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Cubed-Up STi

A MY00 STi with more cubes than it's supposed to have!

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images

At a glance...

  • MY00 STi 4 door
  • 2.5 litre
  • Focus on useable grunt
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It’s interesting how people’s focus shifts after they’ve owned a modified car or two. Just ask Steve X of Brisbane.

Steve previously owned a Subaru WRX with the usual collection of bolt-on go-fast goodies. Using an IHI VF34 turbocharger, the Subie put out more than 150kW at all four wheels – but focussing on the top-end power output paints a very incomplete picture.

"It went well when I deliberately drove it but it was a bit laggy and with an automatic transmission it didn’t come together quite right," he says.

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About two and a half years ago Steve decided to cut the WRX loose and step up to the next level of off-the-shelf Subaru performance – a MY00 STi 4 door.

"I’d always wanted that model STi since it came to Australia and when second-hand ones dipped down to a manageable price I thought, yep – I’ll have one..." says Steve.

Steve had already removed the 3 inch exhaust from his previous WRX so, rather than have it consume space in the shed, he whacked it on the STi. And then it started pouring mods...

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What you’re looking at here is a built-to-order C-N-J Motorsport 2.5 litre flat-four with an emphasis on response and accessible mid-range grunt. Steve uses the car as a daily driver and enjoys the occasional club driving event and he learnt one all-important lesson from his old WRX – it’s easy to make power, but power and accessible torque are quite another thing...

The platform for the build is a Subaru Forester XT block, which we’re told is virtually the same as the US-spec STi unit. Internally, the crankshaft has been lightly modified and balanced, the rods are custom and forged pistons provide a static compression ratio in the 8s. The original STi heads were carried over to the 2.5 engine and now incorporate custom cam profiles, aimed at satisfying Steve’s mid-range cravings. The cylinder heads are tidied up – C-N-J says the biggest flow limitation appears to be valve size.

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Note that the larger capacity engine called for a suitably upgraded coolant radiator. Kelvin from C-N-J explains that the US-spec 2.5 STi uses a 20 percent larger radiator than the local 2.0 litre STi, so they followed that lead as a precaution. The radiator in Steve’s car is as big as would fit without cutting metal – it offers a 40 percent greater volume than stock.

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Just to be on the safe side, the cabin is also equipped with a centre gauge pod with HKS water temperature, oil pressure and boost pressure meters.

From the exhaust ports, spent gasses are sent through a custom C-N-J design tuned-length and stepped header extractors with an AVO 400hp turbocharger. A C-N-J split-dump exhaust ensures the turbine breathes easy. On the intake side, a pod filter draws air from inside the front guard. The blue silicone pipe into the turbocharger is an AVO item.

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With boost pressure to a maximum of around 23 psi, charge-air cooling is an issue that can’t be ignored. Steve’s car runs a high-quality APS front-mount intercooler kit, which includes a silicone pipe into the throttle. An APS recirculating blow-off valve is also fitted.

Fuelling the 2.5 litre EJ flat-four are high-flowed standard injectors fed by a Walbro high-flow pump. The ignition is the standard MY00 set-up with high-tension leads.

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Controlling fuel, ignition and boost pressure activities is a plug’n’play Autronic SMD (D representing direct plug-in). Intended for Group N rally use, the SMD upgrade gave C-N-J full tuning control and allowed removal of the airflow meter. Only the airflow meter housing remains.

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This Dyno Dynamics chassis dyno graph shows what Steve’s STi has to offer. Sure, the top-end of 252kW ATW is nothing to be sneezed at but check out the meaty-mid-range – it’s the envy of many turbocharged fours producing similar power. Boost pressure is also shown on the graph – 23 psi is held through the entire sampled rev range. And note that there were no fancy fuels or additives used – just straight 98 RON pump fuel.

Steve says the torque that he finds - even on a leisurely drive to work - is amazing. If someone pulls alongside it’s no sweat. There’s no need for a big launch - just put your foot into it and let that big rush of torque send the competition into the mirrors. Steve rarely needs to take the engine past 5500 rpm...

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With oodles of mid-range torque, C-N-J were careful not to fit a clutch that would result in a smashed gearbox within the first few weeks on the road. A modified Daikin full-face clutch has been performing admirably, but Steve is all-too aware of the gearbox situation – he’s pretty sympathetic with it. If a STi 6 speed or an aftermarket synchro gearset appears on the market, don’t expect him to sit back and do nothing...

The STi comes factory fitted with a pretty aggressive suspension tune and a carbon fibre front strut brace so there’s not a lot of need to upgrade to anything more extreme. All Steve’s fitted are a set of lowered aftermarket springs.

It’s a similar story with the STi brakes – there are Zeal rotors, Endless pads and braided lines on the front.

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Cosmetically, a STi is always a distinguishable beast – the towering rear wing and body kit are hardly subtle. The only external mods to Steve’s car is Racing Hart CP035 17s wearing 215/45 F1 rubber.

With a tidy sum of money invested in the car, Steve is understandably reluctant to purchase a replacement in the near future. But there’s one final modification on the horizon – a slightly smaller HKS turbo to provide even better response and useable torque.

Peak power? Well, it might suffer a small amount but, as we said, it’s interesting how people’s focus shifts...


C-N-J Motorsport
+617 3290 3966


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