marc wiese wrote:

"THE PISTON ENGINE GOES BOING, BOING.boing, boing, boing-but the Mazda goes
hmmmmm." Remember Mazda's admittedly cornball 1970s' TV ad? Complete with a
kid on a pogo stick embodying the evils of pure reciprocating movement, the
spot touted the smoothness of this novel powerplant melds the Otto cycle's
events of intake, compression, power and exhaust with rotaring motion. Like
the Porsche 911's air-cooled flat-6 or Saab's Wankel will be forever as it
has twirled beneath the hoods of RX-3s, three generation of RX-7s and even,
for the Japanese market, a 26- passenger bus called the Parkway Rotary-for
more than three decades.

Yet the concept was dreamed up quite literally - in the summer of 1919 by a
17- year-old German boy. Felix Wankel. In his dream, Wankel drove a car of
his own construction to a concert, where he even remembered boasting to his
friends, "My car has a new type of engine: a half-turbine, half-reciprocating
engine. I invented it!" Wankel succeeded in turning his vision into hard
prototypes, at first with the German government and later with NSU, which
first built a Wankcl-iype supercharger that enabled its 50-cc motorcycle to
set a world speed record of 122.7 mph in the mid-1950s. NSU ultimately
focused on four wheels, building a single-rotor 2-seat roadster called the
Wankel Spider in 1963, followed by the homely Ro 80 2-rotor sedan of 1967.

Both GM and Mercedes-Benz took long, hard looks at the rotary's viability.
But it was Mazda, largely through the engineering brilliance of Kenichi
Yamamoto, that refined the design and made the rotary engine a reliable,
mass-produced reality. Since the Japanese introduction of the Mazda Cosmo
Sport roadster in 1967, Mazda worldwide has sold more than 1 .8 million
rotary-powered cars, trucks   and the occasional bus. Sadly, the last
U.S-market RX-7 blinked its taillights goodbye in 1996. Why did that sports
car, practically deified by the automotive press including Road & Track. go
away? Partly because of the overall softness of the sports-car market, and
partly, according to Philip R. Martens, Mazda's managing director, because it
just didn't make business sense to meet stringent U.S. pollution laws. "We
could have made it comply with emissions, but the costs of the catalytic
converter and some of the other things were just too high," says Martens,
whose daily driver around Hiroshima is the latest twin-turbo 280-bhp RX-7
variant, still sold in Japan. Enter the new Renesis rotary, a 2-rotor Wankel
capable of similar output without turbos and having, more importantly, a
clean bill of U.S. emissions health "into the foreseeable future, which to me
is 10 years plus," says Martens. Showcased in the new RX-8 (see "Sports Car
Tsunami," March 2001), the Renesis is the anchor point for a whole family of
engines. "The essence of the program was not to develop an engine tailored
for one car; I believe there's enough bandwidth in the sports segment for
more signature products along that range," Martens said. Key to the design is
moving the exhaust port from the periphery of the rotor's trochoid-shaped
housing (picture a cocoon, or a fat peanut shell) to the side plates, where
the intake ports also reside. Not only does this design eliminate port
overlap, the two side exhaust ports per chamber offer nearly twice the area
of the single peripheral port for greater power.

And where unburned hydrocarbons used to have an easy escape path out the
exhaust, the Renesis' side-port design corrals them against the trailing apex
seal, below the port; they're then carried through to the next combustion
cycle, lowering emissions. A double-walled exhaust manifold plus the absence
of turbochargers also means less heat loss before the 2-stage converter,
critical to emissions at start-up when an engine is at its dirtiest. "Our
research center has spent a tremendous amount of time working on the
catalytic treatment," says Martens, "to make sure we don't choke the exhaust,
which is key to the free-revving performance we want." Free-revving indeed;
the rotors are a fill 14 percent lighter than their earlier counterparts,
enabling a 10,000-rpm redline that takes bragging rights away from the Honda
S2000's 9000-rpm zenith. (It should be noted that each revolution of the
rotor translates to three revolutions of the eccentric shaft, the rotary's
equivalent of a crankshaft.) There are numerous other smaller changes-an
elaborately baffled oil sump whose ultra-slender 1.6-in, depth allows the
engine to be set lower in the car; injectors that more finely atomize the
fuel; a triple-path induction system that takes full advantage of the
resonance "supercharging" effect; and an advanced engine- management system
that's said not to use oxygen sensors at all.

If a chink exists in the Renesis' armor, it's in torque production-in current
tune, it generates 153 lb-ft. at 7500 rpm. Curiously, those numbers are
identical to the 52000's, and that car has been criticized for lack of
low-end grunt. But Martens stresses that it's how the torque is distributed
and how it's matched to the car's yet-to-be finalized gearing-that will
ultimately impact the RX-8 's fun-to-drive quotient.
"We want to have the feeling of, 'Oh my god, 1 didn't know this would do that
in this range,'" he said. "Flat torque curves are great, but what we really
want is a lively car. It has to have a unique identity when you get in and
drive it." We anxiously await the production version.


· The new Renesis rotary is slightly more compact than the Twinturbo 2-rotor
it replaces, and lighter: Rotors have been pared from 9.5 lb. to 9.2. and
targeted overall engine weight Including all accessories is 12 percent
less-from 344 lb. to 303. Yet it's the side exhaust ports  that make the
rotary an emissions-friendly engine


CURRENT PERIPHERAL EXHAUST


Port configuratian is the key. Old-style peripheral exhaust ports offered
unburned hydrocarbons a relatively easy path to the exhaust system. New side
ports, which exit laterally, parallel to the rotor's axis of rotation, help
to trap the unburned gases and carry them through to the next combustion
cycle. A desirable byproduct of the new ports is what's said to be a lower,
clearer-sounding exhaust note, perhaps ending those unflattering comparisons
to outboard motors and chainsaws.

 
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