Indeed, it’s M20K, lot of models with 210hp-220hp goes there 231, 252, TSE, Rocket, Encore…all should true at 190kts with 3GPH less than Panthera
The Encore is the most refined product being FIKI with +1150lbs useful loads, these are rare birds and there are not that many around: one hangar nighbour in France stopped flying and sold it: she flew to New York one week after he posted in one US website that he is selling it 
A friend of mine used to own an M20K in a hangar next to mine. He was consistently 10 ktas below book, but he had a 3-blade prop, maybe that was the reason?
@terbang has been flying one of those too, and extensively for that matter. Perhaps his experience is closer to book?
I just want to ensure we are comparing apples…
We still fly it 🙂 Ours was Encore-converted three years ago, i.e. has a TSIO-360SB with 220 hp now. It doesn’t quite make book numbers either but it’s not ten knots that are missing, rather around five. It has a three blade prop and many antennas all over e.g. for the panel mount satellite phone and the active traffic system. I guess, these are the reasons but these modifications were done before we bought it, now over then years ago, so I can’t tell for sure.
Three to five knots below book values is not uncommon in my experience, but ten knots is a lot. Maybe the plane you mention had other issues, e.g. poor rigging?
I had the same issue with 2 tb10 of a renting agency. The first one was resprayed, nice interior, correct engine and a nice 3-blade prop. The second, old and rusty as hell, dirty inside outside and poor paint, 1 less antenna, and 2 blade prop. The old one was producing book figures, whereas the good looking first was at least 5 knots slower…3 blade props are less efficient and heavier, which implies higher drag of the stabilizer.
greg_mp wrote:
3 blade prop
Look no further. I flew a M20J (2010) ages ago; it initially had a two-blade prop; then was converted to three blades to get an enhanced noise certificate when it became fashionable to severely restruct operations on weekends if you did not have one. Lost around 5-7 kts cruise speed in the process with no other changes made to the aircraft.
No such loss on the TB20 going 2B to 3B. One wonders what else is going on with some other types.
Cobalt wrote:
Lost around 5-7 kts cruise speed in the process with no other changes made to the aircraft.
These are real numbers from 2B to 3B:
These are the deltas on 75% power cruise on high rpm where things gets noticed
At 55% economy cruise on low rpm 2B/3B does not matter that much, 2kts?
Lost around 5-7 kts cruise speed in the process with no other changes made to the aircraft.
I’m sure that @Mooney_Driver can sing a song about the matter 
In the RV world, comparative data has shown the same loss, 5-7kts in cruise for the RV-10. This being usually compensated by a shorter TO distance and better ROC. And less noise.
My plane has a 3-bladed MT constant speed electric prop for which there are no ‘book’ speeds. It certainly does not outperform the book speeds for the fixed pitch McCauley with which it came equipped from the factory. I’ve flown another example with a 2-bladed McCauley hydraulic CS prop and it was much faster, more than ten knots. Some of that speed advantage however came from 160 versus 150 HP and a 40 year program of aerodynamic tweaks on that particular plane. So who knows if the prop made that much difference.
