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Rob
08-30-08, 07:42 AM
Corvette's biggest hammer: The LeMans-racing C6R

Henry Payne / The Detroit News
Saturday, August 30, 2008

The new 2009 ZR1, the fastest production Corvette ever made, draws on the marque's racing experience to allow this domesticated street steed to summon race car-like performance on the track.

Now meet the untamed beast in General Motors' stable.

In advance of today's American LeMans Series race at Belle Isle, Pratt & Miller -- the Milford-based company that runs GM's race program -- opened its facilities to journalists for a look at the Corvette C6R, the bright-yellow race car that has dominated the American LeMans GT-1 category and that will be the favorite to win its class again in Detroit this weekend.

Comparing the C6R and the ZR1, which I drove at GM's demanding Milford test track earlier this month (see "ZR1: For on and off the track" at right), shows what liberties engineers can take to make a competition car. But it also shows how much DNA the street able ZR1 shares with the premier GT racing car in the world today.

Per LeMans GT-class requirements, the C6R must be built off the same aluminum chassis as the production Vette. It also shares the same aluminum, 7-liter engine block as the ZO6 -- the ZR1's 505-horsepower, fiberglass-paneled cousin -- and its body profile must conform to the production template as well.

That's where the similarities end and the race modifications begin.

The ZR1's tidy engine bay sports a significant bulge where the supercharger sits atop its 6.2-liter, V-8 powerhouse. The normally-aspirated C6R's crown, by contrast, is enveloped by a massive black air box. Huge air ram tubes scale either side of the engine bay, feeding great gulps of air into the beast's lungs. While the C6R specs say the car makes 590 horsepower at 5,400 RPM -- compared to the ZR1's 638 -- the number is misleading.

Air restrictor rings choke the ram tubes where they enter the air box, regulating the amount of air -- and thus horsepower -- the engine gets. Remove the required restrictors and the Corvette could produce a staggering 1,000-plus horsepower at upwards of 8,000 RPM. Think of a modern NASCAR engine -- which shares the same lightweight, titanium drive train materials as the C6R and produces 900 horsepower with a 5.8-liter engine -- and you get some idea of the potential of an unchained C6R engine.

Public relations is synonymous with manufacturer-supported racing, and GM uses the C6R program to promote its commitment to E85 ethanol. In competition, the fuel doesn't compromise performance, but it does reduce efficiency as E85 does not go as far as a gallon of gas. As a result, race organizers allow the C6R to carry 28 gallons of fuel compared to 24 gallons for its gas competitors (both of which exceed the domesticated ZR1's 18-gallon tank).

And don't let the C6R's restricted horsepower numbers deceive. Stripped of the creature comforts found in the 3,350-pound ZR1's plush interior, the fiberglass-bodied C6R tips the scales at a mere 2,425 pounds. That improves to 4:1 the racing Vette's weight-to-power ratio as compared to the ZR1's already impressive 5:1 (most top street rods like the BMW M3 or Porsche 911 are 10:1).

Like the ZR1, the C6R stores its gearbox in the rear, guaranteeing 50-50 weight distribution, though Pratt & Miller's engineers actually add some ballast to the rear in order to bias balance to the rear wheels -- preferable in a front-engined car that operates at the very limits of adhesion.

And then there are those brakes.

The ZR1 is shoed with the same Brembo carbon-ceramic rotors that you'll find on exotics like the Ferrari Enzo, allowing the brakes to work at temperatures above the normal 1000 degrees Fahrenheit found with steel brake discs so that the big Vette can stop on a dime.

The C6R's AP Racing-supplied brakes go a step further. The race car's discs are made of pure carbon, allowing the brakes to operate at double the temperatures of steel rotors. Watch a C6R under braking at Belle Isle, and you'll see the rotors briefly glow orange. That means operating temperatures at a toasty 2000 degrees F!

But while the ZR1's ceramic composite construction provides immediate dispensation of heat, the C6R's surrounding materials (brake pads, calipers, ducts) must be constructed to meet the carbon brakes high heat -- meaning a price tag of $50,000 per brake assembly!

Throw on gummy Michelin slicks, rock-solid springs and shocks, a huge rear wing for downforce - then run the exhaust out the side of the car in order to free up the downforce-inducing diffuser tunnels behind the rear axles - and the C6R is ready to rumble.

Given its extensive Corvette racing experience, Pratt & Miller closely advised on the development of the 205-mph ZR1, says co-owner Gary Pratt. The result is a production car that deserves to share the C6R's stable.

twiget
08-30-08, 04:01 PM
Cool. I was beginning to wonder if the C6.R team played any role in the development of the ZR1. :confused I have read dozens of articles about the ZR1, and this is the first one that shows any link between the ZR1 and the C6.R

In contrast, one can hardly find a GM promo picture of the C6 Z06 with out a C6.R lurking somewhere it it. Or read an article about the Z06 with out the author mentioning the close ties the Z06 shares with the C6.R.

Jason