Corvette C6

Some critics believe the 2005 Chevrolet Corvette, or C6, is a rehashed 1997-04 C5. After researching the issue, we decided that, while not the departure from C5 that C5 was from the 1984-96 models, the 2005 Corvette really is different.

Only twice in its history has Corvette had a "normal" platform life cycle. The 1963-67 mid-year models lasted five years, while the 1997-04 C5 lasted eight. The 1953-62, 1968-82 and 1984-96 models were in production longer, and spawned vastly different successors. The '68 Vette was a new body on carry-over chassis, suspension and powertrain architecture. The '05 is somewhere between that and the '97, with a new body, upgraded chassis, new suspension and partially new powertrain.

New-for-C6 talking points: Fixed headlamps. 1960s/'70s Stingray influence. Five inches shorter and an inch narrower. Fifty more horsepower. Nicer interior. Cool new electronic gadgetry. A little bit lighter. New suspension. Goodyear "Gen3 EMTs"-18s in the front and 19s out back. 70% new, by parts count, and 85% new by weight.

Stingray and Raptor meet the C5

The definitive new-Corvette visual is the fixed headlamps. Some say they're Viperish or look like a Mazda, but to us, resemblance to other cars is obscure. When a designer sticks projector lights on a low, sloped front end, there aren't a lot of ways to style them if they're to work well. The C6's front may seem vaguely like other cars, but what we see is a refreshing change from 42 years of hidden headlamps.

Each headlamp assembly has a Xenon high-intensity-discharge (HID) projector low beam and a halogen-projector high beam, plus parking, turn signal and daytime running lamps, all under a polycarbonate lens. This makes a whopping 66% more light, a 25% wider beam, and gives C6 an effective "flash-to-pass" feature. Finally! Corvette has go-fast-in-the-dark lighting-a very useful improvement.

Leaks out of GM were that the 2005 model would be more influenced by past Corvettes. Indeed, the front looks as if chief designer Tom Peters took the best of C5, some of the C5-R endurance road racer and what we liked about the 1968-82 Stingrays, then styled C6 from the A-pillar forward. An egg-crate grille, more pointed nose, higher peaked fenders and a more trapezoidal-shaped hood all came from the 1968-82 design. The only feature that seems not to work well is the front fender vents-a little too edgy, perhaps; the C5's looked better.

From the side view, you see more 1968-82 Corvette in how the fender peaks extend onto the doors. The B-pillar and the hatch glass have obvious 1963-67-model lineage. Peters claims that the F22 Raptor fighter jet also influenced C6's side view.

The rear deck is sculpted with a slight dihedral shape. After 14 years of classic Chevrolet, round taillamps are back. Media information said, "Reflector optics give the taillamps a glow reminiscent of jet afterburners." That's Chevy spin-but we have to admit, the visual cue is pretty cool. Perhaps a result of C5-R aerodynamics work, a defuser panel, which carries reverse lights, is at the bottom of the rear fascia. In the middle of the defuser is the exhaust.

A controversial aspect of C5's exterior was its rear end. I liked the 1997-04 rear because it reminded me of early-1980s Corvette GTP racecars, but some people saw its styling as too wide. They will be happier with C6. While more visually complicated, it's not as wide.

Unfortunately, C5's quad exhaust is retained. We think Corvette exhaust should be two big pipes, not four little ones. A new exhaust system makes that an easy aftermarket change. From the back, you'll see the other exterior quirk: that strange mini-deck spoiler/CHMSL doodad. It is about a third of the car's width, and gray, regardless of body color. The first aftermarket C6 product will have those in body colors.

Tom Peters and his designers have done well in blending increased influence of past Corvettes, the theme set by the 1997 car, a little bit of the C5-Rs and some new ambiance into the 2005 model. The five-inch reduction in length and a 1.1-inch decrease in width makes the 2005 Corvette virtually the same size as a prime competitor, the Porsche 911.

The C6 rear suspension: Everything here is different, the most noticeable being the change in location of the rear spring from below to above the control arms.

Pop the Hood

Though C6's hood is not carbon fiber, which we expected after GM used it on some 2004 Z06's, it is smaller, lighter, stiffer and-thank you, Lord-it latches securely at a single position. No more running around to close the other side of a hood that didn't latch.

Corvette's 400hp, 6.0-liter (366-cu.in.) is the biggest, most powerful base engine in Corvette's 52-year history. Called LS2 and part of GM Powertrain (GMPT) Division's new Generation Four (Gen IV) Small-Block Engine family, it is derived from C5's Gen IIIs. Key features are: 50 more horsepower More torque: 40 lbs.-ft. more for automatics, 25 more for manual 6-speed 800 rpm higher power peak; 400 rpm higher torque peak New block with external knock sensor mounts and revised oiling Bore increased to 101.6mm (4.00 inches) Lower tension rings Full-floating wrist pins 10.9:1 compression Redesigned oil pan Higher-lift camshaft Camshaft sensor relocated to the rear of block Stronger timing chain New cylinder heads New valve springs Larger, 90mm throttle body Exhaust manifolds weigh 33% less and flow 4% better Reduced-mass water pump with improved sealing Iridium-tipped spark plugs More powerful engine controller incorporating all electronic throttle control functions 6,500-rpm red line No fuel economy loss despite increased power LS2s in Z51s get an engine oil cooler   The oiling system was revised and the camshaft and knock sensors moved to make room for Displacement on Demand (DoD) hydraulics. Corvette doesn't use DoD, yet, because of chassis resonance when the engine is running as a four-cylinder; but other Gen IVs will, so, in the interest of efficiency, all Gen IV aluminum blocks have the same oiling system. Eventually, Corvette may get DoD.

It's interesting that GM is trying low-tension piston rings, again. Early Gen IIIs had them, and some of those engines had oil consumption problems. An eventual service bulletin fix included a higher-tension oil-ring expander. It will be interesting to see how GM fares with low-tension rings, this time. The full-floating pins are said to reduce cold piston knock, but we think a more significant benefit will come in the durability of the 500hp LS7. Oops. Did we just let out a secret?

The new heads use the valve sizes and port configurations of the 2001-04 LS6. Interestingly, the six-liter Gen IV gets within 100 rpm of the LS6 without the LS6's hollow-stem valves-must be those new valve springs.

LS2 has two catalytic converters rather than four. Improved technology enabled GM to get rid of the pup cats used on base engines (since 2000 in California and 2001 nationwide) and the air-injection system. To hasten cat light-off, they're mounted close to the manifolds. The exhaust behind the cats is less restrictive. Better-flowing in-line mufflers replace C5's transverse mufflers. They eliminate unwanted noise, particularly between 1,500 and 2,400 rpm, with "tri-flow technology" (the nature of which was not explained) and larger volume. In terms of fuel efficiency, the LS2 gets 22.6 EPA-combined miles per gallon, making it more efficient than most of its competitors' engines.

The C6 front suspension: It all kind of looks the same, but nothing here interchanges with the C5.

Shifting Revisions

The Tremec T56 six-speed manual gearbox shifts more smoothly and precisely due to new linkage and shift-rail bearings inside the case. A shorter shift lever and synchronizers having 10% less travel shorten the shift throw. Manual-equipped cars ordered with the Z51 option get the lower 1st-4th gears used in 2001-04 Z06es, a taller fifth gear and a transmission cooler. The dreaded Computer Aided Gear Selection (CAGS) continues as a fuel-economy enhancement, but we've never understood the stress it causes. Drive properly, and CAGS rarely enables.

The C6 can also be equipped with GM's Hydra-Matic 4L65-E four-speed automatic transmission. Some media rumored it would share the Cadillac XLR's 5L50-E five-speed, but the 5L50 is not strong enough for the LS2's output. The L65 is a beefed-up 4L60-E, used from 1993 to 2004, and has the same gear ratios but higher input torque rating.

The key features of its higher capacity are: Input and reaction gear sets with five rather than four pinions Heat-treated stator shaft splines Induction-hardened turbine shaft Stronger low/reverse roller clutch assembly A seven-, rather than six-plate, 3-4 clutch Shot-peened output shaft Revised valve body and controller calibrations   The transmission calibration includes "Performance Algorithm Shifting." Chevy says, "This technology automatically selects the optimal gear for a given driving condition, making it a willing accomplice for performance driving and hard cornering." Sheesh, more spin. It's software which, using the C6's various sensors, anticipates the driver's actions and alters shift schedule accordingly. We'll have more on this when we test a C6 later this year. The L65's 380 lbs.-ft. input torque rating is less than the LS2's output, so we suspect its PCM applies torque management during WOT shifts at high rpm.

C5 rear-axle ratios carry over. Limited-slip differential pre-load was increased to improve handling on corner entries. The Z51s have a rear-axle cooler inside the transmission; axle lubricant is cooled by the transmission which is, in turn, cooled by the radiator-effective engineering, indeed.

Inside the C6

There are no handles or locks on a 2005 Corvette. Slide your fingers into a cavity at the upper rear of the door. Touch a switch on the inside of the door skin. The door pops ajar. The whole process is very cool. Dead battery? Turn the key in a hidden lock under the license plate and the hatch opens. In the cargo area is a pull cable that opens the driver's door.

The interior retains Corvette's classic "dual cockpit" layout, a tradition since 1963, but uses upgraded materials. The instrument panel and doors are covered with cast-in-place, semi-gloss, skinned foam. It is soft to the touch and looks like padded leather. GM claims it "...has twice the life of conventional automotive soft trim, resists fading and minimizes interior fogging, which occurs as plasticizers migrate out of the material."

When we first sat in a C6 last December, the interior seemed more spacious and looked brighter, more modern and less cluttered. Flush-fit radio and climate controls, their surrounding trim plates and the instrument panel-to-door closure gave that feeling. On the other hand, the steering wheel looked like it came from some other car, a curious choice in light of Chevrolet's stated goal of upgraded materials. Another thing I don't like? The passenger's grab bar is gone.

Power driver and manual passenger seats, both with manual recliners, are standard. Their construction, an aluminum base with a composite frame, carries from the C5. Hopefully, the recliner mechanism improves upon the C5's, which occasionally malfunctioned. Available Sport Seats have power recliner, lumbar and side bolsters, side-impact air bags and optional seat heaters. Truly good automotive seating is not obvious, until you're on the road. We'll pass on the final judgment of C6 seats until GM lets us drive one.

Analog instruments continue but are improved in execution. Idiot lights move from the tach and speedo faces to between them. All gauges are more legible and lit with white LEDs at all times, offering high contrast, even in sunlight. And the Head-Up Display (HUD) returns as an option but has been upgraded with a dot-matrix display and separate Street and Track modes. The latter displays lateral acceleration.

Convenience, entertainment and information electronics begin with a keyless entry system. Move close to a door with the key-fob in your pocket and they unlock. Once you're in, the engine starts, not with a key, but a button. All locking and security is accomplished electronically. We hope this system's reliability is better than was C5's sometimes troublesome steering-column lock.

Standard are AM-FM Stereo, CD player, MP3 capability and seven speakers. The mid-level system adds Bose speakers and a six-disc, in-dash CD changer. The up-level system adds a GPS navigation system but deletes the CD changer, because there's not enough space for both. The navigation system can display on the HUD. The XM satellite radio, Homelink and On-Star are also available. The C6 continues using hidden radio antennas like the C5 coupes and convertibles, which resulted in weak AM reception. Chevrolet claims new technology improves reception.

The lift-off roof has been redesigned. It is larger, for a more open-air feeling, but lighter, making it easier to remove and load in the back. While storage space in the cockpit increases, Chevy's specifications show cargo space decreasing by 2.2 cu.ft. Chevy also claims the car's downsizing was achieved "...with virtually no loss of usable space." Confused? So are we.

Clearly, some high-level GM executives drive fast while sucking down Slurpees because Chevrolet advised the media that the C6 offers "...two cup holders designed to handle the car's high lateral acceleration capability. Adequate stability for lateral and fore/aft acceleration was a top priority to keep two travel cups or 20-oz. bottles in place during performance driving maneuvers."

Chassis, Suspension and Brakes

The Sixth-Generation Corvette chassis retains key characteristics of the groundbreaking 1997 model: front engine, rear transaxle and low-mass/high-stiffness backbone structure. Hydroformed steel frame rails, steel driveline tunnel, steel bulkhead behind the seats, balsa-wood-cored composite floors and aluminum cockpit structure, continue in enhanced form for 2005.

The frame was shortened three inches in the front and two inches in the rear. The exterior redesign and better placement of energy-absorbing foam used to enhance crash-worthiness were also part of the shortening. For increased stiffness and weight reduction: 1) the tunnel bottom panel is now aluminum; 2) the cross-car instrument panel beam was reinforced; 3) the rear compartment tub was reinforced; 4) aluminum braces were added under the tub. The C6 suspension, though similar in configuration to C5, has no major carry-over parts. The redesign was driven by these goals: 1) improved ride and handling; 2) improved steering feel; 3) a 1.2-inch wheelbase stretch required by a longer transmission in other cars built off the GMX245 platform, the Cadillac XLR.

Improved ride is accomplished by: 1) increased suspension travel, 0.5 inches up front and 0.8 inches in rear; 2) shock valving, which takes advantage of that increased travel; 3) more compliant Goodyear Extended Mobility or "run-flat" tires (EMT).

While the first two are easy to understand, the new Goodyears need elaboration. For 1994-04, EMTs alone provided safe handling when low or flat, so they had stiff casings. The C6 relies partially on its Active Handling stability enhancement system, which goes into a more aggressive, safety-oriented mode when low or no tire pressure is detected. Since tires no longer provide 100% of the run-flat handling, the tire casings could be more compliant. The result is a softer, quieter ride and improved handling when the car is driven hard on tires at proper pressures. The Goodyear F1 GS-2 EMTs on the front (P245/40ZR18) are the same width as those on the C5. The P285/35ZR19-sized rear tires are a bit wider. A C5 owner's complaint was tire noise; the C6 not only has quieter tires but is said to have better acoustic insulation in the rear.

With the C6 steering, the goal was less trough wander, which drivers feel as a slight "pulling" along with a change in steering effort. Many people blame this on the brakes because they often feel it when braking on a troughed road.

"Trough wander can be reduced by increasing caster," Corvette ride-and-handling Engineer Mike Neal told us, "so we increased caster, but it's not as simple as just bumping up the adjustment. We had to change the front lower control arm mounts on the front suspension cradle, so the cradle is new, too. The control arm is different. The knuckle is different. Adding caster changes ride steer, so we had to reposition the steering rack, recalibrate its effort curve and add new tire rods. The other thing that helped us with trough wander is the improvement in run-flat tire technology."

There are two levels of C6 suspension, FE1 and FE3. This year's buzzwords for FE1 and FE3 are: Standard Suspension and Sport Suspension.

There are two shock absorber choices for FE1, base and F55 Magnetic Selective Ride Control (MR). Mike Neal told us that, while basic MR design and operation is unchanged, shocks for the C6 version are longer, to go with the increased ride travel, and there's a new Siemens controller with revised calibration. The MR technology was profiled in the Hemmings Muscle Machines issue #3 and on the Internet at: http://www.corvetteactioncenter.com/kb/question.php?qstId=503.

The Z51's Sport Suspension uses stiffer, 45mm diameter, fixed-valve, shocks vs. the non-F55, Standard Suspension's 36mm fixed-valve units. The Z51 also has higher-rate springs and stabilizer bars, a power steering cooler and, now, a specific tire. Goodyear combined some technology from the 2001-04 Z06's F1 Supercar non-run-flat tire with gen3-EMT features to make a F1 Supercar EMT. It has an asymmetrical tread and some compounding differences that add up to slightly better handling compared to FE1's EMT.

The most costly warranty issue with 1997-04 C5 Vettes was brakes. Base C6 rotors are the same diameter and thickness (12.8x1.26-in. front and 12.0x1.0-in. rear), but weigh 2 pounds more per rotor and have redesigned vents for improved cooling. The Z51s get new, larger rotors (13.4x1.26-in. and 13.0x1.0-in.) which will improve fade resistance under racetrack conditions.

All C6es, regardless of suspension level, handle better and are a bit easier to drive at the limit due to better run-flat tires, a slight increase in roll stiffness and changes in shock valving. What should the sporting C6 driver feel in comparison to the C5?

"More cornering power...that's the biggest thing," Mike Neal says. "And the second thing is more of 'combination traction,' which is, on the friction circle, both lateral and tractive grip. So, as you're powering out of a corner, you're not as quick to lose traction in the rear. The back stays hooked up better."

General Motors claims the 2005 Z51s can handle, brake and accelerate just this side of a 2004 Z06. If that is true, more than a few Z06s will get traded for 2005 Z51s.

Some Projections

1 How much? Chevrolet hasn't released MSRP, but we guess $44 to $45K.

2 When? Deliveries begin in late August or early September.

3 How will it perform? Considering that a manual Z51 weighs about 3,200 pounds, its transmission ratios, 50 more horsepower and better tires, we'll say it should run the quarter mile in 12.6 seconds at 115 mph. Chief engineer Dave Hill has said, "If the Z06 was four-seconds-a-lap faster than a base C5 (on an unidentified racetrack), the new Z51 takes back three of those seconds." Chevrolet claims a Z51 is capable of 0.95g lateral acceleration. As for top speed? With 400hp, a taller fifth gear and a .28 drag coefficient, a 2005 Corvette targa with a manual gearbox will top out around 180 mph. We think all this performance will come in a more refined and quieter manner.

Again, we'll reserve our final opinion until we drive the car-we're told that will be sometime in May-but the C6 Z51 looks like it'll be a hell of a ride.