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Gotcha: The "mystery GM prototype", as pictured in Autocar.

Autocar spies what could be a turbo Commodore as GM unveils 476kW/819Nm SV8

29 Apr 2008

RESPECTED British motoring magazine Autocar has published photographs on its website of a heavily disguised evaluation vehicle that appears to be either a Holden Commodore or a related model testing in Sweden.

Autocar claims the “mystery GM prototype” has several design cues that suggest a new Holden model lies underneath its cladding. It also reports that registration details confirm the car is a Holden, with the database attached to the licence plate indicating that the car is 4850mm long, 1800mm wide and weighs 1650kg. According to Autocar, it also has a 260bhp (194kW) engine paired with an automatic gearbox.

“If it is a Holden, Saab engineers could be working on either a four-wheel drive transmission, or on turbocharged petrol engine for the car. Saab is a centre of excellence within GM for both these areas of engineering,” Autocar said.

While GoAuto believes it is unlikely that a rear-drive Holden would be converted to all-wheel drive, despite the fact it may open up more sales in the US and Europe, there is a strong prospect of a large-capacity turbo V6 being developed for Commodore and export models. Holden already produces a 2.8-litre V6 at its Port Melbourne engine plant that is turbocharged for use in the Saab 9-3. Saab and Holden could now be involved in engineering a bigger version that would rival the upgraded inline turbo six that powers Ford Australia’s FG Falcon XR6 Turbo and G6E Turbo models.

Such an engine was previewed nearly four years ago at the 2004 Sydney motor show, where Holden revealed the TT36 'Torana' concept, powered by a twin-turbocharged 3.6-litre Alloytec V6 delivering 280kW and some 480Nm of torque. Ford's latest XR6T engine produces 270kW and 533Nm, while next month's new FPV version will produce 310kW and 551Nm.

The experimental V6 was hand-built at Holden's then-new engine plant at Port Melbourne, featured two KO4 Warner turbochargers and an air-to-air intercooler and, according to Holden, produced 90 per cent of peak torque from just 1600rpm.

137 center imageWhile the vehicle’s disguised styling could point to any number of Holden-developed GM vehicles – from Buick, Cadillac, Pontiac and perhaps even Saab – the prototype could also be testing other technology for export markets. Sweden is often used for electronic stability control calibration, for example.

Also of interest to Australian motoring enthusiasts is the release from General Motors last week of official performance figures for the supercharged 6.2-litre LS9 V8 that powers the Chevrolet Corvette ZR1 (pictured at left).

Providing the possible basis for a GTS model from Holden Special Vehicles, the LS9 produces a whopping 476kW of power and a phenomenal 819Nm of torque – figures that have come in above the original estimates given in January at the Detroit auto show, where the ZR1 was first shown.

Any engine that appears in the iconic Corvette gives rise to hope that it could be used by HSV. While there is no official word on whether Australia will see the LS9, the naturally-aspirated 6.2-litre LS3 engine that currently serves the standard Corvette powers HSV models from this month. Thanks to the supercharged LS9 engine, the Corvette ZR1 can achieve a top speed of more than 322km/h (200mph). It is intercooled and uses a Roots-type supercharger with a unique four-lobe rotor set-up that has been designed for quieter and more efficient performance. It has 2.3-litres of displacement to ensure adequate air volume at high engine speed and runs a maximum boost pressure of 10.5 psi (0.72 bar).

The LS9 also has a forged steel crankshaft with a nine-bolt flange, titanium con-rods, forged aluminium pistons, stronger rotocast cylinder-heads with custom titanium intake valves and hollow-stem, sodium-filled exhaust valves.

GM has also developed a special camshaft developed for excellent idle and low-speed driving characteristics, a 9.9-litre dry-sump oiling system with integrated oil-cooler and piston-cooling oil squirters.

Of course, customers will never get to see any of this unless something goes horribly wrong, so Chevrolet has given the outside of the LS9 engine a unique look. Its intercooler cover, which is visible through the bonnet, is painted blue and has LS9 Supercharged stamped on it.

While you might expect the ZR1 Corvette fitted with a blown V8 would be a rumbling, grumbling monster, Chevrolet general manager Ed Peper insists it is a refined machine.

“One of the most amazing things about the Corvette ZR1 is the level of refinement that our designers and engineers have attained,” he said. “Even with all that power, this car has road manners that will allow our customers to enjoy it on the streets as a daily driver, and on the track.”

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