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Spare Nothing STi

A 2.5 litre Subie STi with everything you can throw at it!

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images

At a glance...

  • Factory MY00 STi
  • 2.5 litre block and high-strength internals
  • 356kW at the hubs
  • Full driveline upgrade
  • Adjustable suspension
  • The works!
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The goal for this MY00 Subaru STi build-up was clear: generate as much power as possible while maintaining good on-road manners and total reliability.

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Straight away, this criteria means it’s not a matter of bolting on a humungous turbocharger, boosting the brains out of the engine and keeping your fingers crossed. A well thought-out plan of attack was needed – and Sydney’s MRT has the knowledge and hardware to achieve it.

Brett Middleton from MRT says this vehicle – owned by somebody who wishes to remain anonymous – has pretty well everything thrown at it.

“There’s a tick in every box,” says Brett.

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The call for maximum power and driveability meant ditching the 2.0 litre STi engine for a closed deck 2.5 litre US-spec STi block. Nothing like a 25 percent capacity increase to help things along! Custom MRT rods and forged pistons provide a static compression ratio of 8.0 - 8.5:1 – Brett says a compression ratio of at least 8.0:1 is required to maintain off-boost driveability. The entire engine has been balanced and blueprinted with the utmost attention to detail. A high capacity baffled sump protects the engine during sustained high-power runs.

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The cylinder heads can make or break Subaru engine performance so this car has a head package that flows heaps. The STi heads flow substantially better than WRX parts but when you treat the STi heads to an extensive port job and bigger valves, nothing comes close. The camshafts are custom MRT profiles which provide oomph from zero to hero. GFB pulleys enhance throttle response.

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The standard STi intake manifold provides plenty of airflow to go with the big cams and ported heads, but the stock exhaust manifold is replaced with an aftermarket unit. The turbo chosen for the job is a 450hp Garrett roller-bearing unit with an internal wastegate. A custom MRT splitter dump is bolted to the back of the turbo and feeds a 3 inch MRT exhaust. The intake to the turbo comprises a MRT silicone ‘under manifold’ pipe and Ram Pod.

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Compressed induction air is chilled by a custom MRT front-mount intercooler working in conjunction with a top-line Aquamist water injection system. Interestingly, an intercooler C02 spray was also about to be tested at the time of writing.

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Ninety-eight octane unleaded is squirted into the bores through a set of 650cc replacement injectors teamed with custom MRT fuel rails. A ‘500hp’ pump always has fuel available to it thanks to a MRT in-tank anti-surge pot.

The engine management is stock STi, though remapped to suit using EcuTeK software. Note that, as seen in this photo, a humungous 89mm ID airflow meter housing is employed (with airflow meter calibration altered via the EcuTeK program).

With this swag of mods, the big 2.5 litre flat-four has pushed out 356kW at the hubs on MRT's Dynapack dyno. Yep, that’s right - 356,000W at the hubs! This is achieved with boost pressure set in the high 20 psi range using a custom program in conjunction with a pneumatic bleed valve.

And what sort of driveline do you need to support an all-out 2.5 turbo?

A bloody serious one!

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The standard STi ‘box has been dropped to make way for a MRT close-ratio dog ‘box teamed with an extra heavy-duty twin-plate clutch. Traction is assured by aftermarket mechanical diffs front and rear. A high-torque 20 kg/m viscous coupling can also be found at the centre of the AWD system and, as discussed at Viscous Coupling Variations, this requires accompanying suspension mods to achieve balanced handling.

The car now has adjustable front and rear swaybars, alloy swaybar links, Whiteline Group 4 adjustable struts and MRT adjustable top hats at each end. Under-body bracing is also bolted under the nose. These suspension mods give the STi very neutral balance, while a set of semi-track tyres on Compomotive MO 17s provide glue-like adhesion.

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Brett says the car can accelerate to some truly breath-taking speeds – and you’ve gotta be able to wipe off that speed when you come to a corner. At the front you’ll find big Alcon calipers and 355mm DBA rotors mounted on custom aluminium hats. The rear uses 2-pot calipers and ventilated discs from a later model STi. A MRT brake master cylinder support bracket is also installed to provide improved feel and control in heavy braking.

The STi interior is equipped with a Cobra fixed back race seat (which is mounted on the original Subaru sliding rails) and a harness. A triple gauge pod is also mounted high on the dash – this is soon to be replaced by an EcuTeC in-car display, which gives data on all vital engine parameters.

At the time of writing, a roll cage was being installed under the recommendation of Brett Middleton.

“This car is now very quick on the track – I mean it’s really quick, so I suggested a roll cage be installed before the car goes onto the track again,” says Brett.

“But once the cage goes in I think we’ll be running out of things to do to the car – there’s nothing left to be done,” he says.

So it’s a case of goal achieved.

And then some.

Contact:

MRT Performance                                                          +61 2 9809 2110
                                                                                     www.mrtrally.com.au

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