Full Test: 2008 Subaru Impreza WRX STI

We know you. If someone tossed you the keys to a spanking-new 2008 Subaru Impreza WRX STI for the weekend, you'd make a beeline for the nearest winding road leading into the mountains. So would we.

But would you also bring along your wife, two kids and mother-in-law, all prone to carsickness? Not if you could avoid it. But we couldn't. Such is married life. Besides, Mom was the one with keys to the cabin.

Normally, the mere sight of an old-school STI or Evo complete with a boy-racer wing would have been enough to elicit a Pavlovian response from this bunch, with the gut-churning getting into high gear even before we reverse out of the driveway — but such was not the case this time.

Because the 2008 Subaru Impreza WRX STI is based on a sensible wagon-esque five-door hatchback body instead of a sedan, it somehow managed to slide under the radar of civilians. Good thing, since this revised, turbocharged 2.5-liter flat-4 engine puts out 305 horsepower and it makes the 2008 STI go like stink.

It Had To Be Done
Subaru has been getting its butt kicked in WRC rallying of late, losing out most often to hatchbacks from Ford and Citröen. Petter Solberg, Subaru's WRC rally ace, convinced the brass at Fuji Heavy Industries that a five-door hatch was the way to go this time, citing aerodynamic benefits and "better handling."

In fact, despite sitting on the same 103.3-inch wheelbase as the new WRX sedan, the five-door's overall length is 6.5 inches less, representing a substantial reduction in polar moment of inertia, which is a big chunk of the "better handling" part of Solberg's argument.

Since the STI exists to homologate the car used in FIA WRC and Group N rally competition next season, that's why we've got an STI wagon, er, hatchback today.

Besides, in STI garb, the five-door Impreza body actually looks mean. Substantially wider fenders are rendered in steel on a unique unibody and complement a track that's wider than that of the WRX by 1.3 inches in front and an amazing 2.5 inches in the rear. Last year's STI was some 1.5 inches slimmer.

Let's Get Functional
The five-door decision pays dividends on the run up to Grandma's house, as the five of us, plus baggage, fit with ease. With fewer aboard, the 60/40-split rear seats fold down — a first for the STI — opening up some 44 cubic feet of cargo space.

Space for our drivers proves ample, and a telescoping steering wheel and height-adjustable seat accommodates all. Handsome seats clad in a combination of artificial suede and leather strike a good balance between comfort and support for daily use, but we can see how hard-core track-day addicts might want something more suitable for high-G maneuvers.

So it's a shame that the ultrasupportive Recaro seats available in Japan are not on the options sheet here. Word is that a version incorporating the U.S.-required passenger-detection sensor for airbag use hasn't been certified, but Subaru may decide to do so in the future.

Punch It Already
Even at sub-puking cornering speeds on our drive through the mountains with the family aboard, the positive effects of the new STI's longer wheelbase and wider track are readily felt as excellent steering precision, a lack of pitch and improved driver confidence — not to mention no carsick companions. Once the passengers were dislodged at our destination, we were able to do some driving at a more furious pace. The STI came alive — but not like the old one.

Push a bit harder and the conversion of the Impreza's rear suspension from struts to a double-wishbone layout instantly makes sense. Midcorner bumps and heaves don't break the car's composure, either. This WRX STI stays dead stable and the grip is tenacious. The chassis feels slightly softer over seams and cracks than before, but it's that extra compliance — and a more favorable camber curve for the rear wheels — that keeps the car's tires planted on the pavement.

At the test track, the sum of these changes helps the 2008 STI to a 72.0-mph slalom run, blowing the 2006 STI's 68.1-mph speed out of the water. The last Mitsubishi Evo IX we tested went 70.7 mph, which is closer, but still no cigar.

Our 2008 STI's 0.90g skid pad performance (while exceptional) is slightly below the old car's 0.93g effort. Perhaps the 245/40R18 Dunlop Sport SP 600 tires don't have as much ultimate grip as the Bridgestone Potenza RE070s of old. At the same time, we couldn't feel the difference on the open road, where real corners that feature direction changes more closely mimic the slalom.

Beneath the Bonnet
The 2008 edition of the STI's turbocharged DOHC 2.5-liter flat-4 now has variable valve timing on the intake and exhaust cams, facilitating both a wider torque band and an increase in power. Consequently, the STI now makes 305 hp (up from 293 hp) at 6,000 rpm. Torque remains fixed at 290 pound-feet, but it now punches in earlier, peaking at 4,000 instead of 4,400 rpm.

Squeezing the throttle produces a surge of thrust that begins deeper in the rev range and bolts straight for the 6,700-rpm redline (the redline was 7,000 rpm last year), especially in 1st gear. By the time we see the tach-mounted shift light, it's too late. Note to self: Shift earlier next time.

All-wheel drive launches the STI through the wider 245/40R18 rubber now and this makes for demon starts, and our STI cleared 60 mph in just 4.8 seconds and rendered the quarter-mile history in 13.3 seconds at 102.3 mph. Getting to 60 mph requires two deliberate upshifts (and pauses in progress), as the six-speed transmission has rather short gearing and doesn't change gears quickly, either.

The Japanese-specification WRX STI is equipped with Subaru's turbocharged 2.0-liter horizontally opposed four-cylinder. The major modifications over its predecessor are the addition of a different twin-scroll turbocharger, a bigger intercooler and variable valve timing now on both the inlet and exhaust side.

The Japanese 2.0-liter engine's output is almost the same as the U.S.-spec 2.5-liter engine, with 304 hp available at 6,400 rpm and 311 lb-ft of torque at 4,400 rpm, but this engine has a narrower power band. Subaru engineers tell us that Japanese drivers like the smaller engine's livelier personality, while American drivers prefer the larger engine's drivability.

Gas and Go
Subaru recommends 93-octane fuel for the best performance — the 305-hp rating was earned using the stuff — but here in California we can only get 91 octane, the STI's minimum requirement. Clearly, a bit more improvement in acceleration is on the table.

At least the brakes are more than a match for the acceleration. The only major change to the Brembo system is a 0.3-inch increase in the diameter of the vented front and rear rotors, yet stopping distance improves significantly from the 115 feet we recorded on a 2006 STI to a remarkable 106 feet for this one.

New for 2008 is something called SI-drive, a system that allows the driver to choose one of three settings that affect the engine and electronic throttle maps. Sport is the default, and Sport Sharp makes the throttle pedal more sensitive. Intelligent mode cuts power and torque, puts the throttle pedal in a relaxed state and activates an economy-oriented shift light.

What's the Big Diff?
Actually, there are three of them. The front and rear are strictly mechanical limited-slip units — helical up front and Torsen in back. The center differential is the complicated bit.

Nominally, this center diff is a planetary gearset that apportions torque 41 percent front and 59 percent rear. It's paired with an electronically controlled clutch-type limited-slip differential that is tied into the stability control hardware and software.

Three computer-regulated Auto settings are now provided instead of one. The familiar six-way manual settings intended for competition situations and gravel carry over from the previous STI setup.

The Auto setting provides wide-ranging torque-bias control over the broadest range of conditions. Auto Plus is geared toward looser surfaces (gravel or snow) and therefore tightens the differential and reduces the rear-drive bias. Auto Minus is best for dry roads, as it frees the center diff to reduce drivetrain binding while it sends more power to the rear wheels. But the computer still makes continuous adjustments in response to driver inputs. Got it?

The difference between the three settings is readily apparent. We flogged the STI on a dirt surface or two, and we could clearly feel the diffs working differently from corner entry through to the exit. But honestly, there might be more settings here than you could possibly use, and engaging the manual diff on the pavement could break stuff — really expensive stuff.

Make Mine Blue
Or gray — it doesn't much matter. The 2008 Subaru Impreza WRX STI is an impressive car because every change has made it better. And it was damn good before. But this comes at a slightly raised price. The cost of entry for a plain STI is $35,640, compared to $34,120 for the 2007 edition. For that you get everything except a navigation system and the optional BBS forged-aluminum wheels that reduce unsprung weight by about 7 pounds at each corner. Our car had both of these options and stickered at $39,440.

It's worth it. The 2008 Subaru Impreza WRX STI performs better than the outgoing car in most performance tests and feels better on the road. It also happens to have a more useful and functional interior with space to haul stuff while you haul butt.

The 2008 Subaru Impreza WRX STI proves that you can have your cake and wring its neck, too. Just remember to leave the spousal unit and kids at home first.

The manufacturer provided Edmunds this vehicle for the purposes of evaluation.