Subaru Oz’s new motorsport division was given the role of converting the brand’s hard-earned rally reputation into ballistic Impreza STi Spec Cs for the cashed-up Joe Average.
This feature was originally published in MOTOR’s April 2007 issue
The Aussie-designed and crafted Factory Tarmac version on the pages before you is its flagship head-kicker, and by far the wildest customer STi to date. Based on the FIA homologated Spec C ‘stripper’ Impreza, the 262kW/568Nm hand-built weapon is proof that Subaru’s accumulated rally experience can be transformed into turn-key practice when no expense is spared. How much expense exactly? Yours for a frosty $180,000.
The catch? Well, it’s not eligible for normal road registration. Instead, this is the full FIA Group N Tarmac spec monty, qualifying only for limited use rally rego. So if CAMS road rallies, targa events, hill climbs, etc are your bag…
In the hot seat
First thing is stripping out weight and getting down to essentials so the Spec C donor car comes without air-con, airbags or radio/CD. Subaru then turfs the seats, carpet and interior trim, and installs two Racetech Viper one-piece buckets, cage-mounted five-point harnesses and a Sparco racing tiller.
The dash pad is Alcantara, and door trims are moulded carbonfibre. Complementary mod cons include two fire extinguishers, a first aid kit, a tow rope, a Hitachi wheel nut rattle gun, and ‘natural’ air-conditioning provided via a carbon fibre roof vent.
The roll cage, developed by Possum Bourne Motor Sport and Aussie-based CONCENTRIC Asia Pacific, is a work of art. Designed with leading edge CATIA 3D computer modelling (used in Formula One, V8 Supercars, et al), it takes 120 hours to weld it in, extends to all four upper suspension mounting points for supreme structural rigidity, and fits tightly against the body shell inside the cabin.
Made from super-strong chrome-moly steel, it’s claimed to be the strongest FIA-accredited roll cage to date.
The six-speeder is a close-ratio synchromesh unit, with an option of dog-engagement gears from the gravel models’ five-cog unit. The regular MY07 STI driver-adjustable electric/mechanical centre diff remains, but uses a special Subaru controller module developed by MoTeC to vary front-to-rear torque split.
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The stock helical-type front LSD is replaced with a PBMS-tuned clutch-type unit, as used at the rear LSD. Heavy duty driveshafts, a solid-centre clutch, beefier driveline mounts, bracings and bushes make up the package.
Tipping the scales
At 1390kg, the Spec C is 105kg lighter than the regular STI, thanks to an aluminium bonnet and boot lid, a thinner roof panel, and lighter glass. Complete, the full-fruit Factory Tarmac is 1360kg.
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It’s built to international Group N Tarmac rules and is loaded with carbon fibre goodies such as the rear bulkhead, footwells, and mirrors – an extra $20,000 cost. Subaru Oz will supply a version for Aussie production car racing regs without carbon fibre bits, for a price of $160,000. Sump and fuel tank skid plates come standard.
Labour of love
Each Factory Tarmac arrives as a Spec C at Subaru Motorsport’s workshop. It takes 24 hours to strip to a bare shell, which is mounted on a rotating ‘spit’. Then there’s 12 hours of prep work (removing body sealer, tidying up the shell, et al), 40 hours of welding for strength, 120 hours for roll cage integration, and 100 hours of assembly. There’s 320 hours total labour invested in the shell and body alone.
$180,000 too rich for you? Subaru Motorsport has an entry-level Spec C base model (includes roll cage, seats, extinguisher) from $69,990, a mid-spec $87,990 Tarmac (adds Motec engine tuning, suspension), and a $125,990 National Tarmac (adds engine blueprint and further suspension work).
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Prefer dirtier fun? There’s also a club/state-level competition Gravel Rally package for $92,990, a more hard-core $128,990 National Rally version, and a full-combat, range-topping $195,000 PWRC monster ready for international Group N competition. All you need to add are brave pills.
Instead of the current STI 2.5-litre boxer four, the Spec C uses a 2.0-litre unit currently homologated for FIA Group N and WRC rallying. But this isn’t the old pre-MY06 engine. Instead, it shares much of its design with the current MY07 2.5, including the latest variable camshaft technology. The Spec C also comes with trick extractors and an exclusive, competition-type twin-scroll turbo.
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Subaru Motorsport spends 60 hours blueprinting the engine to optimise the standard engine’s tolerances. Exhaust is a PBMS design made of stainless steel.
Each boxer four then spends eight hours on an engine dyno; four for initial run-in and four for race-tuning using PBMS programming via the engine’s new MoTeC ECM. The result? 262kW/568Nm on racing fuel. Subaru says that it’s a conservative tune, and you can easily get up to 300kW. If you wanted to.
The Factory Tarmac’s no-more-to-spend package includes a Coralba C900 race computer and Peltor FMT200 intercom system for driver/co-driver in-helmet communication. These, the battery isolation switch and MoTeC diff and ECM mapping controllers are all controlled via the centre console and wired using a PBMS loom.
Tucked behind the lightweight 18-inch front alloys are monstrous AP Racing four-piston calipers with two-piece discs, with smaller four-potters in the rear. Plumbed with stainless steel lines, the stoppers are worth $15,000. Handbrake is a rally-style hydraulic unit.
Suspension is a combination of Aussie-made King Springs, Reiger dampers from Holland, larger STI swaybars and pillowball-type lateral links and trailing links for added sharpness.
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2007 Subaru Impreza STi Spec C
BODY: 4-door, 2-seat sedan
ENGINE: 1994cc 4cyl boxer DOHC 16v
BORE/STROKE: 92.0mm x 75.0mm
POWER: 262kW @ 4800rpm
TORQUE: 568Nm @ 3800rpm
TRANSMISSION: six-speed manual
SUSPENSION: Inverted type MacPherson strut, coil springs, anti-roll bar (f), inverted type dual-link, coil springs, anti-roll bar (r)
BRAKES: AP Racing 4-pot calipers front/rear, competition rotors, hydraulic handbrake
WHEELS: OZ Racing STI 18-inch
TYRES: Pirelli P-Zero, 235/40 ZR18
PRICE: $160,000 ($180,000 as tested)