In performance the D was great at low and mid altitude but had the same handicap the A models had at high altitude. The power loss with altitude was not as bad as the Antons but not far off.
In my opinion the whole inline engine experiment was a bad road they went on, because sometime in 1943 they had to stop development of piston engines that were not in production.
With this move they lost two aero engines that had the potential to change something when it mattered the most.
Right after introduction of BMW 801D in production and getting it installed in the FW-1`90 the BMW team started working on a replacement.
It was called BMW-802. was similar with the 801 but had 18 cylinders instead of 14. Two rows of 9 instead two rows of 7.
there are some pictures of this engine around:
And some specs:
18-cylinder supercharged two-row radial engine
Bore: 156 mm (6.14 in)
Stroke: 156 mm (6.14 in)
Displacement: 53.7 L (3,280 in³)
Dry weight:
Components
Valvetrain: One intake and one sodium-cooled exhaust valve per cylinder
Supercharger: Gear-driven single-stage three-speed
Fuel system: Fuel injection
Performance
Power output:
1,912 kW (2,563 hp) for takeoff
1,176 kW (1,575 hp) at 12,000 m (39,000 ft)
Since the FW-190 with BMW-801 was so successful in early stages the work on the 802 went really slow, and was 1943 by the time they had the engine in testing.
The 802 was impressive in what it offered. It was rated at 2600HP for take off and was said it could easily reach 3000hp during it's life.
The most impressive thing about this engine was the high altitude performance obtained from a gear-driven supercharger. The engine could reach 1600HP at 12000m. This is a lot of power over the old 801 with only about 30% increase in weight.
This engine
IF They kept working at it like they did with the 801 could have been put in mass production in 1943.
Now if you install this thing in the ,let's say, FW-190 A6 airframe. Extend the wings a little to bring back the wing loading to A2-4 standards, You have on your hands an aircraft that could have done it all for the LW. Low altitude fighter, Jabo, Mid alt bomber intercept and High altitude fighter and all in between. Could have been right there with the very best of them at any altitude.
The FW-190 airframe was well built from the start and could have worked with that engine with only minor changes.
This thing could have retired the Bf-109, and that would have allowed them to produce, maintain and upgrade, a single piston engine fighter aircraft all over the map.
I'm sure they could have produced a lot of them if they concentrated all resources wasted in making and upgrading the fw-190 A, FW-190D, Ta-152, Bf-109G14/14 AS, G10, K4, and all those old engines they were trying desperately to get more juice out of: BMW, Jumo, DB-601, DB-603.