Interesting, but I don't think there is an induction leak. Operations are normal on the ground and on climb, even initial cruise, but after a while the prop lever must be set fully in to maintain 2300 rpm, which is recommended cruise. Throttle is set at this point to 25 inches, and fuel flow adjusted to 14 gph, giving a nice high TIT. No problem except for the prop selector needing to be fully in.
On descent, the rpm drops further, no matter the other settings or speed.
On final, with the prop fully in, a small amount of mixture leaning, and around 15 inches of manifold, the rpm is down to 1000-1100. It seems to be an accurate indication, this is the second rpm gauge fitted, and you can paractically see the blades.
If a go around is flown, the engine recovers quickly, although the rpm never gets to 2400, which it would if it were a normally aspirated engine.
I don't like not having control of the rpm. I can't complain about the power output, it seems to be adequate in that the airspeeds and climb rates are normal, or close to normal. I guess this is just a feature of the turbo normalisation.
I would like to know if anyone else has flown this type of setup in this airplane if they have seen similar low rpms, especially on final approach where I would have expected the airspeed to keep them higher, even if the throttle was fully closed.
I have had two occasions with this engine giving moderate vibration and a lack of power in flight, needing an emergency return to land. I think they were the loss of upper deck pressure, although the mechanic fixed them by cleaning the plugs and injectors and it is currently running smoothly. Don't know if this is associated with my suspicions or not, and again I am looking for what is considered normal for this engine and airplane so that I can decide if there is something wrong.