Paul and Dale,
I know this has been a source of disagreement in the past but I feel
compelled to respond to the displacement narrative.

Displacement is defined as "c: the volume displaced by a piston (as in a
pump or engine) in a single stroke.
All manufactures of rotary engines use the same method as Mazda in
determining displacement.

The only people that define the rotary displacement differently are
sanctioning bodies to help competitors that must compete against it!
This is also done to handicap the two stroke engine.

A second idea for consideration. If we physically take the 3.15" wide X
7.5" long rotor (23.625 sq in) working against a very short 5/8" stroke
we get our 653 cc. When we add the 1500 psi to the above volume we get
torque.

If we could some how magically double this displacement we would double
torque and HP.

Let me concede that there is a clue that might indicate that it's
displacement is larger... and that is the way it drives a turbine wheel
causing turbo selection to be  skewed larger than 4 strokes.

But in the end it is a very small and intriguing simple engine with a
very high heat load unencumbered by parasitic valve mechanisms.

My Take,
Barry Bordes


The rotary is not a two stroke. It is a four stroke.

Lets turn it around. How much air would a 2.6 liter two cylinder
TWO STROKE engine pump in one revolution?

As far as HP is concerned the ONLY thing that matters is how much
air a four stroke engine pumps in ONE REVOLUTION at 100% VE.
Not the physical displacement of x number of chambers.

The definition of displacement, as far as engines are concerned,
is only valid in context with the type of stroke.

Here is what Ansdale has to say about that.

13B rotaries are raced in the 2.6 liter class world wide
for a good reason. The only reason they generate more power
than a 2.6 liter four cylinder engine is they turn faster
and breath better. Lately that is less true as the piston
engine RPM has been raised by detail development and the
use of high strength to weight ratio materials like titanium.
Also four valves per cylinder has improved the breathing.
It is very rare for any 2 valve cylinder to have a VE over one.
The RX8 engine is just over one and P-ports are typically
1.2.

Formula One (2.5 liter as I recall) V8 engines were
turning 19,000 RPM. At least four valves per cylinder with
a very short stroke so larger valves can be used for a given
physical cylinder displacement. You will not find the details
of a competitive Formula One engine anywhere. Its a well
kept secret. However I would not be surprised if the VE's were
well over one. Applying the RPM difference to a 2.6L p-port rotary
making 340 HP at 10,000 RPM would make the Formula One engine
about 19,000/10,000 times 300 HP or 655 HP which is about
right for a Formula One engine in that period.

Paul Lamar


Paul,

It probably would be more correct to call a rotary a two sweep engine
with 4 phases: intake, compression, power, and exhaust.
As you know there is no reciprocating type stroke involved.

The only comparison to the 2 stroke that I used was that it is also
handicapped by sanctioning bodies because of its performance over a 4
stroke.

Did outlawing the peripheral port change its displacement?... no only
its competitiveness.  That after the rotary was penalized by giving the
4 strokes a double displacement advantage.
This does make sense to keep other manufactures competitive, profitable
and happy.  But it doesn't change the definition of displacement.

The cutaway picture of the rotary that you showed in Blue is exactly the
depiction of its displacement.  Displacement is not denoted by Ansdale's
opinion... it is a dimensionally exact measurement.

Our little engines are indeed more powerful than most can envision.
Barry Bordes


The Ansdale definition of Wankel displacement is accepted by all the
world's engine engineers..
It is not an opinion. It is based on facts.
That's it period :-) You need to get his book and read it.

Paul Lamar

Barry, I have a question. Why do you state rotor dimensions in imperial
units and then state displacement in metric? All Mazda and I would
suspect almost all manufacturers use the metric system. Ingersoll Rand
may have used Imperial due to American design and the dimensions involved.

Dale Davies


Paul and Dale,
Here is a list of Rotary engines produced.

https://web.archive.org/web/20050219094802/http://www.monito.com/wankel/engines.html <https://web.archive.org/web/20050219094802/http://www.monito.com/wankel/engines.html>

The displacement figures stated represent what?  Are we to guess that they are 1/2 or doubled or actual?
This is the problem with not using a standard for displacement.  You guys want to use a different standard... this introduces confusion.
I would ask that you show one manufacturer that uses Ansdale's method as its standard.

As for metric vs imperial units I tend to use either depending on the majority audience.
Respectfully,
Barry Bordes


People have no trouble understanding that 2 cycle engines are twice as powerful as a 4 stroke.
However the Wankel is not a 2 stroke.  There in lies the problem.

Just call them rotor dimensions. Or Wankel displacements so people that are not familiar
with Wankel engines can form an equivalent to a 4 stroke piston engine in their minds.

BTW if you have Windows with Office please load HTML's in Word and save them as a pdf's and
send that to me. HTML files do not forward well to all operating systems.

Paul Lamar

Barry,
As I stated previously, many markets tax automobiles based on engine displacement. Standard thinking defines that calculation on each cylinder firing once. The problem and controversy regarding Rotary or Wankel engines comes about in the fact of being four stroke cycle engines. This is an established and accepted fact.


A four stroke cycle four cylinder engine requires two complete revolutions to enable all cylinders to fire once each. Therefore to compare engines on a more level playing field you need to use two complete revolutions of the e-shaft for displacement calculations. This is what virtually all competition sanctioning bodies use. Some have used three in deference to each rotor face experiencing a combustion event.

Modern recip engines using stronger lighter materials have brought power per liter into the same level as the rotaries and operating RPM limits have increased. Variable valve timing and lift capability with electronic controls has also contributed to broader and extended torque and power bands.

As to your engine and displacement list shows, all displacements were listed in cc's. As I described possible engine dimensions I used the metric system for eccentricity, radius and width. Using one system makes it easier to understand what is being depicted. Using the same as everyone else puts us all on the same page which can help with understanding and comprehension. This especially applies to people new to this that are still trying to get a handle on the operation of the rotary engine.

As a note; power boat racers factored rotaries at 1.8 times manufacturer (Mazda) stated displacement. I reference Mazda as the only manufacturer of rotary engines in sognificant volumes. In these boats a turbocharged four rotor could compete quite well against the turbine powered boats. The turbine racers keep their power down a bit to get the used helicopter engines to last longer. Overhaul costs is what dictates this.

Dale Davies


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