This discussion of displacement has been the most
amusing thing I've seen in a long time.  ;)

Each rotor rotates at 1/3 of e-shaft speed.  Since the
rotor has 3 sides, each rotor has one intake "stroke"
per e-shaft revolution.  Swept volume of one face of a
13B rotor is 650cc.  Thus 1.3 L of air are ingested
(assuming a VE of 1.0, which I believe we have all
been doing for the sake of argument) per e-shaft
revolution.  This is likely where the 1.3 L
designation comes from.

Since a 4-cylinder 4-stroke engine takes two
crankshaft revolutions to fully cycle all four
cylinders, to ingest the same amount of air per crank
revolution, the 4-cylinder 4-stroke engine would have
to displace 2.6 L.  This is why we see the
double-displacement equivalence rule in many racing
classes.  Unless you p-port, you're probably getting
fairly similar VE as you'd find on a fairly large
number of 4-stroke 4-cylinder car engines.  Since as
was noted in another thread here that the amount of
available oxygen is your limiting factor, the
equivalence rule makes a lot of sense.

The main advantage, IMHO, of a non p-port rotary is
the fact that it has a lot more time to complete
combustion for a given "crank" speed than a 4-stroke
engine.  Unfortunately, the shape of the combustion
chamber is far from optimal for combustion efficiency.
A modern pent-roof combustion chamber with a lot of
squish area does a far better job in terms of
combustion efficiency and thus nets more power and
lower BSFC, all other things being equal.  Rotaries
have an additional advantage in not having to handle
the sorts of inertial loads found in a piston engine
from starting and stopping the piston's mass over and
over again, and with no valves to float, they can rev
higher than comparable displacement piston engines
usually can.

I am not entirely sure why the discussion of
displacement got so entangled.  It's pretty basic...
Almost as basic as knowing when Mazda first built a
production turbocharged rotary.  ;)

Adam Wade

Very good Adam I see nothing wrong with your explanation.

Except about the 12A turbo :) I am still not convinced.
I am still waiting for our resident expert John Dinkel
to comment on that. No mention of it in my Yamaguchi RX7 book.

Paul Lamar ...No rotor no motor.

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