All this talk of over spinning turbos keeps me coming back to high speed
alternators.

Monty & I discussed the topic at the Rotary Fly-in a couple years ago.
My impression was that there were off-the-shelf high-speed alternators
available that could be used in a turbo compound fashion.  (Monty,
please feel free to correct me if I'm off base here ...)

If the exhaust side of the turbo is driving an alternator, it would be
relatively easy to control turbo RPM by varying alternator loads.

The load might even be a high-efficiency motor (rare-earth magnet type)
driving the e-shaft.  That certainly would eliminate many turbo compound
coupling issues, like fluid couplings, gear lash, linear gear tooth
speed limitations, etc.

Paul's argument was that there would be too many losses in the system.
There would be some to be sure, as with any system - mechanical or
electrical.  Also, unless the alternator/motor combination used high(er)
voltages, there would be some heavy cable requirements to transmit the
power.  Assuming 20 HP to be recovered and no losses:
    1 HP = 746 W
    20 HP = 14,920 W
    14,920 W = 124 Amps @ 120V
    14,920 W = 62 Amps @ 240V
    14,920 W = 31 Amps @ 480V
FYI:    Convert Horse Power to AMPS:
    HORSEPOWER= (V x A x EFF)÷746
    EFFICIENCY= (746 x HP)÷(V x A)

The questions of this thread should center around:

- Are high speed (50-80K RPM) alternators available OTS?
- Can they be safely coupled to the turbo?  Possibly replacing the
compressor section?  (U-joints are out!)
- Are high efficiency electric motors available OTS that can be bolted
to the e-shaft?
- Can this be done to recover some exhaust energy, or is this a waste of
time?

Point of interest:
I like the turbo as a muffler.  If I can extract energy too, that would
be a bonus.  Otherwise I'll probably stick with the low-tech
muffler.  :)