Street Smokin' STi

A Subaru Impreza STi with a 2.5 block and plenty of bucks invested in the good gear.

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images

At a glance...

  • 2004 Impreza Sti
  • 2.5 litre US-spec block
  • Big turbo and wastegate
  • Top-line gauge-ware and audio
  • A potent package

When you take your car to a dealership for factory servicing you kinda expect everything to go smoothly. That’s exactly what Paul X, a dedicated young car enthusiast, thought - until he took his Nissan 200SX for a routine 25,000km spanner session...

It’s common practice for workshop technicians to take each car for a test drive after servicing. But what isn’t common is when the third year apprentice takes the car for a test drive at speeds of around 130 km/h - and then loses control...

So while Paul toils away at work, his immaculate black S15 leaves the road and impacts heavily with a pole. Sideways. The carnage extends from virtually bumper to bumper - there was no possibility of repair for this machine.

We can only imagine what was said when the dealership phoned Paul to tell him the news...

Twelve months of legal proceedings followed until, finally, Paul ended up with a wad of cash. But what would he buy to replace his beloved 200SX? Well, it definitely wasn’t going to be another Nissan, so he returned to the marque that had served him in the past - Subaru.

Paul signed on the dotted line for a 2003 Impreza STi with a limited edition S20-SC pack. The S20-SC pack was offered only by Subaru Docklands (in Melbourne) and comprises a short-shift mechanism, an exclusive gear knob, re-trimmed seats and door trims, stickers and a numbered plaque - only 10 were built.

Having already owned a ‘99 WRX Club Spec and two door STi, Paul knew pretty much what to expect from the later-model STi. The performance is familiar but the 2003 STi is more refined, comfortable and has a substantial feel.

"Still, it was laggy like a dog," says Paul.

After just 3 days of ownership Paul invested in a Michael South dump pipe and an A’PEXi GT cat-back exhaust. A prototype Hyperflow front-mount intercooler kit was also installed - Paul had previous work performed by Hyperflow and was more than willing to be a guinea pig. Once the big ‘cooler was installed, turbo boost pressure was increased by a few psi. Paul says the standard ride height is also way too high so a set of King Super Low springs went into the struts. Stray birds have no chance diving underneath when this mighty STi is bearing down on them!

With this mechanical configuration Paul took the car to the magnificent new Western Sydney drag strip and ran a best time of 12.64 seconds. We’re told this is a time few people can match with similar mods but, then again, Paul doesn’t display much mechanical sympathy...

Not coincidentally, the standard engine spun a bottom-end bearing with just 38,000km on the odometer. Paul didn’t bother trying to make a warranty claim with this one - it was time to get serious and do things his way.

Keen to take the opportunity to improve the STi’s lack of bottom-end torque, Paul ordered a 2.5 litre short block from the US and crammed it with forged pistons (the compression ratio remains virtually stock). The new motor was carefully assembled by Southern Motor Works in Wollongong. A GReddy oil catch can and Process West engine oil cooler were also added.

Paul can now laugh about the original engine’s death - but a second catastrophe wouldn’t be so humorous...

With a ‘big block’ motor as the platform, a set of TurboXS extractors serve to conduct exhaust gas to a Garrett GT35 ball-bearing turbocharger. Mounted together with a 48mm Turbosmart external wastegate, Paul says the 3 inch dump pipe j-u-s-t clears the firewall. Note the XTR turbine jacket and exhaust manifold heat wrap which reduce under-bonnet temperature and maximise turbine efficiency.

Boost pressure is normally set to around 19 psi, but Paul has pushed it further on the odd occasion. Thankfully, the latest-and-greatest Hyperflow front-mount intercooler has also been bolted on - it’s a monstrous bar-and-plate sucker measuring 720 x 250 x 114mm. Plumbing to the core is 2 ½ inch while the outlet plumbing is 2 3/4 inch. An APS blow-off valve is fitted as part of the system. The pre-turbo air intake comprises a Hyperflow aluminium airflow meter housing, cold air induction and K&N pod filter.

At the time of writing, Paul relies on a UTEC interceptor module. The injectors are 800cc Sard items teamed with MRT rails and a Bosch Motorsport pump. Unfortunately, we’re told that the airflow meter signal is maxing out and the interceptor is struggling under the conditions. Paul sounds keen to switch to a new MoTeC M800 plug-in programmable ECU. The fuel system also needs to be revised as it appears the 800cc Sard injectors are running flat-out – given their quoted fuel flow, they should be running well within their capacity.

Paul says one of the biggest advantages of the late-model STi is the strength of its 6 speed gearbox - it continues to operate when the previous generation 5 speed would be shattered into pieces. The clutch also remains standard but it does slip when boost is cranked to around 23 psi. An aftermarket upgrade is on the cards for the near future.

Paul says his STi sits brilliantly on the road - no doubt aided by its downforce and grippy Falken Azenis RS 225/45 18s. It turns sharply, holds its cornering line tenaciously and gets its power down from the apex for a mind-blowing getaway.

Aside from the King springs, the only other suspension mod is a Whiteline 24mm rear swaybar with heavy-duty links. The standard Brembo braking system is capable of dislodging your eyeballs so not much has been needed here - only some DBA replacement front discs and Pagid pads.

Open the door and you’ll find the standard STi S20-SC trim - with a couple of eye-catching extras thrown in...

The first thing you’ll notice are the Defi electronic gauges for boost pressure, oil pressure, fuel pressure, EGT and oil temperature. These are distributed in an on-dash triple gauge pod, the driver’s and front passenger’s air vents. Paul admits these gauges weren’t cheap but, hell, they look the biz - and serve a useful function! Given the appeal of these gauges it’d be a bit bizarre to whack in an el cheapo audio head unit so, again, Paul went all-out and bought a top-line Sony minidisc unit.

Paul says he’s already invested a lot of money and effort in the car but says, with a couple of minor tweaks, it should be completed. A MoTeC M800, revised fuel system and beefier clutch will finish things off nicely.

Paul is not one to back away from a challenge and believes the car should run an easy 11 second pass once the final spit and polished has been done. He knows he’ll be up against it, though, because the close-ratio 6 speed requires so many up-shifts.

But that’s a concern for another day.

Now that Paul (finally) has a hot car back in his garage, he’s lost his driver’s license...



Paul now has some points back on his license and is returning the car to standard for sale. He says he’ll be giving the whole go-fast scene a miss for a while...


Hyperflow                                                     +61 2 4283 2281

Southern Motor Works                               +61 2 4256 6429

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