>> 1) The pumps could
> > have differing efficiencies. That's possible but it doesn't
> > explain the magnitude nor why auto manufacturers would persist
> > with an inferior pump design if reverse engineering a Davies
> > Craig pump could yield such superior results.

How long did it take American manufacturers to wake up to the fact that the oriental's were eating their lunch?  Why would they change out a part that has worked reliably for 100yrs and replace it with something that will provide very little benefits.  Remember most auto engines rarely rev up to 6000rpm, and never for long.  The rotary is notable in that it does rev higher than most, but even then it doesn't stay at those high revs.  It's even more notable in an airplane, as it tends to rev high and stay there.