DB turbocharged engines DB 623 and 625
 

Does anyone have specific info on the reasons why DB failed to develop in-service versions of the 623 and 625? And I mean specific engineering reasons, like possible bearing failures etc (no generic stuff like "lack of heat resisting alloys")

Re: DB turbocharged engines DB 623 and 625
 

I don't have much in specifics, but suspect that the cancellations of these engines was aimed at freeing up resources to concentrate on more immediate goals, such as resolving reliability issues with the DB 605, DB 610 and DB 603. In the same time frame (January-April 1943), there were several other engines that were abandoned:

DB 609
DB 622
DB 624
DB 629
DB 630

One thing that does stand out is that aside from the DB 609 and DB 630, the engines in the above list featured turbosuperchargers. Also, the subsequent DB engine developments that reached or came close to production mostly seemed to be based on mechanically driven superchargers. The only exceptions were based on the Hirth turbosuperchargers, which were basically intended as auxiliary superchargers for engines with standard single stage mechanical superchargers that were already in production. This probably appeared to be a quicker and lower risk approach. I have seen statements that one of the major problems with the Hirth turbosuperchargers was that the exhaust ducting tended to burn out quickly (I recall a reference to a lifetime of 25 hours).

Another consideration is that some of these engines were were designed for extreme heights (~50,000) feet and it was probably realized that, at best, any results would be achieved at the cost of considerable effort and delay and that the threat of large scale enemy operations at such altitudes was appearing increasingly unlikely.

Robert

Re: DB turbocharged engines DB 623 and 625
 

It is a pity that DB couldn´t make their turbochargerd versions work for their purely turbocharged (i.e. no mech stage at all) would have provided considerable power benefits at all altitudes as testified by P&W´s VDT design. It is wholly misleading to see turbochargers as only high altitude devices.