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The point is timing.
Jumo 213 was ready some time in 1944, so if a two-stage 211 can be introduced in early 1943, the Germans had the good horse to bet on.
The question is what kind of power can the engine withstand?
For instance, let us say that engine "A" can deliver 1200hp to the prop at 8,000ft. It is using up 100hp in friction (piston rings, bearings, cam followers on camshafts, whatever plus pumps) anad it's supercharger is taking 100hp to run so the engine is actually burning enough fuel to make 1400hp.
Adding a second speed to the supercharger could take another another 100hp so the same strength engine can only deliver 1100hp with the second speed engaged. Adding a second stage could suck up even more power. the engine might only give 950-1000hp at 24,000ft with the second stage engaged. This may give an extra 150-200hp over the original single speed engine but might not be what you are looking for.
Merlins and Allisons with two stage superchargers often had strengthened parts to allow the indicatedHP to up so as to take full advantage of the extra boost available at low altitude. Of course the extra boost can only be used at low altitude if the fuel will allow it.
Junkers engineers may have had choice of working on the 213 or a new supercharger and strengthened parts for a late series 211 but not both at the same time.
If we add a two stage supercharger to the engine to try to get 1200hp at 24,000ft the second stage make take another 100hp to run.
Why is that a problem?
DB603 engine height and width were small enough to allow easy fit in a fighter aircraft. Certainly a lot easier then radial engines such as the BMW801 and R2800 which required a large diameter fuselage and considerable space behind the engine for cooling airflow.
The Me-109 requires the DB601 / DB605. So complete replacement of the DB601 with the DB603 means replacing the Me-109 fighter aircraft with the Me-309. Or else Fw-190 airframe production doubles and the 20,000 additional Fw-190s are powered by DB603 engines.
I think the Me-309 and Fw-190C (i.e. DB603 engine) would both be bad news for the Allies.
Surely a two stage supercharger will require less power to make a given amount of boost at altitude? Or more boost for the same consumed power.
What's the point of a 2 stage Jumo 211? The Jumo 213 is essentially a tidied up and improved version of the 211 anyway.
Junkers Jumo 211 - Wikipedia, the free encyclopedia
Junkers Jumo 213 - Wikipedia, the free encyclopedia
There seems to be a huge leap in weight to go along with the added performance. Maybe required strengthening to get the results?
I should think that the Jumo 213 would slip onto the production lines of the 211 relatively easily.
The Me 309 was killed because it had more engine power but not really more speed than the Bf 109G it was intended to replace. Maneuverability wasn't really better than the 109G as well.
The DB 605 was developed because the 601 reached performance limits with the 601E series (both rpm and boost pressure), the intention was to optimize the 605 for mass-production and mild power increases from increased capacity at similar or slightly higher boost levels (to stay on B4 fuel).
That misses the point. The fate of German aircraft programs was largely decided by engine availability.Me 309 was killed because it had more engine power but not really more speed than the Bf 109G