Effects of multi-speed superchargers (or lack of the same)

[xylstra]

Much has been discussed here of multi-stage superchargers, but less of multi-speed single-stage superchargers.

The DB engines used a hydraulic fluid coupling with a barometric control to achieve multi-speed drive with a seamless power curve.
Other engines featured multiple speeds, kinda like a stick/manual/standard shift transmission in a car, with a jagged power curve.
The V-1710 was stuck with one speed.

- Wasn't one reason for using the V-1650 in the P-40 because it had a 2-speed drive?
- Could an excellent multi-speed drive somewhat mitigate the effects of having only one stage?
- Which engines and aircraft had multi-speed drives? Which had only single speed?
- Whatever else comes to mind

The first NAPIER 'Nomad' prototype employed a CVT mechanical drive. Fairly crude one.

 

[PAT303]

He might possibly have been referring to the boost override switch.

http://www.spitfireperformance.com/spit2pnfs3.jpg
They call it the boost cut out switch here but it's the same thing.

 

[MIflyer]

I believe the P-40M was the first production aircraft to have an automatic boost control on the V-1710. Since the P-40M was built exclusively for RAF and Empire nations use, that makes sense. They were used to having the automatic boost control in the Merlin and no doubt they had far more pilots who expected the V-1710 to have one as well.

On the other, there is a statement in the book "Vees for Victory" that the RAF found it a good idea to take the automatic boost control off the V-1710 and let'er rip.

The later P-38's had an automatic boost control as well, but since the turbo already had a form of boost control it was common for the two regulators to fight one another, leading to jerky flight at times (any of y'all ever try hooking two pneumatic or electronic regulators in series?). Perhaps this was not too much of a problem with fighters but with the recon F-5's it was unacceptable. So at at least some recon P-38 units, such as the 9th Photo Recon, the automatic boost control unit was removed.