"Yes, the RO80 and the RX8 can not be compared directly due to the
different ports and different aims. But then, one would expect
improvements over time and Mazda had more money to spent. As build then,
the two were not that far apart in top hp per displacement."

Yes but it is still apples and oranges. NSU did not have to put
up with draconian smog rules so a p-port was viable. A p-port is
not viable on the RX8 street engine for smog reasons
alone although I have an idea that might make it work :)
P-ports on a 13B are worth 50 HP at 7500 RPM and almost
100 HP at the RX8 red line of 8500 RPM on a 13B. I would say
only 60 HP over an RX8 engine. Lots and lots more over whatever
Mazda gets out of a 16B.

The largest problem with the Wankel engine is the combustion
chamber surface to volume ratio as far as thermal eff.
is concerned. Read BSFC. Much heat is lost to the cooling
system. This is bad for eff. but good in terms of pumped up
turbo charged power per cubic inch. The rotary will run at levels
that would melt a piston engine. 400 HP per rotor is common
and Abel Ibarra is working on 500 HP per 13B rotor.

A sphere is  perfect combustion chamber with the spark
plug located in the center. Max volume minimum surface area.

A round distorted short cylinder shaped combustion chamber is
next and is the norm in piston engines.

A short square box is next. Much like the AIXRO go cart
Wankel and the Norton Wankel to a lesser extent.
both of these engine are handicapped by either charge
cooling or air cooled rotors. The cooling blower is
consuming engine power in the Norton case.

The next best is the Mazda 16B rectangular box approaching
a square.

Next in line is the Mazda RX8 and 13B.

Perhaps the NSU RO80 engine and the Mazda 12A engine compete
for last place in the Wankel world combustion chamber competition :)

Paul Lamar

Well, likely so.
For one thing, agreeing with you, using the same geometry of E and R and
increasing the width does reduce the surface area in relation to the
volume.
Both, the volume and the piston area go up linearly with the width,
while the side areas, those of the two end walls, stay the same making
the overall relative increase of the surface area less than the relative
increase in volume.
Changing the ratio of E and R, as far as I know, a smaller E and larger
R, where the product of the two is kept the same for same displacement,
will increase the surface area and also increase overall housing
dimensions, and the maximum possible compression ratio goes up as well.
The 'narrowing-in' of the small axis is less pronounced.

Regarding your last mentioned group and even more so the experimental
EA871 engine, having a lower R/E ratio was good but the narrow piston
was counter productive.

I see that the AIXRO also goes the route of a very wide rotor. Compared
to the RX8, the width is more like 105 mm.
Although AIXRO is a small engine. I don't know their consumption figures.
I can't wait to see if the fuel consumption goes up or down with the
16B. Likely it will go down with unchanged R/E ratio which is what you
expect as well.

As to your statement: "The rotary will run at levels that would melt a
piston engine. 400 HP per rotor is common and Abel Ibarra is working on
500 HP per 13B rotor".

That is because the rotor is iron based material not aluminum.
If one would build a reciprocating piston engine where the piston stroke
is only 1/3 of the piston diameter, using a cast iron piston and a
crankshaft similar to that of the Wankel, where the large bore of the
connecting rod circumscribes a strong shaft, similar hp ratings can be
achieved durably.
500 hp per 1.3 liter displacement is 385 hp/litre. That is about the
same as F1 engines get. I believe their pistons are Titanium, at least
their connecting rods are.

However, the F1 engines do it at a very high rpm, as they are not
charged, and life of a F1 engine is very short, measured in 1 or 2 deka
hours or less.
The Wankel operates at lower rpm but with charging to get similar
results. The above described RPE likely could do that too.

Rolf



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