Ken Powell wrote:

     Paul,
     I believe that you may be underestimating NA horsepower slightly in
     side port engines. 

Yes I think you are right. I might need to bump up that rule of thumb to 190 HP
at 6000 RPM.

     Tracy is burning over 17 gph (his gauge goes no
     higher) which equals approximately 189 HP if we assume a bsfc of 0.54
     at WOT.  I believe that Tracy's engine uses 4-port Turbo end housings
     and rotor housings but rotors from a 1989 or later NA engine (9.7
     compression ratio) and that it has been 'street ported'.  Note that
     this is with a tuned intake but not a tuned exhaust.  There is still a
     little more performance locked in that engine if anyone can figure out
     how to get a tuned exhaust in a RV-4 cowl.  Also, I suspect that
     Tracy's intake is tuned for 'cruise', not top speed.  So a engine
     'tuned' for 6500 RPM could be expected to put out more HP due to
     efficient intake and exhaust systems.  I would like to try intake
     runners 20" long and exhaust pipe lengths of 31".  Tracy's RV-4
     doesn't have gear leg / wheel pant intersection fairings and he says
     that he has been too busy to 'tweek' the aerodynamics.  Even so, his
     performance is equal to a 180 HP Lycoming. I understand that his top
     speed is 207 MPH at 6300 RPM.  I did not ask at what altitude that he
     achieved these numbers.  On the other hand, the Lycomings may be
     generating more than 180 HP themselves based on the RPM they are being
     run at (in Van's quoted performance I don't remember the RPM).

     Also, do you think that Tracy's 68" wooden prop is starting to get
     inefficient at 207 MPH and 2900 prop RPM?  This issue may force us to
     get our HP at less RPM due to 2.17 reduction ratios or to build our
     own props per your discussion for the constant speed prop project.

     Ken Powell

I have been trying to talk him into running the Sun 100. He could make
a salary of $800 per hour :-) I think a carbon fiber prop would help.
Everybody that have gone with Klaus'e props (LSE) have great things to say
about them. Some are engineers and have calculated about a 5% efficiency
improvement over a wood prop.
 
Paul Lamar
 
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