MRT - MRT's STi article

Reproduced here with kind permission from www.AUTOSPEED.com.au
Words by Michael Knowling, Pix by Michael Knowling and MRT

We take a look at Brett Middleton's latest Group A rally weapon - a 1998 STi Impreza.

Brett Middleton (the owner of Sydney's Middleton Rally Team) has been doing "the business" in the dust and dirt of the Australian Rally Championship for nearly 20 years. His first competition vehicle - a Datsun 1600 - "didn't set the world on fire" but it did get him hooked on rally action. Hankering for a newer (and therefore more competitive) car, the Datto was then superseded by a 1.3 litre G102 Daihatsu Charade in around 1990. Following this, Brett opened his Ryde (Sydney) performance workshop - with a heavy focus on Daihatsu modification - and swapped over to the much meaner 1.6 Charade. Both of these ultra-reliable little hatches competed very successfully in the front wheel drive Formula 2 category, netting both class wins and championship victories.

Between 1997 and 2000, Brett contested in a Honda Civic VTi-R (which was also in the front-wheel-drive Formula 2 category). The Honda won its F2 debut year, but it became increasing difficult to compete with the increasing number of (more modified) kit cars. By the time 1999 rolled past, however, Subaru Impreza WRXs had earned an extraordinary rallying status (and cult following) - and Brett simply had to have one. The anticipated move to the all-wheel-drive WRX obviously meant a change in category - but Brett was more than prepared to mix it up with the "big boys" of Group A. Not surprisingly, the decision to jump into a Rex was also helped by the fact that his workshop had started specialising in the performance tuning of WRXs. So they knew the Scooby back to front.

After initially contemplating building up their own Group A car from scratch, the team made a suck-it-and-see offer on an already prepared (and rallied) Impreza STi Version 4. Much to their delight - and with some assistance from Subaru Australia - they scored it.

Group A Impreza STi...

Assembled by STi Japan in 1998, this built-for-rally Impreza enabled Toshihiro Arai to compete in that year's API Rally Australia. Unfortunately, however, the car's first competitive outing saw engine failure crippling it on only Special Stage 8.

The next time that this STi fired into competition, it was wearing Possum Bourne Motorsport livery and being driven by young-gun Cody Crocker in the 1999 Australian Group N Championship. This time it was much more successful, as Cody and his co-driver (Greg Foletta) claimed outright victory in the Group N championship.

And here's where Brett Middleton took up ownership...

Today, the Version 4 Impreza shell is still pretty well as it left the STi Japan workshop. Note, however, Brett has recently dressed it up with a Version 5 bonnet, grille and rear wing to give it an updated look. Amongst the stickers, you may also notice those cute carbon fibre mirrors and roof vent poking out. Inside, it's just the bare essentials - skeleton trim. Essential for rallying, however, are gauges for gearbox temperature, boost and oil pressure, Coralba navigation equipment, Momo wheel and Momo Kevlar/carbon seats. Carbon fibre interior windscreen vents also serve to maintain a low mass. Brett says you have to be "anal" when it comes to keeping weight down - every bolt on his STi has been cut to length or changed to alloy to shed every last gram!

When it comes to occupant safety, Brett and his co-driver (the highly experienced Andrew Benefield) are protected by a Possum Bourne Motorsport enhanced STi chrome-moly roll cage and a Lifeline on-board fire extinguisher system.

Under the scoop'd and vent'd aluminium hood is the trusty EJ20 flat four turbo - substantially trimmed in maximum power thanks to a mandatory 34mm intake restrictor. Dusty induction air is filtered through a MRT Group A Ram-pod, which is complimented by a high-temp, high-flow silicone hose set. At present, the car is running a (relatively small) specially modified IHI VF24 roller bearing turbocharger. Exiting the compressor is a boost curve that's mostly dictated by engine rpm and intake air temperature. Having the restrictor in place means airflow capacity drops off over about 4500 rpm - so there's not much point in trying to force in more (extra-heated) air. A maximum of around 20 psi can be seen under load at very low rpm.

The top-mount intercooler is standard Version 4 augmented by a MRT water spray. This incorporates a large water tank in the position of the OE fuel tank (around 40 litres capacity), a high pressure pump and twin (bored-out) STi spray nozzles. The system is heavily relied upon in competition, with water consumed at a rate of approximately 1 litre every 4 kilometres.

Coming direct from NZ's Possum Bourne Motorsport, it makes sense that the car runs a Possum Link ECU (complete with anti-lag function). The engine rev limit is set at 7500 rpm, but the restrictor-induced drop in torque over about 6500 makes revving the engine that hard pointless. Brett performed some of his own tuning before the commencement of the car's 2000 debut. Interestingly, he says he prefers to tune the ECU "on the fly", rather than on a chassis dyno. "It's more real," he adds. Note that MRT have also performed a "must do" fuel rail mod to prevent cylinder #3 going lean. This involves changing the pressure regulator and redirecting fuel from one rail to the other.

Other engine mods allowed under Group A regulations include GFB underdrive pulleys and a TurboSmart Type 2 blow-off valve (complete with a foam filter on the outlet). An upgraded MRT custom exhaust (with no cat converter but a hand-made wastegate/turbine dump pipe divider and a straight through rear muffler) spills the EJ20's wastage with a minimum of backpressure. Brett says a cat may soon be a requirement for Australian Group A competition.

Internally, the motor is 100% stock - to comply with Group N regulations. Note that this rally-prep'd STi already comes set-up with increased oil pressure to reduce the chance of bearing failure. However, after more than a full season of competition, the motor is now ready for a Group A-spec rebuild, and a new engine is being prepared for the next event. This will include such items as a revised compression ratio, gas rings, custom valves and different cams (all within Group A regulations). The exact complexion of the engine will depend on whether or not premium unleaded is introduced as the control fuel, rather than the current avgas. In Brett's car, avgas is contained in an in-boot fuel cell.

The rally car driveline uses a MRT 4-button clutch and billet flywheel, close-ratio MRT dog box (with an external oil cooler), an upgraded 20kg/m centre viscous coupling plus mechanical front and rear diffs. These were previously spinning a 4.4:1 ratio, but taller 4.1:1 gears were fitted because they are stronger. Note that the rear-end is also of the stronger Version 5 R180 variety, which incorporates thicker driveshafts, bigger brakes, stronger hubs and differential unit. Standard WRXs use a lighter-duty R160 rear-end.

With all this torque and traction flinging the fully fuelled and watered 1350kg Impreza down narrow dirt tracks, a powerful set of brakes is mandatory - not under Group A regulations, but in the name of personal longevity! Brett's STi uses a hybrid braking system. Up front are 4-pot STi calipers with ventilated DBA 2-piece alloy-hat slotted discs, while at the rear are Version 5 twin-pot STi calipers and discs. These are part of the Version 5 rear-end conversion. Anti-lock braking assistance is not fitted, and Brett (usually) elects to run Pagid RS14 pads. Interestingly, the handbrake is left standard, because it's impossible to lock the rear wheels when the heavy-duty 20kg/m diff is in use.

Brett suggests that with recent changes in Australian rallying, it's now more important than ever to have good handling. "A lot of people have near-identical power, so you try to get a speed advantage through superior handling." Brett employs Drummond Motor Sport 60mm Super Struts (featuring adjustable bump and rebound rates, plus hydraulic bump stops), a front anti-lift kit and Group N bushes throughout. The STi already comes with alloy front lower arms, and the standard swaybars are retained. Fifteen-inch Compomotive alloys allow Brett to run relatively high profile (65 series) rubber. The brand of choice is Falken, with "closed" and "open" treads used for different conditions. Tyre width varies between 195 and 205 (215s are presently being tested).

Just out of curiosity, we asked Brett how much would a car like this would sell for. He said it's hard to say, but somewhere around AUS$60,000-100,000. (So keep saving your pennies!)

Driving

Coming from a rear-wheel-drive Datsun 1600, front-drive Charades and a Honda, it's interesting to hear Brett admit that the AWD STi took a lot of getting used to. "It was a steep learning curve for me," he tells, "it handles corners totally different to the F2 cars." Prior to competition in the 2000 season, Brett squeezed in some last-minute test drives and was amazed at how well the Impreza could soak up rough terrain. However, he says the car is also very sensitive to ride height adjustment. In Perth last year - the car's very first event - the team experienced no less than five flat tyres because the suspension was set-up incorrect. "The car was so sideways it just kept puncturing the sidewalls," he ruefully remembers.

The STi rally car has no heavy under- or oversteer, because - as Brett says - the teams sets the car up prior to any particular event. Turn-in is always quick thanks to the STi quick-rack steering (complete with an upgraded pump). Throttle inputs are essential for altering the car's attitude, and Brett has maximised this response with several techniques; the engine runs "heaps of advance on light and medium loads", a relatively small turbocharger, blow-off valve and anti-lag. The teaming of a blow-off valve and anti-lag is said to work very well - the blow-off valve prevents the turbo stalling when the throttle is snapped shut, and the AL brings boost up ready for the next throttle application.

Response and a strong spread of low-to-mid-range torque is indeed what this car is all about. In terms of straightline grunt, Brett confesses that a road WRX with typical exhaust, intake, boost, VF22 and front-mount intercooler mods will run away from his rally car.

So how well does the MRT STi fare in competition?

Well, after a couple of rounds that taught Brett and the team a lot about setting the car up, things were starting to settle into place. Brett was feeling comfortable behind the wheel and was starting to climb in speed - until an abrupt end... The Falken Rally of Queensland saw Brett clip an embankment at high speed (while in 5th position outright) and spear off-course into a tree. The damage can be seen in this photo - it resulted in a smashed camshaft bank, bent tailshaft, cracked gearbox and bent rear crossmember. Not long after this, the STi again come unstuck in Coffs Harbour. While in 6th place (outright) Brett unfortunately rolled 2½ times - through a patch of lantana bushes. Thankfully, the damage was quite minimal - testament to the strength of the comprehensive roll cage. (The lantana wasn't so lucky.)

Since then, however, things have been humming along very smoothly. Brett is now at home in the STi and starting to perform better in the Group A class. A string of strong finishes placed Brett 3rd outright in last year's Group A class - beaten only by the WRC cars of Possum Bourne and Neil Bates. Brett says he'll always be aiming to dominate the privateer group - at minimum.

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