Hi Paul,
 Here I go with that thinking stuff again.:-)) If you were doing
a turbo  compound system on your RX8, would you also change the
rear axle  ratio to something taller? On a car the higher gear
ratio would put  more load on the engine to maintain cruise speed,
resulting in the  throttle being more open. That reduces pumping
losses and more hot  air to apply force on the turbine. That
should then add slightly  more advantage from the turbo compound
system. With that in mind,   what gear would you chose instead of
the 4.44:1 they have?

Dale Davies
 Lets assume the car has a frontal area of 20 square feet.
The rule of thumb is 80% of the height times the width estimates
the frontal area. Lets say 6 feet wide and 4 feet high.
Or 5.5 feet wide and 4.4 feet high.
 Lets also assume the C sub d of .3! Typical for a Prius. Drag would
then be 20 x .3 x 75 x 75 x .0026 or 88 pounds at 75 MPH. 75 MPH
is  110 FPS. So required HP is then drag x FPS or 8250 pound foot per
second or 15 HP. Double that for tire rolling resistance and you
get  30 HP needed to maintain 75 MPH on a level road at sea level.
 Automotive turbo compound is a real challenge. 90% of the time a
car  cruises on the freeway or autobahn at 30 HP while the engine
may be  rated at 400 HP. In order to make that highly efficient
you need a  small engine running at about 75% of it's max power at
best torque  RPM. This is the rational for shutting of some of the
cylinders in a  piston engine.
 The rear axle ratio could be the same as the current RX8 at around
3.5:1 for acceleration and hill climbing reasons.
 What would be great is a 2.5 rotor Wankel engine. In other words
2  rotors for acceleration and hill climbing and a smaller one
rotor  for cruise. The unique configuration of the e-shaft makes
that possible.
 http://www.rotaryeng.net/RX8-TC-eng3.html
 The small one rotor engine would have a tiny turbine to get the
BSFC below .36! Diesel range or below.  The fuel burn would then
be  about 10.8 pounds per hour or about 1.7 gallons an hour. At 75
MPH  the MPG would then be about 44 MPG.
 The advantage over a hybrid is less extra weight and cost for
electric motor and battery. Not to mention the limited availability
of lithium. The advantage over the diesel is better acceleration
and  less cost and weight. No carcinogenic black smoke problems either.
 Paul Lamar

Ok. How would you propose to couple and decouple the "main" engine when
needed? The trick will be to do it seamlessly. With cylinder
deactivation and drive by wire this is fairly simple. When engaging
a whole other engine would be difficult. The rotary has low
rotational braking forces. It would likely be easier to build a 3
rotor with one rotor being 50 or 60mm wide for full time use. The
advantage would be that current machining equipment can be used.
Then the cut rotors need lube while reducing air intake to reduce
pumping loses. An R100 size rotor should be around 125HP with
Renesis end housings. If narrowed to 40 or 50mm the power would be
reduced and a larger throttle position required.

I welcome your thoughts,

Dale Davies

One way clutch. AKA  Sprag clutch.

Paul Lamar

This makes me wonder ... why hasn't Mazda already done this if it is
that obvious?????  They could make a 50 MPG Mazda 6.

SD

Me too. Back in the late 1940's, 1950's and 1960's over 9000 turbo compound
aircraft engines were built. They reached a TBO of 3000 hours in
airline service.

As far as  turbo compound piston engines are concerned they  are
very hard on exhaust valves and much energy is therefore lost in the
exhaust valves. Needless to say the rotary has no exhaust valves so
in theory it would be significantly more efficient.

Paul Lamar

What engines were turbo compounded in 1940-60's.

Van Vannoy

Allison, CW R3350, Napier Nomad. P&W did some TC R&D for the B36 R4360.

Paul Lamar



Does any of the Reno racers running in the warbird class, use a TC engine?

Dale Davies

Rare Bear uses the extra robust crankcase but not the turbines.

Paul Lamar