Swirl throttle was installed just before impeller in Mikulins and Jumo 213s, also on the DB 603L. Mikulins and Klimov engines have had carbs between impeller and cylinders, it was not much of trouble to install the swirl throttle on fuel injected engines.
More about the stuff:
http://www.ww2aircraft.net/forum/engines/superchargers-mikulins-klimovs-jumos-etc-40086.html
I would call these a variable inlet guide vane, they would allow a degree of variability of the supercharger outlet pressure without the impairing of efficiency caused by throttling the air flow or the possible complexity of variable speed drive. Interesting that the Jumo 213 incorporated them.
They were known to Daimler Benz.
http://www.ww2aircraft.net/forum/en...628-a-28270.html?highlight=daimler+benz+DB628
The DB628 (a DB605 derivative) had a two stage supercharger.
The second stage was transversely mounted as usual in DB and Junkers A12 engines but the first stage was mounted coaxially to the gear box and had a variable inlet guide vane. It seems both the inlet guide vanes and impellor was variable pitch. The large size reflects that the engine was meant to operate at around 50000ft and would be taking in very thin air.
The 627 was a version based around the 603.
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