Thanks for your efforts!.
Sometimes this disappointment come from the difference between indicated and true airspeed. Not sure if that’s the case here.
AFAIK speeds from POH are usually IAS. But I could be wrong, anyway, a discrepancy of 25kt is a bit too much imo. Thats why I wanted to speed up this beauty just a little bit
When you talk about cruise speeds or performance, these are almost always TAS. Only V speeds and normal procedures tend to reference IAS.
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This is a BIG improvement.
The RPM gauges do not work after installing your mod, can you fix them so I can make more precise tests?
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IOW, a discrepancy of 25 kt is expected since top speeds are typically at 10,000 ft or higher.
e.g. 140 kt IAS at 10,000 ft is ~168kt TAS, right on the money.
(I didn’t check the POH, just pointing out the discrepancy is likely very correct, this is most certainly something he would have gotten correct)
Good to know, I’ll do some more research. But after flying with other models and seeing that for the same conditions they weren’t that far away from announced cruise speed, I decided to do some tweaks.
Updated! A bit of code that was supposed to be there was removed by accident!
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OK let us start by saying the quoted cruise speeds for the aircraft are at 12000 feet and are TAS. Any testing needs to be done at 12,000 feet DENSITY ALTITUDE (not altitude above sea level) - 12000 feet no higher no lower.
Also, you should be using calibrated if possible, not indicated (though in many situations the two will be identical as calibrated just takes into account the effect of things like instrument error, deploying flaps etc, on the actual position of the needle in the cockpit).
But all that aside, quoted cruise speeds are ALMOST NEVER indicated, basically becasue that would be stupid and totally useless for navigation. On the other hand TAS, providing there is no wind, corresponds to your actual ground speed, something that is very useful to know. for flight plannng.
Cruise speeds are almost always TAS and usually at 75% or so power. Basically TAS adjusted for wind gives you the actual speed of the aircraft relative to the planet. TAS will be identical to groundspeed if there is no wind.
IAS and CAS are important but matter for things like approach speeds, Vr, stall, Vne etc. They are not useful for cruising and navigation.
Converting Calibrated Airspeed to True Airspeed accurately is not simple as it is effected by stuff like individual aircraft characteristics, OAT and density altitude. This is not the place to go into that.
The simplest way to tell if the MSFS 247D close to the book cruise figure is install something like the PMS gtn750 or maybe LittleNavMap and see what TAS they display at 12,000 feet (the 247D cruise altitude) at 75% power.
NOTE: Even if the original addon is correct (which seems likely) this is a game and there is nothing wrong with tweaking it for more speed, just be aware you are creating an “experimental” up-engined version of the original. However also be careful you do not end up cruising too close to Vne or the slightest turbulence and wind shear might ruin your day.
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Thank you very much for the detailed response. I’ll carry tests in those conditions whenever I have some spare time. I didn’t think about using LNM for reading TAS, good idea.
Something I also noticed in the base model is that when cruising at high altitudes (>10.000ft), as soon as you lean, RPM go crazy and you need to adjust MAP (around 15") to stay ~2000rpm. I’d like to know why this happens.
Did you adjust prop pitch ? When you (suddenly) lean at high altitude, you provide lots of power to the engine by the more powerful mixture. Then, the thin air at altitude provides low prop torque drag, so the power increase will indeed cause the prop will overspeed. Reducing MAP helps, but it is much better to 1) first reduce RPM by pulling prop pitch, 2) gradually lean as you climb. Start leaning from 3000 ft.
Yes, pulling prop pitch lever didn’t help at that point, rpm barely went down. Also being a supercharged engine I wasn’t sure what’s the procedure for leaning.
Yes, the RPM governer is unable to get away from prop overspeed.
Recommended for the 247:
Set MAP 32" and RPM 2100 for climb. Lean as you climb (60% rich at 4000 ft, 20% rich at 11000 ft).
Meanwhile slowly increase throttle to maintain MAP while climbing.
In cruise maintain 29" and 2000 rpm. Lean rich of peak.
Note that the B247D is hard to operate at altitude. She’s comfy at 4000-7000 ft.
If you do want go up high, make sure you allow for different oil for the low air temperature at that altitude.
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Now you make me want to fly it over the rockies in wintertime. Ready to crash and burn! 
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I’m wondering if anyone else noticed that the Vertical Speed Indicator only gives the correct reading between -500 and 500 fpm.
I made some improvements to the sound:
https://es.flightsim.to/file/61806/sound-fix-for-the-right-flywheel-in-the-b247d
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Thank you.
My main issue with the sound is the low bitrate engine sounds with lots of clipping and other distortions. Hopefully there will be a fix for that by someone or maybe by you. 
That’s weird because I do not experience any problem with the engine sound.
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The low bit rate is a fact, but not everybody notices it.
Last year I made a little comparison to highlight the difference between high quality engine sounds and what the 247D has:
The Goose has clear sounds, with a good differentiation between low, midrange and high pitched sound details, while the 247D has just one big muffled mush.
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I’ve never particularly liked the engine sound of the 247 in the sim, for reference: this is a video of the real aircraft
Oh and here is another video
Do notice how accurate the wobble pump sound is though!