Introduction
This year is the 40th anniversary of the world’s first
production Wankel rotary engine car, NSU Spyder. Unlike what Dr.
Wankel thought then, the rotary revolution did not happen. Worse
still is that since Mazda RX-7 died last August (2002), the
world no longer has any rotary-engined cars on sale. For many
years, rotary engine was regarded as a dying breed of engines,
blame to its heavy fuel consumption and poor emission which
failed to comply with the latest regulations. At one stage,
Mazda seemed to give up the development of its rotary engine and
RX-7. However, in the 1999 Tokyo Motor Show, Mazda suddenly
announced a new rotary concept car called RX EVOLV - which
eventually becomes the production RX-8 - with a breakthrough in
rotary technology. Calling RENESIS (stands for Rotary Engine
Genesis), the new rotary engine adopts several new ideas to
reduce fuel consumption and clean up emission. It complies with
the tough Euro IV emission standard, ensuring a bright future
for the rotary engine. RX-8 can therefore be sold worldwide,
from Japan, USA to Europe.
The Chassis
In
my opinion, RX-8 is perhaps the most interesting new car in
2003, because it is so different from other cars. It might not
be Pininfarina-beautiful, but I do love its unique shape. Not
only look like no other cars, it doesn’t have any resemblance to
RX-7 too, with the exclusion of the wrap-around rear glass.
Inside, the RX-8 also gives you plenty of reasons to purchase
it. Unlike Mazda 6, the dashboard and console is stylish and has
a quality feel. The sports bucket seats look superb and feel
just as good.
Now you can see the biggest difference between RX-8 and RX-7 and
why the former is not a direct successor to the latter - RX-8 is
a genuine 4-seater coupe instead of a 2-seater or 2+2 sports
car. It also has a pair of tiny rear doors which is rear-hinged
(so-called "suicide doors"). With the rear doors and lack of
B-pillar, people can get into the rear seats easily. At the
back, there is sufficient room for average-size adults, although
a 6-footer will find space confined if he sit behind another
6-footer.
To
compensate for the lack of B-pillars, RX-8 uses a backbone-type
monocoque chassis which has a strong transmission tunnel to
reinforce the chassis. In fact, it is twice as stiff as RX-7 in
torsional rigidity, believe or not!
Not just that, the 4-seater also balances better than RX-7. By
redesigning the oil pan under the engine, the new Wankel engine
sits 4cm lower than RX-7’s to lower center of gravity. The whole
unit is located 14cm behind front axle, no wonder front-to-rear
weight distribution is a perfect 50:50. At the rear, Mazda
deleted the spare wheel and install the fuel tank under the rear
seats so that now both the engine and the fuel tank are located
within the wheelbase. In other words, it achieves a polar moment
of inertia 5% lower than that of the RX-7.
Low
center of gravity, low polar moment of inertia and perfect
weight distribution are what all sports car engineers dream for,
but not many cars can achieve them. For example, Nissan 350Z
with its big V6 engine achieves only 53:47 and a much higher
polar moment of inertia because a portion of its V6 hangs over
the front axle. Benefited by the weight and size advantage of
Wankel engine, Mazda RX-8 can easily beat its opposition even
though it is a 4-seater. Chassis engineers will love this car.
The rest of the chassis is also up to standard. Suspensions are
double-wishbones up front and 5-link at the rear. Steering is by
electric assistance to save weight. Brakes are also pretty big
(323mm front, 302mm rear).
RX-8 weighs only 1300kg, about the same as RX-7, or undercutting
a BMW 330Ci by 200kg. We must praise its attention to weight
control.
The RENESIS Engine
We have mentioned that the new rotary engine made a breakthrough
in fuel efficiency and emission level. How did it work out? in
the past, rotary engines had their exhaust ports located at the
face of the combustion chambers. This made packaging easier but
there are 2 disadvantages: firstly, it creates overlapping
between intake and exhaust phase, thus exhaust gas always
contaminate fresh air and fuel mixture, reducing burning
efficiency and worsening emission. Secondly, because the exhaust
port is at the outer surface of the combustion chamber, any
residual fuel failed to be burnt in combustion cycle will be
pushed towards the exhaust port by rotor tips. As a result, the
unburned fuel will emit from the engine directly and adds to the
pollutants.
Unexpectedly,
Mazda solved these problems easily by relocating the intake and
exhaust ports to the side of the combustion chambers. As a
result, overlapping between intake and exhaust phase no longer
exist. Now fresh air and exhaust gas are separated. Besides, any
unburned fuel will not enter the exhaust ports easily because
the ports are distanced from the outer surface of combustion
chambers. Instead, the residual fuel will be carried over to the
next combustion cycle and burn out completely.
Furthermore, side intake and exhaust ports bring 2 more
advantages. Firstly, the outer surface of combustion chamber is
now smooth thus easier to lubricate. This reduce the wear on
rotor tip sealing and eventually improve durability, which was a
headache of older rotary engines. Secondly, by moving the ports
to the side, Mazda find space to enlarge them considerably. For
example, the intake ports are 30% larger than that of the old
13B engine used by RX-7. This of course improves breathing
smoothness and lifts power output.
Unfortunately, the RENESIS used by RX-8 is normally aspirated
only. It displaces the same as RX-7, that is, twin rotors with a
total displacement of 1308 cc. Because a rotor chamber combusts
once every revolution, compare with piston engine’s once every 2
revolutions, its effective displacement is actually 2616 cc by
the norm of piston engines. The RX-7 with twin-turbochargers
generated 280 hp in its final phase of development. Without any
forced induction, the RX-8 can still achieve 250 hp (240 hp for
European version), very good for a 2.6-litre engine. Its power
curve is peaky though - maximum power occurs at 8500rpm. The
turbine-like engine can spin to a genuine 9000rpm, no joking.
This
remind me another famously peaky engine - Honda S2000's F20C
VTEC engine. Believe or not, despite of the vast differences in
their design and architecture, these two engines are very close
in their behaviour - the Honda reaches max power at 8300rpm,
both cut-out at 9000rpm, both are rated at 250hp (JIS) and 240hp
(DIN), and both have a weak torque curve. In the Honda case, it
is 160 lbft at 7500rpm. Mazda is slightly better, 159 lbft at a
more useable 5500rpm. But that’s still not anything to be proud
of.
The 250hp / 240hp RENESIS engine is equipped with a 3-stage
variable intake manifold. Mazda also offers a cheaper version
RX-8 (around 10% cheaper), whose engine has just a fixed intake
manifold which is tuned for low-down torque rather than high-end
power. The result is slightly higher maximum torque and is
reached at slightly lower rev, but the engine cuts out at just
7500rpm and eventually deliver less power - 210hp at 7200rpm for
Japanese version or 192hp for Europe version. The cheaper RX-8
also runs a cheaper gearbox - 5-speed manual instead of the high
power version’s 6-speed manual. Seems that it is not cheap
enough to justify the loss in performance.
On the Road
As before, the rotary engine is incredibly smooth. Its power is
produced linearly across the sky-high rev range. Perhaps too
linear, you need at least 4000rpm to get sufficient performance.
Due to the lack of torque, RX-8 doesn’t feel as fire-breathing
as other 250-horsepower cars, say, Audi TT V6. Luckily, its
6-speed gearbox is low geared and has close ratios to keep the
engine boiling, and the shift is super-slick to encourage
frequent changes, which is a must in order to extract the
performance it deserves. Mazda claims a top speed of 150mph and
0-60mph taking 6 seconds flat. Considering the 40kg lighter
Honda S2000 does that in 5.6 seconds, Mazda’s figure is totally
believable.
Around
town, the Wankel engine is pretty tractable. On motorway, 60mph
in 6th gear, it runs at a quiet 3000rpm, so cruising refinement
is good.
Well, this normally-aspirated version of Wankel engine may not
match a proper big capacity V6, but its packaging advantage is
shown in handling. In the world of 4-seater coupe, no one else
can match it in chassis balance - not even BMW 3-series Coupe.
This car is so composed, so smooth and so agile in corners. No
matter how hard you abuse it, it remains safe and neutral. There
is just not enough torque to induce dramatic oversteer or slide
at the rear wheels. Therefore the high-threshold traction
control is rarely used.
The steering is another delight. Turn-in is instantaneous and
precise, because there is so little weight at the nose. The
steering also transfers good road feel to the driver’s hands,
despite of its electrical assistance.
Suspension is well sorted, delivering a firm but well-damped
ride in the same way as BMW M3. As a result, RX-8 remains stable
in cornering.
Verdict
Priced at US$27,000 in the USA or £22,000 in the UK, the RX-8 is
around 10% cheaper than a comparable equipped Nissan 350Z,
15-20% cheaper than Audi TT 225hp, 25% below Audi TT V6 and
undercut BMW 330Ci by 30%. Unquestionably, it is a bargain. No
wonder Mazda sets an ambitious target of selling 30,000 cars a
year.
Comparing RX-8 with others is not easy, because it is so unique
in all area. It is a full 4-seater coupe, it has sports car
performance and handling while it is priced at the same level as
super hot hatches. If we compare it with Alfa 147GTA or Golf
R32, the Mazda will definitely run away with its superior
handling and sophisticated image. If we compare it with BMW
330Ci, it will also beat the German car by handling and impress
people by its unusual character and bargain price. Nissan 350Z
is faster, but it offers 2 seats only thus is not a direct
competitor to RX-8. Maybe the next generation RX-7, if Mazda
greenlight it, can rival it. Both Audi TT 225 and V6 are
actually 2+2. The 225 is outpaced, outhandled and undercut in
price by the Mazda. It’s also an old car, so you can forget it.
The TT V6 has a remarkable engine and transmission combo, but it
is also a lazy driver’s car. In contrast, Mazda RX-8 is the real
driver’s car. Its precision and feel inspires you to drive
faster and faster, and eventually reward you with higher level
of satisfaction. A new class leader has been born.
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