the ROP/LOP discussions started, I spoke with the RAM people. They said they had no experience doing LOP and implied that if I wanted to, I could do the experiment for them. Naah, those engines and turbos are expensive and nearly new.
I operate the 340 at ~55% power, getting average GPS logging of 182 Kts over the past 10,000 Nms at 16,500' - 17,500' burning 31-32 gph at cruise. I could burn a LOT more, but don't see a reason to.
