wrong interpretation of numbers:
the weight of the 801 given here above, is the POWER-EGG weight, what means, the weight of the engine ready to bolt on the Holder, armored oil-tank/cooler and cover panels included, simply add 55l of oil, attach control wires et ready is the engine!
Now for the 2800: add all the necessary tanks, engine covers and oil and compare the weight..and if you use the corsair as reference, add the weight of the compressor,intercooler, etc,etc...
You can't compare a dry weight/power ratio, because no engine can devlop power at DRY weight, it's just metal scrap without use.
Only a comparaison of ready to use engine(with all it's secondary equippement) can be applied.
You are quite right that the comparison of the ready to use engine would be the best way but that information is usually impossible to find.
As for the BMW 801 I have one book that says it's dry weight was 1940lb for a "D" model but it is a war time book and I have seen no other source to back it up.
the 1946 "Janes" gives weights of 2,669lbs for the "A" and 2,702lbs for the "B" which may be for the power egg. It gives 2321lbs for the "C" and says it is a bare engine but bare may not be the same as "dry" weight.
If someone has any German data sheets or manuals that give weights it would be much appreciated as I think many websites are not clear or are repeating information with their own interpretation. Trying to translate such things as "dry" and "bare" can be tricky.
The dry weights come from the engine manufacturer and the engines are about as stripped as possible without being totally ridiculous. Since everybody at the time knew what was going on it was no big deal.
As a for instance the American Allison engine included 10lbs of exhaust flanges, gaskets and nuts in it's dry weight but the exhaust stacks were the responsibility of the airframe manufacturer. The stacks were welded onto the provided flanges to suit what ever cowl shape the airframe manufacturer decided on.
Various accessories were "optional" such as generators. The British (and Russians) got into trouble with the early P-40s because the British had specified a 1500 watt generator on their planes instead of the smaller unit on American planes. Not only did it weigh more but the increased load on the drive gears caused numerous failures. Gun synchronizers weighed about 4lbs apiece.
Starters were another "option", yes you need a starter if you don't want to turn it over by hand or use a Hucks starter but do you want an electric only, a hand cranked inertia starter, a electric inertia starter with hand crank option or do you want a cartridge starter? And some countries had more than one starter supplier even of the same type.
you could easily add several hundred pounds to an Allison engine before you fitted a propeller, added any fluids or fitted engine mounts and a cowl to it.
dry engine weights usually included the ignition harness, the carburetor,a fuel pump and if needed a water or coolant pump.
The ignition harness bit is interesting because small planes of the 30s and 40s often did not have radios and so an ignition harness that was shielded for radio use was an optional extra over a non-shielded harness. The shielded harness weighed more.
getting back to "Only a comparaison of ready to use engine(with all it's secondary equippement) can be applied." in a more direct fashion, I can give two comparisons from " Development of Aircraft Engines" by Robert Schlaifer and "Development of aviation Fuels" by S.D. Heron.
1. The comparison of the Merlin and the R-2800 I mentioned before.
Including everything except fuel tanks the Merlin installation in a Candair DC-4M weighed 3,980lbs while the R-2800 installation in a DC-6 weighed 4,087lbs. a 2.7% difference. The R-2800 had 70% more displacement
and 35% more take off power. At maximum continuous power on low blower (low altitude climb) the R-2800 had about 20% more power at about the same specific fuel consumption. there is a bit more.
2. there is a comparison of the Merlin in the P-51 and the R-2800 in an F4U in early 1943. Both with 2 stage superchargers.
Again with out fuel tanks.
.................................................................... Merlin.............................. R-2800
Engine with
charge cooler..................................................1,639lbs........................... 2,517lb
Cooling system with coolant
includes oil coolers............................................. 652lbs................................95lbs
_____________________________________________________________
total engine weight with
cooling system ........................................................... 2,291lbs .........................2,612lbs
Engine mount &cowl.............................................284lbs............................303lbs
Cooling system mounts,
control mechanisms and/or cowl flaps.......................116lbs............................101lbs
Intake exhaust, starter, control
propeller controls.............................................. 624lb............................ 681lbs
________________________________________
total associated weight..................................................1,024lbs...........................1,085lb
_______________________________________
Total installed weight.................................................... 3,315lbs..........................3,697lbs
I will freely admit that these comparisons have nothing to do with German engines.