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.
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.
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
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.
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.
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
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
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!
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.
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.
+61 2 9809 2110