Paul,

 I realize that the intake and exhaust tubing diameter and lengths
 will affect the torque (thus HP) curves. What would you attribute
 the dip in the curves between 5000 and 6000 RPM? I also realize this
 is only one dyno run.

 I would expect economy cruise prop RPM between 2000 and 2100 RPM
 which would be about 5600 to 6000 RPM engine. With that in mind, a
 change in tuning of the intake and exhaust would seem to be indicated.

 Dale Davies

 There is a thing called "Q" The higher the Q the purer the tone
 and the greater the effect. That narrows the torque peak.
 It also generates dips in torque over the RPM range. We don't really
 care what happens below 6000 RPM as that is an ideal cruise RPM
 where the loads on the rotor bearings are lowest. It is also a low
 point on the BSFC curve or fuel burn.

 I am not sure how to change that. Perhaps the 180 degree bends in the
 tube is already doing it because our results are broader than
 the Le Manns engine and we are getting slightly less HP.

 Here is the results Mazda got for the Le Manns engine. We tried
 to copy that as closely as possible based on the gear box ratio
 we had to work with.
 http://www.rotaryeng.net/fund-of-intake.html
 http://www.rotaryeng.net/Mazda_R26B_US.pdf

 Paul Lamar

 Hi Paul,

 After reading your reply, I make note.

 In the Fundamentals of Intake Design you state "with a CS prop ...
 slow the
 engine to 4500RPM to 5000RPM reducing engine friction and improving
 BSFC."

 On the dyno charts for the 13B p-port;
 with 24.5" intake runners, about 225HP at 6000RPM and 190HP at 5500RPM.
 with 28.0" intake runners, about 225HP at 6000RPM and 210HP at 5500RPM.

 At 6000RPM the prop is rotating at 2105RPM. At 5500RPM the prop is
 rotating at
 1930RPM.

 At 5500RPM the prop is turning slower in the air and should have less
 drag
 thus more efficient. With the longer intake you also have about 20
 more HP
 available, which should increase the air speed a bit.

 Reducing the RPM from the 6000RPM which is the least bearing load to
 5500RPM
 will not change the bearing loads drastically. It should help the
 fuel burn
 some though.

 After reading the Mistral information a while ago, they were stating
 a cruise
 at 2000RPM prop for economy. Their intake is also long which suggests
 a tune
 for lower RPM.

 Now the dyno of the Renesis with 19" intake would look different with
 longer
 intake runners. The side exhaust will affect the tune also. It may
 provide a
 better BSFC with the right exhaust and intake tuning due to less
 fresh air and
 fuel going out the exhaust: less overlap. A bit of exhaust may be
 carried into
 the intake charge which will act like an EGR and slightly improve
 detonation
 resistance.

 Dale Davies


 The Le Mmans P-port engine had the lowest BSFC of any rotary
 ever built by anyone including all the side port configurations.
 Pumping losses
 are lower with p-ports and pumping loses are a significant factor in
 BSFC.

 I'll have to go over that article and correct any errors.
 You might note Tracy has changed the common PSRU ratio
 from 2.17:1 to 2.85:1. The Mistral ratio was 2.8:1 as I recall.
 Engine friction is a minor effect in the rotary. Engine
 friction is lower than a piston engine.
 Here are a few numbers on that.

 Paul Lamar



 Just bought the race exhaust template from racing beat. Regarding
 pumping losses, is porting the exhaust worth much effort? Somewhat
 concerned about intake/exhaust overlap and perhaps much higher rpm
 needed for useful power. Any suggestions?

 Lewis.

 Porting the exhaust for an an aircraft engine running at less than 7500
 does not help much. I would not bother.

 Once you get above 4500 to 5000 overlap is not a problem.
 The engine starts to operate like a turbine. If you think about
 it a turbine engine has 100% overlap. Air has inertia so once
 it gets going in a particular direction it wants to keep
 going in that direction. The RX8 engine is all about overlap
 for idle smoothness and emission at less than 3000 RPM.


 Paul Lamar

That makes sense.  Thanks.

Lewis.