Cubed-Up STi

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.

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...

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.

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.

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.

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.

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.

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...

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.

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...

Contact: C-N-J Motorsport +617 3290 3966 www.cnjmotorsport.com.au

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