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ZR1 is back, with 800Nm on tap

2007-12-21 08:50
Vehicle Specs
Manufacturer Chevrolet
Model Corvette ZR1
Engine 6.2-litre V8, supercharged
Power 462kW @ 6500r/min (projected)
Torque 807Nm @ 4000r/min
Transmission Six-speed manual
The quintessential American supercar, Chevrolet's Corvette, is reviving the notorious ZR1 moniker thanks to some Eaton assisted supercharging trickery.

The ZR1 will feature carbon-ceramic brake rotors, carbon-fiber body components and the venerable small block Chevrolet V8.

This legendary Chevrolet engine which has morphed from 5.7- to 6.2-litres in the Corvette application over the years.

Corvette engineers have decided belt-driven forced induction, instead of exhaust driven turbocharging, was the ticket to outlandish power output.

Brandishing the legendary ZR1 moniker, this supercharged 'Vette is to be launched midway through 2008.

Charged and guilty

Legendary supercharger manufacturer Eaton supplied a model R2300 design 'blower' for the Corvette ZR1. This large, positive-displacement Roots-type supercharger - with a unique four-lobe design - was developed specifically for the ZR1 by Eaton.

With engine displacement already a substantial 6.2-litres, packaging all the extra performance 'plumbing' under the bonnet was a significant engineering challenge for the project.

Especially the special liquid-to-air cooling system which facilitates lower air inlet temperature and provides cooler, denser air for optimal combustion, was a unique packaging challenge.

Subsequently the charge cooler was designed as a 'dual brick' system, with a pair of low-profile heat exchangers mounted longitudinally on either side of the supercharger.

Coupled with the supercharger itself, this integrated design mounts to the engine in place of a conventional intake manifold and is only slightly taller than a non-supercharged 6.2L engine.

The rest of the engine is still a curious mix of contemporary and traditional.

It features an aluminium block and aluminium alloy heads, with anarchic pushrod driven titanium intake and sodium-filled exhaust valves are used for their lightweight and high-rpm capability, and dry-sump lubrication. Swirl-inducing wings are cast into the intake ports to improving motion of the air/fuel mixture flow.

Aiming for 800Nm

Featuring vast swept capacity and supercharging a synergy in power output has been the primary goal of the ZR1 project.

Although final SAE power levels are only set for release in March of 2008, the ZR1 supercharged small-block V8 has already managed to push 424Nm of torque at only 1000r/min on the test bench and 224kW at 3000r/min.

Peak power targets are 807Nm at 4000r/min and 462kW at 6500r/min by March 2008. The ZR1 project team are confident of achieving these figures.

Although pushrod engines are notoriously unhappy at high revs, with peak power set for 6500/rmin and using the standard Corvette 7100/rmin redline, Corvette engineers are pushing the limits of this vale-gear application. As Tom Stephens, GM group vice president for powertrain and quality says,"We haven't yet realised the small-block's performance potential."

To put these power figures in perspective the current ace Z06 Corvette is a race-inspired 7.0-litre V8 job producing 377 kW at 6 300 r/min and peak torque of 637 Nm at 4 800 r/min.

These performance credentials allow the current quickest 'Vette to sprint from 0 - 100 km/h in under four seconds and hit a top speed of 319 km/h. The mind boggles at how quick the ZR1 will actually be.

Extra strength

Considering the strain these projected final power figures will generate on the various ZR1 drivetrain components some toughening up of certain components was always going to be necessary.

Although the pistons are aluminium and the crankshaft is forged steel, the former to enable lower inertia and the latter to provide strength, the connecting rods, bearing much of the strain, are titanium. The heavy duty steel crankshaft features a nine-bolt flange instead of the standard Corvette six-bolt arrangement to keep everything together under maximum rotational force.

Beyond the engine the other drivetrain partner, a Tremec TR6060 six-speed manual gearbox with a twin plate clutch, necessitated its own special features to cope with the ZR1 power and torque outputs.

Featuring a twin-plate clutch with relatively small 260mm discs (standard 'Vettes have 290mm) has helped lower disc inertia and yielded much lower shift and clutch engagement effort. This should make the ZR1 less intimidating to drive in at low speed in urban areas.

ZR1-specific gearing includes a tall first gear to launch the manic big-daddy Corvette and a sixth gear has been profiled as an active dynamic ratio. ZR1 achieves top speed in sixth, instead of fifth, subsequently ZR1 sixth gear is not a traditional 'Vette type highway cruising ratio.

The ZR1's suspension design will be the same as in other Corvettes, but its front and rear stabilizer bars will be thicker.

By making Magnetic Selective Ride Control standard, Chevrolet engineers were able to fit the ZR1 with front and rear springs that are slightly softer than those of the Z06.

The wheels and tyres will be larger. It will have P285/30ZR19 front and P335/25ZR20 rear Michelin Pilot Sport 2 tires on 20-spoke alloy wheels. The 2009 ZR1 has a notorious reputation to live up to. The original ZR1, launched in 1989, was fettled by then GM owned Lotus.

It featured an aluminum-block V-8 with the same bore centers as the rest of the C4 'Vettes, but featured four overhead camshafts and 32 valves - something of an anomaly in Corvette history. By the end of its production run in 1995 it produced 300kW.


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