This is what I have come up with so far.
    The GT40 looks like the replacement for the TO4.
    It is about the same size. It meets Dave Leonard's
    suggestion for using a large turbo loafing along.

    We start with the airflow requirements of the rotary at 15 psi boost.
    That should give us around 400 HP with side intake ports and a VE of
    around 100% (no intake valves). My guess is that would be about 480 HP
    with p-ports that have a higher VE. At sea level of course.

    The airflow for a side port rotary is about 35 pounds per minute.
    In the  compressor chart that puts us near the middle of the 78%
    efficiency island using the larger diameter 88 mm compressor option.

    That's good as it will load down the turbine a bit and tend to
    keep the turbo charger RPM down. I choose the 1.34 A/R in the
    turbine chart for the same reasons. More about A/R shortly.

    If we limit the boost to about 9 psi boost for cruising (flat rating)
    we should still be on the island.

    What do you think Dave Leonard?

    Paul Lamar ...No rotor no motor.


That looks good to me Paul.  Looking at the compressor map i like the 50
trim the best.  That is because a 13B will have relatively small airflow
compared to the larger displacement engines these turbos were designed for
an the 50 trim is shifted slightly to the left. (I think 100% VE is a little
optimistic unless you have a well-tested and refined intake manifold...
which none of us have). But more importantly, the 50 trim maintains
efficiency  as the pressure  ratio climbs which is important in aircraft.
There are no RPM numbers on the compressor map, but they look about right
assuming the RPM is not that much different from other turbos ( i.e. you
will not be operating in the upper regions of the map).