Paul;

    I have been considering building a FEW (Fighter Escort Wings) TF-51
http://fighterescortwings.com/html/few_performance_data_ver3.html . They
typically use a 350 V8 Chevy engine, however, I was thinking of using a
4-rotor rotary engine. This airplane uses 500 HP and prop, PSRU, and engine
weigh between 600 to 700 LBS. I am not sure if it would be better for me to
use a 4 rotor engine and if I did which one would be best or if I should use
a 3 rotor 20B. I am thinking of running a higher HP engine at lower RPM and
possibly negating the need for a PSRU. The airplane has a 340 MPH VNE and
they show that it will use a 350 to 500 HP engine. My primary motivation is
to have a safe reliable airplane, not a fast dangerous airplane.
    I respect your experience and knowledge and am very interested in your
recommendations.

Sincerely,
Mark

Well I don't think you will get the HP you need out of a direct
drive four rotor as you will need a large prop. RPM does not
hurt rotaries likes it hurts piston engines. A rotary is happiest
around 6000 RPM.

You will probably have to build your own PSRU. Take a look
at the Allison auto transmission that GM uses in some of their heavy
duty trucks.

Paul Lamar