The C7 Corvette Chassis, Pt 6: The Chassis Tadge Juechter Built

Tagdge Juechter’s Genesis Program C7 Chassis

 

Dateline: 1-20-20, Illustrations & graphics by K. Scott Teeters – The C6 Corvette was a much-improved C5 and was well-received upon release. Fans liked the crisp new look, the new interior (for a while), and the extra grunt. Since the successful arrival of the performance Z06 model in 2001, every new generation Corvette is expected to have a Z06. Within minutes of the C6’s debut, the next question was, “Where’s the Z06?” The following year when the C6 Z06 was unleashed, there was an unanticipated surprise; an aluminum chassis.

This wasn’t on anyone’s wish list and was a total surprise. It wasn’t even on Zora Arkus-Duntov’s Christmas list! Weighing in at just 3,132-pounds, you have to go back to 1964 to find a lighter Corvette (3,125-pounds). Powered by the mighty 427 LS7 engine with 505 net-horsepower, with C5-R suspension technology, the C6 Z06 was better suited for the track, although many learned how to drive the new beast successfully on the street. The C6 Z06’s aluminum chassis had no trouble handling 638-horsepower in the ZR1 configuration. Bravo Corvette chassis engineers!

When Tadge Juechter’s C7 Corvette debuted, fans were stunned to learn that the base model C7 was built an even better version of the Z06’s aluminum chassis. But wait, there’s more! The same new aluminum chassis would be used for the coupe AND convertible Corvette. This was a major breakthrough and bespeaks of advanced engineering. Here’s how Juechter’s team did it.


Juechter’s objective was to build a modern performance car that delivered enhanced driving experience, more efficiency that yielded more performance. Every element had to contribute to the overall performance and there would be nothing fake. That explains everything that we see on the C7 Corvette, but what’s unseen is even more amazing.

As we learned from the C5 with its hydroformed side rails, stiffness matters. Juechter is on record stating that while hydroforming was an engineering game-changer, the downside is that parts have a uniform thickness; even in areas where it isn’t needed. Hydroformed parts cannot be tailored for areas that need greater or less strength. Enter the Genesis Software Program.

This is almost computer magic. Engineers first determine the overall block space they want; length, width, and height. Then they determine where they want to place the major components; engine, transmission, suspension assemblies, cabin parts, etc. This creates negative spaces where the structure needs to be to hold everything together. The Genesis Program then synthesizes an optimum structure so that engineers can then take the load design and break it down into parts that can be fabricated and joined together. Afterward, dynamic stress and crash testing is performed and parts modified to meet predetermined objectives.

The C7’s hydroformed aluminum frame rails were optimized for the best the aluminum industry could offer, in terms of tensile strength, lightweight, and materials-joining technology. New aluminum metallurgy and aluminum fastening technologies allow engineers to augment the hydroformed frame with 7000-Series aluminum extrusions designed for specific areas; such as engine/front suspension assembly, transaxle/rear suspension assembly mounting points and frontal collision areas.

Careful consideration to the placement of major components was also critical. Juechter’s team felt that the C6 was slightly nose-heavy. Components were adjusted so that the C7 is now rear-biased, allowing more load on the rear wheels for better traction at launch; like a racecar. The front wheels were moved forward 1-inch making the wheelbase 106.7-inches. This is the longest wheelbase Corvette ever made. The shortest was the C4, measuring 96.2-inches. Moving the wheels forward also allowed for more space under the hood for the new LT1 engine and various auxiliary systems. This also preserved “crash space” in the front.

Offering an aluminum frame for the coupe and convertible was a big challenge for the team. But because the basic frame structure is so strong, it didn’t need additional roof structure via a fixed roof. The net result is that not only can the Z06 and ZR1 have lift-off rood panels, but both can also be offered as a convertible. This was unimaginable for the C5 Z06, C6 Z06, and the C6 ZR1. According to Ed Moss, the C7 structural engineer group manager, his engineering team tailored sixteen different thicknesses of various grades of aluminum from 11-mm to 2-mm. The completed C7 aluminum frame is 100-pounds lighter than the C6’s steel frame and is 60-percent stiffer. Juechter said that engineers consider the C7’s aluminum chassis to be the most beautiful part of the C7. Perhaps someday Chevrolet will offer a transparent carbon fiber body option.

The C7 frame was also designed for aerodynamic efficiency. In the past, engineers tended to only consider how air passed over and under a performance car. The C7 literally breathes. Spaces under the car’s skin and in between the chassis structure were designed for the internal ducting for engine cooling, brakes, transmission, and differential cooling, and venting. Other spaces allowed for electrical and plumbing fixtures for coolant, fuel, and air conditioning ducting.

The C7 design team worked closely with the Corvette Racing Team on airflow management because even racecars are concerned about fuel consumption, as well as top speed dynamics and stability. Two of the most obvious ducting and venting features is the air extractor on the hood, and the NACA ducts on the top of the rear fenders.

Image: GM Archives

Taking a lesson from the C6.R Corvette racecars, the C7’s radiator is tilted forward. One-third of the air that passes through the radiator is vented out of the hood. The hood louvers are angled so that the exiting air flows tightly over the car creating additional downforce to the nose of the car; thus eliminating the dreaded nose lift.

Heat exchangers (radiators) for the transmission were placed in the back, close to the transaxle with air ducted through the NACA duct feeding into the heat exchangers and then vented out through vents next to the taillights. This is just another example of how every element on the C7 has a defined purpose.

All of the foundational work that went into the C7’s chassis laid down a structure what was easily adaptable to the $2,780 Z51 suspension option that included; performance brakes with slotted rotors; dry-sump oil system; suspension upgrades; special wheels and tires; electronic limited-slip differential with a cooler, performance gearing, and an aero package. The Z51 was for drivers that wanted to use more of the C7 460-horsepower and explore the pleasures of the C7’s superior structure.

The 2015 Z06 with its supercharged 650-horsepower LT4 engine, wide-body, suspension, and tire enhancements work wonderfully with the C7’s basic structure. The same can be said for the 755-horsepower ZR1; the basic structure is up to the task. Arguably, the most interesting use of available C7 components is the Grand Sport. It has the aggressive-looking Z06 body and suspension parts that take using the base model’s 460-horsepower to a whole new level.

I will now go out on a limb. At the C7 ZR1 debut in 2018, Juechter said that his engineers had taken the C7 as far as they could with the ZR1. Are they working on a C9 Corvette to sell alongside the mid-engine C8? If so, will it be built on a carbon fiber chassis? When it comes to Corvettes, things always evolve upward. – Scott

Corvette Chassis History, Pt 1 – C1 Chassis – HERE

Corvette Chassis History, Pt 2 – C2/C3 Chassis – HERE

Corvette Chassis History, Pt 3 – C4 Chassis – HERE

Corvette Chassis History, Pt 4 – C5 Chassis – HERE

Corvette Chassis History, Pt 5 – C6 Chassis – HERE

 


 

Chassis History, Pt 5: Dave Hill Strikes Again! Delivers evolutionary, but superior C6

Dave Hill’s 2006 Z06 stunned everyone with its stiffer than stock aluminum frame.

Dateline: 1.17.20 – Graphics by K. Scott Teeters, Images from GM archives: Corvette fans have been frustrated for years with Chevrolet’s evolutionary Corvettes. The “pie-in-the-sky” mid-engine Corvette has been around since the 1960s and anything less was evolutionary. The pending C8 aside, the C5 was the most revolutionary Corvette; because of the hydroformed steel perimeter frame, center backbone, all-aluminum LS1 fuel-injected engine, and transaxle. The C5 was the most solid Corvette ever offered and allowed engineers to vastly improve the basic suspension, the Z51, and the Z06. The racing C5-R won its class at Daytona in 2001 and 2003; won its class at Sebring in 2002, 2003, and 2004, and won its class at Le Mans in 2001, 2002, and 2004. This never would have happened without the superior basic C5 chassis. Dave Hill’s team got the C5’s chassis design so right that by 1999 they determined that a C6 needed to be started.

Whereas the C5 structure was revolutionary, the C6 was evolutionary. While the C6 chassis is different from the C5, it is essentially the same hydroformed steel perimeter frame with a center backbone, with the engine, torque tube, and transaxle all as stress members of the overall structure.

Photo: GM Archives

Let’s start with the basic C6 chassis. The chassis has a 1.2-inch longer wheelbase of 105.7-inches, but the overall length is 5.1-inches shorter than the C5 chassis. To achieve this, engineers shortened the frame rails 2.4-inches and changed the tube-formed front bumper beam to a unit made with two channels welded together to save 2/3s of an inch. The shorter frame with less overhang on the body achieved a total of 5.1-inches of length on the C6, over that of the C5. The shorter frame also increased the torsional stiffness. And to reduce squeaks, rattles, and vibrations, high-strength steel braces were added to the frame to improve structural rigidity.

Weight savings were picked up by using extruded aluminum beams in the interior instead of the cast aluminum beams from the C5. The instrument panel has additional brackets for the beam under the dashboard. Side-impact beams were made of aluminum and saved 4.5-pounds, plus the doors do not have traditional latch and lock mechanisms. Aluminum braces were used through the structure to improve crash performance. The front skid-bar in front of the radiator is also aluminum. An aluminum panel that saved 1-pound and increased stiffness replaced the steel driveline panel under the driveline torque tube. To increase upper rigidity, the windshield frame has extra gussets. And the trunk uses lightweight plastic braces. Corvette systems engineer Ed Moss said, “We are making it (the C6) smaller, lighter, but stiffer.”

The issue of stiffness in high-powered sports cars with wide tires cannot be under-estimated. Increased grip, torque, and horsepower will put tremendous added stress to a performance car’s structure. Imagine what would happen if a LT5 engine and big tires were applied to a stock C1 chassis. The C5 1999-2000 Corvette Hardtop, with its bolted and bonded hardtop increased the overall structural stiffness by 12-percent, enough to make it an excellent base to build the Z06 upon. The basic C6 platform offered a significant improvement in stiffness that made it an excellent platform to build the Grand Sport that used Z06 suspension parts and wide tires. Without any increase in power, the Grand Sport was a better Corvette. Stiffness matters.

Photo: GM Archives

While the C6’s suspension is similar to the C5’s, there are no carryover parts. The basic design of the short-long A-arms, transverse composite leaf springs independent suspension is the same. The control arms, springs, dampers, bushing, sway bars, and steering gear are all completely redesigned. New hub knuckles and dampers allow for greater suspension travel thanks to improved clearance. One issue with C5s was road noise and twitchiness on rough roads. To improve handling and ride, steering geometry and the progressive rates of the composite springs were improved.

Like the C5 the C6 offered customers three levels of suspension performance. Chevrolet calls the basic C6 suspension, “tuned for balance, ride comfort, and precise handling.” This is for the customer that wants a Corvette because they like “driving a Vette” with 400-horsepower on tap when they want a brief thrill, but aren’t interested in exploring the limits of tire grip.

Photo: GM Archives

The F55 Magnetic Selective Ride Control was a $1,695 option with some amazing technology. Magnetorheological dampers use metal-infused fluid that controls the viscosity of the fluid with a magnetic field created by an electromagnet. This semi-active suspension adjusts the fluid via a computed to adjust damping rates based on road surfaces down to the millisecond. The active handling and antilock systems were smarter and less intrusive.

And for the enthusiast that doesn’t want to go for the serious big gun Z06, but wants the most from their base model Corvette, there was the $1,495 Z51 Performance Package. The F51 option has been around since 1984 with a starting price of $600 with prices fluctuating through to 1990. Then from 1991 to 1995 Chevrolet offered the $2,045 Z07 Adjustable Suspension Package. The Z51 option was back in 1996 but consisted only of stiffer springs and stabilizer bars for $350 from 1996 to 2003, then $395 in 2003 and 2004.

Photo: GM Archives

The Z51 was part of the C6 lineup from 2005 to 2009 and was a whole different animal. Costing $1,495 in 2005, then $1,695 from 2006 to 2009, the Z51 package was the most comprehensive Z51 package ever offered, consisting of; higher rate springs and shocks; larger sway bars; larger cross-drilled rotors – 13.5-inch diameter on the front and larger 13-inch diameter on the rear; coolers for the engine oil, transmission, and power steering; higher-grip Goodyear EMT tires; revised gear ratios for the 6-speed cars.

Photo: GM Archives

An interregnal part of the overall objective of a smaller, lighter, and stiffer C6 was the body. For the body part of the C6, designers wanted to improve the fit of the body panels and reduce weight. For the broad flat parts, such as the hood, doors, trunk lid and tonneau cover on the convertible, SMC – Sheet Molded Compound was used. This is a fiberglass mixed with resin that is compressed into a mold, with a chemical reaction and the heat from the compression curing the part. For more complex shapes, such as the front grille and the rear fascia, PRIM – Polyurethane-Material Reinforced-Reaction Injection Molding was used. The removable roof panel was made from Polycarbonate, either transparent or painted.

Photo: GM Archives

But the major breakthrough for the C6 chassis was the all-aluminum chassis for the Z06 and the ZR1. The basic chassis design is the same except that the hydroformed side rails are made of 4-mm 5745 aluminum alloy. The standard C6 steel frame thickness was 3-mm and weighs 502-pounds while the aluminum Z06 frame weighs 392-pounds; that’s 110-pounds lighter, or 22.5-percent lighter. The Z06 frame is 50-percent stronger in torsional and bending stiffness. The Metalso Metal Fabricator, in Hopkinsville, Kentucky manufactured the aluminum frames and then shipped them to the Corvette Bowling Green assembly plant. The engine cradle and fixed-roof panel are magnesium, and the floorboards were carbon fiber.

Everything tends to move upward in the world of Corvettes. When the Z06 debuted in 2006, no one imagined that the C7 base Corvette would ride on a C6 Z06-like chassis.

Scott

Corvette Chassis History, Pt 1 – C1 Chassis – HERE

Corvette Chassis History, Pt 2 – C2/C3 Chassis – HERE

Corvette Chassis History, Pt 3 – C4 Chassis – HERE

Corvette Chassis History, Pt 4 – C5 Chassis – HERE

Corvette Chassis History, Pt 6 – C7 Chassis – HERE