If Corvette chief engineer Tadge Juechter said “Corvette is the poster child for continuous improvement. Making our car look, feel and perform better is what we do every day.”

“Last year, we added a premium steering gear in response to owners who felt that Corvettes could benefit from improved on-center feel and precision,” adds Juechter.

For 2009, we found another means of making Corvette steering even better.
Quicker steering ratios make a car feel nimble and responsive. But if the ratio is too quick, the car is nervous at highway speeds. Juechter’s ‘even better’ development is a variable-ratio rack-and-pinion steering gear that provides the best of both worlds.

Terrel Johnson, a Corvette engineering team member for five years, is the lead steering design engineer.

Johnson explains:

“The new variable-ratio steering provides the same 17.1 to 1 on-center ratio that we’ve used successfully for years. But when the steering wheel angle exceeds 15 degrees of left or right turning, the ratio begins speeding up.
The change is so gradual that the driver notices nothing unusual, but after a little more than half a turn of the steering wheel, the ratio has changed to 14.6 to 1. This trims the number of turns lock-to-lock from 2.78 to only 2.54, a 9-percent improvement.

“With multiple ratios in one steering gear, we’re able to tune the on-center zone for excellent stability and reduced sensitivity at highway speeds without making Corvettes feel sluggish around town. The quicker off-center ratio helps the car feel more nimble and highly maneuverable while parking or negotiating a U-turn.”

Asked exactly how the variable-ratio gearing is achieved, Johnson answered with two words: helix angles. Some digging revealed what he was talking about.

Inside the rack-and-pinion steering system, the pinion gear teeth encircle their shaft in a spiral called a helix. This configuration increases the number of pinion teeth in contact with rack teeth.
The greater the gear-to-gear contact area (more teeth engaged), the less the likelihood of lash when the rack-and-pinion assembly is under load. Lash is steering precision’s bitter enemy.

Pinion gear teeth must be evenly spaced because each tooth contacts the rack at least twice during the two-plus turns lock-to-lock.
But, since each rack tooth is engaged only once throughout the rack’s full travel, how the rack teeth are configured can vary.

At the center of the steering rack, the teeth are cut at a 14-degree helix angle. This causes the rack teeth to engage the pinion teeth at their roots, yielding minimal rack motion for each increment of pinion rotation.

At the end of the rack, the teeth are cut at an 18-degree helix angle. Now the rack teeth engage the pinion gear teeth near their outmost tips. That larger-radius point of contact causes the rack to move substantially more for each increment of pinion rotation. Presto: a faster steering ratio.

Variable-ratio steering is another example of a seemingly miniscule change that yields a noticeable improvement in the Corvette’s daily-driving behavior.

From the engineer’s perspective, the Corvette is a Rubik’s cube of interlocking, interacting systems.
A small change here can inflict major consequences there. Corralling an additional 36 horses under the hood for 2008 sent transmission engineers scurrying to make sure their chunks of the cube could take the gaff.

Design release engineer Dave Howe, who’s responsible for the Corvette’s six-speed manual transaxle, explains, “Our objective was to provide the necessary torque capacity without major disturbances to the basic design. But while we were at it, we seized the opportunity to install improvements every customer will appreciate.”

Changes for 2008 included wider gears for increased torque capacity, higher-capacity synchronizers, finer splines and machined teeth for the dog clutches, and new single-piece (replacing two-piece) shift forks.
For increased stiffness at the front of the transmission, the oil-circulating pump has been moved inside the case and its flow rate has been increased by 15 percent.

Various ribs, reinforcements and flange thicknesses are increased, and the countershaft is a new, more robust single-piece (versus two-piece) design. Differential ring and pinion gears are now shot-peened twice for enhanced durability, and the span between their support bearings has been increased to the Z06 dimension.

When the chips settled, Howe and his platoon of colleagues had altered over 90 percent of the Corvette’s six-speed manual transmission’s components.
That prompted a new TR-6060 identification label to supersede the previous T-56 nameplate.
Validation testing proved that all the attention was warranted. The new gearbox is not only tough enough to stand up to the LS3 V8’s ferocity, it’s also slicker-shifting with a 10-percent reduction in motion and effort.

Across the hall at GM Powertrain, the engineers responsible for the Corvette’s six-speed automatic requested equal time to upgrade their game.

Control integration systems manager Jim Springer explains, “Corvette owners have urged us to tighten up the response between a command at the steering wheel paddle and an up- or downshift. That’s an area we’re always striving to improve, so we used the 2008 model year to implement strategies we’ve developed.”

During downshifts, a new “quick shift” technique automatically raises engine rpm in the brief interval between the release of one gear and the engagement of the next. It took an intense calibration effort and cooperation from Corvette engine experts to refine how it works, but the end result is a 40-percent quicker response.

“Thanks to the scope and sophistication of our electronic controls, this improvement was accomplished in software with no hardware changes necessary,” says Springer.

“To quicken upshifts, we implemented a strategy called torque management,” he says. A momentary reduction in the amount of engine output shortens the torque phase of each paddle-commanded upshift.
The net result is a 25-percent faster response. Since minimal torque management is used when the transmission handles upshifts automatically, the sport mode should still be used if the driver’s priority is flat-out acceleration

“Three years ago, when I joined the Corvette group, I saw a major opportunity,” recalls Jim Mero, the vehicle dynamics engineer responsible for ride and handling development.

“The sixth-generation was born with good but not great steering. Working on other programs at GM, I had witnessed what could be accomplished when a capable supplier teams with development engineers to create a world-class steering system.”

The engine may be the heart of a sports car, but the driver senses a car’s soul through its steering. Porsches, BMWs, Ferraris and other bluebloods earned their renown by providing impeccable steering sensitivity.
Now that Corvette plays in the world-class league, every aspect of its performance — including steering feel — is measured by a platinum yardstick.

Mero used a “build it and they will come” tactic to get the steering upgrades he sought approved. “Talk gets you nowhere. Until you install improvements in a car that anyone can drive and experience for themselves, there are no believers,” he explains.

Corvettes are equipped with Magnasteer variable-effort rack-and-pinion steering manufactured by Delphi Steering Systems. The ‘magna’ part of the name refers to one of the two channels by which power assistance is tuned to achieve the desired dynamic characteristics.

A magnetic field surrounding the pinion shaft is adjusted by an electronic controller to alter effort as desired. The second channel is hydraulic.
As effort rises, the control valve attached to the pinion shaft closes to deliver hydraulic pressure supplied by an engine-driven pump to an assist cylinder integral with the steering rack.

Magnasteer’s electronic controller monitors car speed and lateral acceleration via sensors. Corvette engineers program the controller to reduce the amount of steering assistance as speed and cornering g’s rise.

This allows the car to feel responsive to the driver’s inputs without sacrificing stability and predictability. Mero adds, “Generally speaking, lower steering friction yields a clearer communication between the tires and the driver. Steering effort must rise in a linear progression to send a clear message to the driver that the car is working harder in a corner.”

Mero sought improvements in linearity, sensitivity and precision beyond what could be achieved by routine external calibrations.
To achieve these gains, he challenged Joel Birsching, a product engineer at Delphi, to dig deep inside the Corvette’s steering gear.

To hit the ambitious performance metrics GM engineers established, Birsching’s team changed every major internal component.
Friction throughout the system was analyzed and materials and processes were altered as necessary to meet GM’s requirements. The gear set was redesigned with new geometry to improve how precisely and smoothly the teeth mesh together.

Operating clearances were tightened. A new algorithm was created for the Magnasteer controller to provide higher on-center stiffness. (Engineers define stiffness as the amount of motion at the steering wheel rim before the car responds with a change in direction. Less motion equals higher stiffness.)

A concerted effort paid handsome dividends. Steering feel is notably improved in the 2008 Corvette. Chalk up one more category where America’s favorite sports car meets or exceeds the blueblood standard.

Last August, Gail Phillips of Pismo Beach, Calif., shattered the 183.904 mph record I set at Bonneville 29 years ago driving a 1979 Mazda RX7 in the E/GT class.
While my pride should be wounded, Phillips is such an avid Corvette enthusiast and speed demon, I can only congratulate her on the way my record fell.

Phillips graduated from driving top-flight vintage Corvettes to racing a 1999 coupe at Bonneville last year. She chose a Corvette because it has one of the lowest aerodynamic drag coefficients of any production automobile.

As such, it’s a natural to go to Bonneville with a minimum amount of changes.

So what does it take to make a Corvette go fast on the salt? Doug Odom, Phillips’ car builder and the owner of POP Motorsports, started with a theft-recovery Corvette and stripped it down. Then he added a roll cage, a height-adjustable suspension, a polycarbonate windshield and back window, and steel and aluminum cockpit plating.

To optimize aerodynamic performance, Odom lowered the Corvette’s ride height and installed side exhaust pipes configured to block air from flowing under the sides of the car.

Ducting helped reduce the amount of air entering at the front to the minimum needed for cooling and combustion. Odom also incorporated aero lessons learned during his NASCAR racing years; small longitudinal fences and a hinged panel were added to the roof to discourage flight in the event Phillips’ car got sideways.

These safety measures were never needed. During five passes down the salt, Phillips reported no hint of wheelspin or wobble.
Her No. 427 Corvette ran arrow-straight in spite of the low coefficient of friction between slick racing tires and the graded salt.
Odom’s data recorder revealed that both axles showed slight increases in down force at speed. All the aerodynamic development Corvette engineers invested in the original fifth-generation car paid off handsomely.

Phillips’ two-way average speed of 190.154 mph sent my record packing. By the time this issue goes to press, she will have attacked the 209-mph D/GT record in the same Corvette, but only after the 4.2-liter, 450-hp small block that earned her E/GT record is replaced by a 5.0-liter, 600-hp engine built by Odom.

I feel lucky in one respect: Gail Phillips won’t have broken my one remaining Bonneville record, set in a twin-turbo RX7 — at least not this year.

Considering the bullets Corvette engineers sweat over ounces of mass, the 22-pound weight gain necessary to upgrade the Z06’s LS7 engine to full dry-sump lubrication must have caused palpitations.

“The conventional wet-sump approach used successfully with the LS2 V8 could not meet the LS7 performance targets,” says design engineer Dan Hommes.

Dry-sump lubrication is de rigueur in racing, at least whenever the rules allow. Evacuating the oil from beneath the crankcase accomplishes two ends — a lower center of gravity with the engine positioned closer to the pavement and better overall dependability.
While dropping the Z06’s engine was not practical in this instance, the potential lubrication benefits alone were worth it.

Hommes explains,

“The Z06 easily achieves over 1g in cornering and braking performance. That’s equivalent to tilting the engine at a 45-degree angle.
In a traditional wet-sump design, the oil migrates all over the bottom of the engine. When it moves away from the pickup, there’s an excellent chance the pump will be temporarily starved.”

With a 7000-rpm redline and highly stressed internal components, oil-pressure fluctuations are intolerable.

The dry sump carries most of its eight-quart supply of Mobil 1 (two quarts more than the LS2 V8’s capacity) inside a six-inch-diameter, 24-inch-tall cylindrical reservoir, where it’s on call to lubricate vital engine parts.

The LS7’s gerotor-type (pronounced GEE-rotor) oil pump is a two-stage design driven by the forward portion of the crankshaft. (Wet-sump systems use a single-stage oil pump.) One stage, supplied by a hose connected to the reservoir, is responsible for pumping oil pressurized to 60 psi through the filter and cooler before it returns to the block to lubricate other components.

The second stage scavenges oil that drains back to the sump and delivers it through a second hose to the remote reservoir located just behind the Z06’s right front tire. In addition to the external hoses, oil is routed through passages cast integrally with the LS7’s aluminum sump.

The storage reservoir is one clever piece of engineering. It consists of two aluminum castings welded and bolted to a thin-wall extruded-aluminum tube.

Oil from the engine enters the bottom, squirts up through an internal tube, and spills down along the tube’s inside wall when it reaches the upper casting’s radial drain holes.

This circuitous route separates entrained vapors (bubbles) and dispenses heat.Windage caused by the spinning crankshaft never has a chance to stir air into the lubricant.

Thanks to the dry sump, Z06 owners are able to exercise their herd of horses, confident that every pony is well lubed.