Auto Car Magazine: Corvette Z06 in Depth (Europe)

Saturday, December 29, 2007

Corvette Z06 in Depth (Europe)

Page 1: Summary
Page 2: Exterior / Interior
Page 3: Performance
Page 4: Body Structure / Chassis
Page 5: Born on the Track
Page 6: Specifications

Performance and efficiency

With 377 kW (512 DIN horsepower) and 637 Nm of torque the 7-liter LS7 engine powering the Corvette Z06 is the most powerful passenger car engine ever produced by GM. The engine is also designed to rev to an unprecedented 7000 rpm limit.

Easily identified under the hood by red engine covers with black lettering, the LS7 engine powering the Corvette Z06 delivers 377 kW (512 DIN horsepower) at 6300 rpm and 637 Nm of torque at 4800 rpm. In a 1418 kg package, that gives first gear 0-100 km/h acceleration in 3.9 seconds and a top speed of 320 km/h.

Unlike the previous 427 cubic inch (6997 cm³) engine, which was a big-block design, the 7.0-liter LS7 is a small-block V-8, the largest-displacement small-block ever produced by GM and a tribute to its 50 years as a performance icon. The LS7 shares the same basic Gen IV V-8 architecture as the Corvette’s 6.0-liter LS2, but it uses a unique cylinder block casting with large, 104.8 mm bores and pressed-in cylinder liners for the 101.6 mm stroke. Compared with the LS2, the LS7 also has a different front cover, oil pan, exhaust manifolds and cylinder heads – among many other components.

Race-bred technology

One of the clearest examples of the LS7’s race-bred technology is its use of titanium connecting rods. They weigh just 480 grams a piece, almost 30 percent less than the rods in the LS2 V-8. Besides being light in weight, which reduces loadings, enhancing high-rpm performance and rpm range, titanium also makes the rods extremely durable.

The LS7’s specifications also include an 11.0:1 compression ratio, a high-lift camshaft, a forged steel crankshaft; forged aluminium flat-top pistons; racing-derived CNC-ported aluminium cylinder heads with titanium intake valves and sodium-filled exhaust valves and titanium pushrods and valve springs.

The LS7’s CNC-ported aluminum cylinder heads are all-new and designed to meet the high airflow demands of the engine’s 7.0-liter displacement, as it ingests approximately 100 cubic feet more air per minute than the regular Corvette’s 6.0-liter V-8, an 18-percent increase in airflow.

Optimal, uninterrupted airflow

To ensure optimal, uninterrupted airflow, the LS7’s heads have straight, tunnel-like intake runners. Very large by production-vehicle standards – even racing standards – they are designed to maintain fast airflow velocity, providing excellent torque at low rpm and exhilarating horsepower at high rpm. The heads feature 70-cm³ combustion chambers that are fed by huge, 56 mm-diameter titanium intake valves.

They are complemented by 41 mm sodium-filled exhaust valves, compared with 39.4 mm valves in the LS2. To accommodate the large valve face diameters, the heads’ valve seats are siamesed; and, taken from experience with the engines of C5-R racecars, the LS7’s valve angles are held at 12 degrees, compared with 15 degrees for the LS2, to enhance airflow through the ports.

The exhaust gases flow through light weight, four-into-one headers to new, close-coupled catalytic converters and through to new ‘bi-modal’ mufflers. The mufflers each feature a vacuum-actuated outlet valve, which controls exhaust noise during low-load operation but opens for maximum power.

All LS7 engines are assembled by hand at GM Powertrain’s Performance Build Center in Wixom, Michigan. The exacting standards to which they are built include deck-plate honing of the cylinders – a procedure normally associated with the building of racing engines and almost unheard of in a production-vehicle engine.

Dry-sump lubrication system

The LS7 engine has a dry-sump lubrication system designed to keep the engine fully lubricated during the high cornering loads the Corvette Z06 is capable of producing. An engine compartment-mounted reservoir delivers oil at a constant pressure to an oil pump pick-up at the bottom of the engine. The pressurized oil feed keeps the oil pick-up continually immersed in oil at cornering loads exceeding 1 g.

The LS7’s dry-sump system was developed and tested on racetracks in the United States and Europe, including Germany’s famed Nürburgring Nordschleife (which the Corvette Z06 lapped in 7 minutes 43 seconds). While common in racing cars, the Z06 is one of just a handful of production vehicles, and the only production Corvette, to incorporate such a high-performance lubrication system.

At the rear of the LS7 engine, a single-mass flywheel and lightweight, high-capacity clutch channel torque to the rear-mounted ‘transaxle’ which has been strengthened to handle the LS7’s increased torque load. The transmission includes a pump which sends transmission fluid to the front radiator for cooling. Upon its return, the fluid removes additional heat from the differential before returning to the transmission.

The six-speed manual transmission, rear mounted for optimum weight distribution and traction, connects to a limited-slip differential, with enlarged ring and pinion gears. Stronger axle half-shafts with tougher universal joints transmit power to the rear wheels.

“In many ways, the LS7 is a racing engine in a street car,” said Dave Muscaro, assistant chief engineer of small-block V-8 for GM passenger cars. “We’ve taken much of what we’ve learned over the years from the 7.0-liter Corvette racing program and instilled it here. There really has been nothing else like it offered in a GM production vehicle.”

Surprising efficiency

While the performance of the LS7 engine in the Corvette Z06 is undoubtedly stunning, its efficiency too, has created an interesting postscript. In the USA, an Energy Tax Act of 1998 established a ‘Gas Guzzler Tax’ on the sale of new model year vehicles whose fuel economy fails to meet certain statutory levels. The gas guzzler tax applies only to cars (not trucks) and is collected by the IRS, based on a combined fuel economy MPG value (55% city, 45% highway), used to determine tax liability.

Any vehicle which can achieve a calculated combined fuel economy level of at least 22.5 mpg (10.4 l/100 km) is unpenalized. Vehicles which fall below this are taxed on a sliding scale, beginning with a surcharge on the new car price of $ 1000, and increasing to $ 7,700.

Both the Corvette, which achieves a calculated 25.1 mpg (9.37 l/100 km) and the Corvette Z06 which achieves 22.7 mpg (10.36 l/100 km) meet these requirements and avoid the tax. No other 500 hp car (nor 400 hp car for that matter) can match this efficiency.