Hi
  Do you have a HP / RPM graph for a 13B engine.

  Paul M

  Stock side port or or P-port?

  Here is an early 13B of around 1989 and some others.
  Note the 800 HP drag engine is running on Alcohol
  and can drive a 2000 pound car to 153 MPH in the
  quarter in less than 8.66 seconds.
  The engine is VERY ROBUST. That is about 4 HP
  per pound of engine weight.

  Paul Lamar

 Paul,
 Looking at your Mazdatrix dyno, the power drops off considerably as
 the RPM drops from the 7000 range to 5000. 5000 would be a bit low
 for cruise but even 6000 is down a lot. What do you attribute the
 drop to; intake length, exhaust tuning? Boing Boing engines can have
 a dip when cam, heads and manifolding do not match up.

 Dale Davies

 This is what you will get with a highly

 tuned engine.
 The RX8 has a very complicated intake system to tune
 the engine over a wide RPM band. You don't need it in
 an aircraft engine. Cruise at the 6000 RPM torque peak
 for lowest BSFC.

 6000 RPM is the sweet spot in a Mazda engine as that is where
 the bearing loads are lowest.

 Lets say one is real cheap and one wants it all including max power
 on the top end. One has a constant speed prop and wants to run the
 engine at only 4000 RPM and fly the airplane in the bottom of the
 drag bucket around 140 MPH to maximize the MPG.

 Then implement this.

 I think Cary built an engine like this but I lost the pictures.
 Cary can you send those pictures again?

 Paul Lamar


Hi Paul,

That is what I was getting at. If you want to cruise at 6000 RPM, would you
not
want to tune it for a torque peak at that RPM? Fuel efficiency should be
better that way. Your dyno sheet shows about 140ft/lbs at 6000RPM. Or was
that
with an intake more suited for access on the dyno?

Dale Davies

Which dyno sheet? I sent a lot of them.

This is the p-port engine I am advocating.
about 195 foot pounds at 6000 and 250 HP
at 7500 RPM.

Yes that is exactly what we did with the P-port.
The best BSFC is always at the torque peak.

That is not necessarily the best MPG however.
That usually happens down in the drag bucket.

Paul Lamar


Who cruises at best drag speed??  (Except for long range record setters).  ;)

How about Carson's Speed?  It's the fastest an airplane can go for the
least incremental increase in fuel flow.  It works out to be around
1.32 * Vg  (L/D - best glide).

http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm

The implication is that fuel efficiency is important even if not
flying at best L/D speed.

None the less, wouldn't it make sense that if the power setting which
gave the "best cruise speed" also coincided with a torque peak.  Seems
like the torque peak would happen where the pumping losses and drag
loads were minimized.  Ideally, an engine would behave like it's BIG
while in takeoff and climb, and "smaller" while in cruise.

I still think the trombone intake is pretty elegant.


Matt-

That is when the trombone comes into play.

John Pun Dinkel will love it :)

Paul Lamar