If I were Mazda I would not build a bigger rotary.
That is not going to buy them 20% better MPG.

If not building a 20% higher MPG turbo compound rotary I would focus
an a computer controlled manual transmission that shifted
super fast upon kick down to exactly the right gear
for the current speed such as this transmission from Mercedes.

They can also increase the power on the top end
with a trap door p-port and still meet all emission
regulations.

Paul Lamar

Hi Paul,
I agree with all of your ideas on efficiency increase, the turbo
compounding and especially the MB type transmission.
Why would a trapdoor type PP be any better than a throttle in the PP
induction tract that only opens at high rpm;
I cannot see the reason for such complication in the trapdoor design,
when it really is only a pop open throttle after all.
BR, Dave McC

The trap door, when closed, eliminates the induction track to exhaust
track gas flow path. This gas flow from exhaust to intake at low RPM causes
misfiring which puts out a dollop of unburned HC. That is why Mazda went to
side exhaust ports on the RX8 engine. It is all about emissions at low
RPM's low power. When the drap door is closed the engine operates EXCATLY
like a current RX8 engine.

-- 
Paul Lamar ...No rotor no motor.

Paul,
Are you saying that the trap door introduces the inlet charge later. So much
later that the exhaust port is closed. Some exhaust will still travel up the
rotor compression at low RPM, but you wouldn't get new charge in the exhaust
at high RPM or would you. I'm confused at how it ( trap-door) would work
beneficially.
I thought the RX8 inlet and exit was designed for no overlap for Hydrogen
use. Reciprocating valve engine can't do that, I'm led to believe.
George ( down under)

No.

The trap door is closed up to 6000 RPM. The EPA never checks
or cares what the emissions are at over 3000 or 4000 RPM. Max speed is 50 MPH
and it takes 20 seconds to go from 15 MPH to 50 MPH so the
engine is not working very hard at all. See the attached EPA driving cycle.

You were misled. It all has to do with emissions running on gasoline
at low power and RPM levels.

Don't hold your breath on hydrogen use. There is no infrastructure
for hydrogen use in the foreseeable future as nobody in this country
wants to build nuclear power plants. Not only that power is down by half and
range is only 25% of what it is now. Not a practical option.