Impreza WRX STI
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After 2 generations and many small
evolutions, STI suddenly becomes a hatchback !
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The
name STI, short write for "Subaru Technica International", is no
stranger to our readers. It is the motorsport arm of Subaru as well as
its performance division. In the road car side, its core business is to
modify Impreza (as well as a handful of Legacy and Forester) into the
high-performance STI versions. Since its birth in 1994, this car had
won so many praises from car enthusiasts all over the world and has
been regarded as one of the greatest A-to-B cars in history. Its fame
matches the great Audi Quattro and Lancia Delta Integrale, which says a
lot.
Now let's turn to the new generation Impreza WRX STI. The biggest
change you will notice is its form - bye bye the 3-box sedan chassis,
enters the 5-door hatchback body. While fans may criticize it for
becoming too European mainstream, Subaru would be glad to point out
that a hatchback is shorter (by 50mm) than a sedan thus lowers polar
moment of inertia - the key measurement for agility. This is also why
its WRC rivals (Ford Focus, Citroen C4 and Peugeot 206) performed
better in recent years.
Going from the regular WRX to STI is about as different as from Audi S4
to RS4 - you can feel the former is mass production while the latter is
truly exclusive. Observing from outside, the STI looks really
fire-breathing. It has muscular fender extensions, large air intakes
and vents, wide air dam, large tailgate spoiler and eye-catching
18-inch alloy wheels shod with 245/40 rubbers. Front and rear tracks
have been widened by 45 mm and 40 mm respectively, while the overall
width is 55 mm wider than WRX. In addition to the longer wheelbase and
shorter overhangs sharing with the new Impreza, this car gives you a
sense of immense stability that the last generation car lacked of.
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Longer wheelbase and wider tracks give
you a sense of immense stability...
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Open
the bonnet, you will see a familiar boxer engine with intercooler
sitting atop. The Japanese version still displaces 1994 cc thanks to 92
mm bore and 75 mm stroke. Compare with the old car, it has the
following enhancement: 1) Exhaust valves also get AVCS variable valve
timing; 2) Turbocharger gets reshaped compressor wheel for higher
efficiency; 3) Enlarged intercooler and enhanced air flow through the
engine compartment improves cooling efficiency; 4) Exhaust muffler gets
larger and is now mounted transversely to reduce backpressure. Quad
tailpipes have similar effects. 5) Twin-scroll IHI turbocharger
eliminates interferences among exhaust flow from different cylinders.
Overall, the Japanese motor generates 308 horsepower at 6400 rpm, 28
more than before. Also worth noting is that it no longer follows the
domestic voluntary limitation at 280 hp. Maximum torque remains
unchanged at 311 lb-ft / 4400 rpm, though the torque curve is flatter,
with at least 90 percent of the max value from 2400 rpm.
The export version (USA, Europe and Australia) continues to employ a
larger 2457 cc block with 99.5 mm bore and 79 mm stroke. Thanks to the
additional capacity, it can employ a single-scroll turbocharger running
at lower boost pressure without hurting performance. Max power and
torque are 305 hp / 6000 rpm and 290 lb-ft / 4000 rpm respectively for
the USA market, or 300 hp / 6000 rpm and 300 lb-ft / 4000 rpm
respectively for Europe. Of course, it loses some of the high-revving
excitement of the 2.0-liter engine, which is evident from its 7000 rpm
cut-out instead of the Japanese motor's 8000 rpm. In return, it
compensates with stronger mid-range torque and, perhaps most important
to Subaru's engineers, the ability to comply with the stricter emission
standards in Europe and USA. Surprisingly, according to factory
figures, the 2.5-liter engine is actually more frugal.
Both
engines have added
SI-Drive, a selectable engine mapping which has been overstated by
Subaru recently. While most other "comfort / normal / sport mode"
systems alter throttle response, suspension damping and steering
assistance simultaneously, the Subaru system affects only the engine.
It offers 3
modes - "Intelligent" mode is designed for economy, thus results in
softer throttle response and lower rev limit. "Sport" mode releases
full rpm and quicken throttle response, while "Sport Sharp" enables
even sharper response. Frankly, it is not worth any more descriptions.
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SI-Drive is overstated, but the
308-horsepower boxer is no joke.
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The
drivetrain is similar to the old STI. In other words, it employs a
6-speed manual gearbox, Torsen (Helical) front and rear differentials
and an active center differential called DCCD (driver controlled center
differential). The latter normally distributes 41 percent torque to the
front wheels and 59 percent to the rear wheels by means of planetary
gears, but its multi-plate clutch can be locked up to send up to 50
percent torque to the front. Through a control button on the center
console, the driver can vary the torque split between 41:59 and 50:50
in 6 steps. That is more or less the same as the last generation STI.
What really new is the additional Auto, Auto – and Auto + modes. Auto
lets the computer to determine the best torque split depending on
traction status. Auto – reduces the intervention of multi-plate clutch,
thus is easier to oversteer than Auto. In contrast, Auto + tightens the
multi-plate clutch, thus shifts more torque to the front and increases
understeer.
All these sound sophisticated. However, compare with Mitsubishi's S-AWC
system, the Subaru system seems less remarkable. Evo X has active yaw
control to vary the torque split between the rear wheels according to
needs. In contrast, the STI's Torsen LSD is a mechanical and passive
device, therefore it cannot induce understeer or oversteer like the
Mitsubishi. Yes, through the active center differential you can still
influence the steering attitude, but it is far less effective than an
active rear differential, especially that the DCCD can only vary torque
split for a very narrow range (from 41:59 to 50:50) - so narrow that
the 6 manual steps seem rather unnecessary ! Another advantage for the
Evo X is that its S-AWC system integrates ACD and AYC with stability
control, while the STI's DCCD and VDC stability control are separated
systems. You can see which system is more sophisticated.
Compare with the regular Impreza, the chassis of STI gets some
structural reinforcement by means of high-strength steel while the
bonnet is converted to aluminum. The engine is rigidly mounted to the
chassis to reduce movement. The front suspensions employ inverted
dampers for greater rigidity and aluminum lower control arms for less
unsprung weight. Like the rest of the range, STI has its engine and
center differential mounted lower than the old car to benefit center of
gravity. Most important, the new double-wishbone rear suspensions
should provide better ride and handling precision than the old
MacPherson struts. At 1480 kg, the whole car weighs only 20 kilograms
more than the last STI. Such weight control is obviously more
successful than Mitsubishi Lancer Evo X, which gained 130 kg. Despite
that, the STI still employs powerful Brembo brakes all round.
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DCCD can vary torque split from 41:59
to 50:50, though it can't suppress understeer as well as Mitsubishi's
AYC...
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On the Road
Just as we can predict from the technical specifications, on the road
the new STI gives no surprises in engine and performance. Its 2-liter
turbocharged engine is quite laggy by today's standard, although not
bad for an engine producing 150 horsepower from each liter of capacity.
Power delivery feels flat until 3000 rpm, when it starts picking up
linearly towards the high 7000 rpm. The 2.5-liter engine is better in
this aspect, as it provides more torque low down. It also produces a
more satisfying boxer exhaust note than the Japanese motor because of
different connection of exhaust pipes.
Against the clock, both 2.0 and 2.5-liter STI accelerate from 0-60 mph
in around 4.8 seconds and 0-100 mph in 13 seconds. Top speed is
estimated to be 158 mph, mainly limited by the 0.36 drag coefficient.
Such performance is still outstanding today, but it represents no
progress at all from its remarkable track record. You can find from our
Graveyard archive that the STI Version V
of 1997 was already capable to do 0-60 mph in 4.6 seconds and 0-100 mph
in 12.3 seconds. 10 years have gone and the car stays the same - or
even slightly slower ! Can you satisfy ?
Well, this is the same problem Mitsubishi Lancer Evolution is facing.
The Japanese have to come up with a new idea how to improve their
performance. Otherwise European car makers may catch up quickly. Watch
out Audi RS3.
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STI is still the fastest A-to-B car on
the earth beside Lancer Evo X...
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However,
drive the new STI through a series of corners and undulations, you will
find its biggest improvement is suspension. While the old car used
stiff springs to control its body movement, the new car's
wheels-at-corner structure and double-wishbone rear suspensions allow
much more compliant ride and better refinement while body control is
still tight.
As always, the traction and grip from the permanent four-wheel drive
system is excellent. You have the opportunity to set the DCCD and
stability control to bias towards the safe side or the fun side. At the
most rear-biased torque split and VDC at off mode, you can enjoy
pushing the car to the limit at each corner until feeling it drift on 4
wheels. The brakes and the steering also give you confidence to attack
corners at speed unimaginable in other European hot hatches. Yes,
Impreza STI is still the fastest A-to-B car on the earth beside
Mitsubishi Lancer Evo X.
Some people may criticize its looks for too ugly, but do they realize
the old car was uglier still ? Some people dislike its cheap,
hard-plastic interior, but why didn't they say the same things to the
old interior, which was even cheaper and more cramped ? The new STI
does have some flaws, but they cannot eclipse its exceptional on-road
competence and the fact that it is easier to live with than ever.
Although I still prefer the early STI based on the first generation
Impreza, the latest one undoubtedly deserves our admiration.
Impreza WRX STI vs Lancer Evo X
Impreza STI and
Lancer Evo series have always been a legendary rivalry no matter for
road cars or rally cars. The first Evo was born in 1992, the same year
as the original Impreza WRX. As the Mitsubishi evolved to be more
serious, Subaru responded with the STI version in 1994. Since then "Evo
vs STI" became the most frequently appeared topic in car magazines. So
how are these arch-rivals compare in their latest rematch ?
By figures, the STI has a sizable advantage in power - 308 hp vs 280 hp
for Japanese version - and the same torque, but we all know that the
Mitsubishi's figure is underrated to satisfy voluntary limit. What
really advantage to the Subaru is kerb weight, which is 60 kilograms
lighter than the Evo X equipped with 6-speed dual-clutch gearbox. That
is why the STI is found to be quicker in straight line. It takes about
4.8 seconds to go from 0-60 mph (Evo X: 5.0 seconds) and 12.9 seconds
for 0-100 mph (Evo X: approx. 13.3 seconds). The boxer engine sounds
more characterful, but the Mitsubishi inline-4 has quicker throttle
response and less turbo lag at low rpm. Mitsubishi's paddle-shift SST
gearbox is also a strong advantage, thanks to its easy and
uninterrupted gearchange.
Both cars are kings of mountain roads, but the Evo X handles better in
various aspects: sharper turn-in, more neutral cornering attitude and
slightly more communicative steering. Its integrated S-AWC (including
AYC) is proved to be cleverer than the DCCD of STI. Although sometimes
it could feel artificial, it places the car more precisely in corners
and therefore feels more agile to control. The STI is still a fabulous
driver's car, but it often reveals more understeer. On the positive
side, it has slightly better ride and braking.
The Evo X shines not only in handling, but also styling and interior
quality. It feels much more expensive than the Subaru. Overall, the Evo
X is the winner in this contest. |
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The
new Impreza is longer, wider and taller than the outgoing car. Its
wheelbase gains 95 mm to 2620 mm, matching most other C-segment rivals.
The longer wheelbase intends to improve interior
space as well as ride quality. The front suspensions continue to be
MacPherson
strut type, but the rear ones switch to double-wishbone type for
several reasons: 1) improves geometry hence road holding; 2)
improves ride comfort; 3) reduces intrusion into the boot hence
boosting luggage space. Despite of the larger size, the new car weighs
about the same as before due to clever structural design and the use of
high-strength steel. 
Forget
the bread-and-butter naturally aspirated Impreza, what car enthusiasts
concern is the turbocharged version. This starts from the S-GT and WRX,
and is going to be toppled by STi next year. 
For overseas market – most
important of which is the United States, Subaru continues to use the
WRX nameplate. It is available in both hatchback and sedan form. As
usual, the overseas WRX employs a larger, 2.5-liter version of the
boxer engine but runs at a lower turbo boost. It produces 224
horsepower at 5200 rpm and 226 lb-ft at 2800 rpm. The peak output is
slightly down on the old car but they arrive lower down the rev. Both
S-GT and WRX engines mate with the old 5-speed manual gearbox whose
shift action is slightly notchy. It transfers power to all 4 wheels via
a center differential with viscous coupling differential lock. The
torque split is 50:50 front to rear.
As a driver's car, we also
concern how fast it is against the clock. The WRX does 0-60 mph in
around 5.8 seconds while the more powerful S-GT should return 5.5
seconds. These figures seem excellent for any hot hatches, but
remember, 4-wheel-drive machines always display superior standing-start
result due to the extra traction. A better indicator to its performance
is 0-100 mph, for which the WRX takes 16.2 seconds. This is almost two
second slower than an European Renault Megane R26 and Opel Astra OPC.
Again a huge disappointment to the supporters of Impreza.