Bill, List,
Great question. There is certainly a "breathing efficiency" issue when
comparing Wankel engines to their piston kin. Although both share the same
four Otto Cycle events, (Cycle being a better term than "stroke" when
referring to a Wankel, since the action of the rotors is in only one
direction.) each cycle of the Wankel engine extends over 270 degrees of
eccentric shaft rotation vs 180 degrees crank rotation in a 4 cycle piston
engine. Comparing power strokes between two and four cycle piston engines
and Wankel engines then clearly shows the breathing disadvantage that the
Wankel is graced with. Within the commonly available engines we are also
restricted to factory displacements and compression ratios which cannot
reasonably be altered. We can alter port timing and size to increase
breathing capability, but as Dave's pointed out, 360 HP is about all that's
possible from a naturally aspirated 13B (1308cc). Best I've seen from a
carbureted 13B was 328 HP. With my slightly too small carburetor I'm hoping
to get just over 300 HP next year.
I think it may also be appropriate for us all to start referring to the
engines as Wankel engines instead of Mazda rotary engines. As Dave
demonstrated with his engine list, there are far more manufacturers than
Mazda. The term "rotary" also seems to somehow mislead people into
believing that the rotor is simply spinning inside the rotor housing. Its'
movements are far more complex than that. (...and I've actually gotten an
engineer to adopt my highly technical term... "monkey motion.") There's a
simple Java demonstration (animated model) of the engine on the same website
with the Wankel engine list if anyone wants to see how the rotor is actually
moved around the stationary gear by the eccentric shaft. On this item a
picture is truely worth a thousand words. Just look around in the "How it
works" section of the index at <www.monito.com>. Lots of educational
material there.
Chuck Rothfuss
Might snow tomorrow in
Pole Cat Hollow, NC
At 09:26 AM 12/27/2000 -0500, Ardun Bill wrote:
>Chuck, is there an issue of "breathing efficiency" at play here? I know
>that today's best four strokes and today's best two strokes are not a
>fair match based on displacement, because the two stroke, although it
>does not have as good breathing (volumetric efficiency), has a net power
>output better than the four stroke merely by virtue of double the power
>strokes.
>
>How does the rotary fit into this group, in other words, does it breathe
>better or worse than its two and four stroke piston cousins? Porting,
>time available for induction and exhaust, etc.
>
>Regards from Ardun Bill where there's a dusting of snow this morning in
>the Great Dismal Swamp, Chesapeake, VA
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