teamzr1
Supporting vendor
Shifting 500 lb (227 kg) of engine mass rearward by 7.5 feet (2.3 m) and moving 300 lb (136 kg) of transmission components aft by almost three feet transformed the 2020 Chevrolet Corvette Stingray into a budding supercar.
General Motors’ motive behind adopting a mid-engine layout for the eighth-generation (C8) Corvette was to improve acceleration, braking and handling via substantially increased rear-tire loading.
While numerous test-drive reviews and ‘Of the Year’ trophies mark that mission accomplished, there are lessons behind the hoopla: how GM engineers solved problems they encountered reinventing America’s sports car.
“Porsche was our primary benchmark, especially in reference to their PDK dual-clutch automatic transmission’s overall dynamics,” revealed executive chief engineer Tadge Juechter, in an interview with SAE’s Automotive Engineering.
He said GM also purchased a Ferrari 458 for testing and tear-down analysis.
The first running Stingray prototypes exhibited a high-frequency whirring noise emanating from accessory drives for the alternator, AC compressor and water pump located at the front of the engine.
This caused concern, as the noise was being generated only a foot from the occupants’ ears.
Insulation placed on the firewall wasn’t as effective in muffling the noise as the engineers had hoped, Juechter noted.
So, they analyzed Ferrari’s solution: an unusually thick rear window.
“For C8, we increased the thickness of that piece of acoustic glass to 8.6 mm (0.34 in), which is nearly three times as thick as the 3.2-mm (0.13-in) tempered glass shrouding the engine bay,” he explained.
Jordan Lee, global chief engineer for GM’s small-block V8, added: “It’s a balancing act – hearing the satisfying sounds, such as the engine’s throaty intake and exhaust rumble, over distractions such as belt whir, injector tick and valvetrain clicks.” He noted that while most competitors hard-mount their fuel injectors between the engine’s cylinder heads and fuel rails, GM has been using an isolated arrangement in the small block since 2014.
“For C8, GM’s NVH engineers invested extra effort in developing effective insulation materials and assuring that the seal around the laminated acoustic glass at the rear of the cockpit is sufficiently robust to hush the belt whir,” Lee said. Further dialing-in of build processes is aimed at eliminating audible fuel-injector noise in the production cars.
A related issue is that the driver’s view rearward is through both the near-vertical glass panel in the rear cabin bulkhead and the long, nearly horizontal hatch over the engine compartment. In addition to providing rear visibility, the bottom edge of the glass hatch and surrounding surfaces must vent heat and moisture from the engine bay.
What Juechter calls C8’s “chimney” passes large volumes of hot, wet vapor during rainy driving and when the car is parked following a drive. A fan helps vent that heat from the engine bay. In addition, all the electrical connectors subjected to road splash have weathertight seals.
When the hatch glass is soiled, the driver’s view to the rear is diminished. To address this concern, Corvettes with up-level 2LT and 3LT interior trim are equipped with a two-way center mirror. Mode one is a conventional view through the two glass panels. The second choice is an electronic display provided by a high-definition camera mounted to the trailing edge of the roof.
Assuming the lens is clean, the camera provides a broad rear view, unobstructed by the wide roof pillars and soiled hatch glass. As is not uncommon in other rearview camera-mirror applications, reviewers have reported that it takes a second or so for their eyes to focus when the camera view is in use. All Corvettes have a conventional backup camera as standard equipment.
Stymied by the FEAD
Given the C8’s aggressive cornering capability, powertrain engineers knew that it was essential to improve the 6.2-L LT2 V8’s lubrication system. Jordan explained that with the previous-generation Corvette, “dialing in the lube system was like threading a needle. We lost several C7 engines when the oil pickup in the tank was starved during high-g maneuvers.” Another issue was oil blown out the optional dry sump’s vent system.
To solve these problems, the C8 program opted for two additional scavenge pumps to assure that track performance would be uncompromised. “Thanks to the new engine-mounted dry-sump oil reservoir that’s now standard equipment, we encountered virtually no [oil-starvation] drama during development,” Lee reported. “We were astounded how well it works and throughout C8’s comprehensive test program we experienced only one engine failure.”
One challenge that has thus far stymied engineers is a straightforward procedure for replacing the front-of-engine accessory drive (FEAD) belts. Doing so requires dropping the entire engine-transaxle assembly from the car.
Corvette owners can only hope that will be a rare occurrence, necessary only every 100,000 miles or so.
While shuffling powertrain component locations, C8 engineers also switched from semi-elliptic composite suspension springs (pioneered on Corvette’ rear axle in 1981) to steel coils. “We would have preferred to keep the composite springs because they are quite efficient from a mass standpoint,” Juechter explained.
“Unfortunately, with our low-mounted engine and transaxle, there’s no room for the tall cross-car path that a rear composite spring requires. In a rearview of the chassis, the arc of the spring would occupy the exact same space as spinning transmission gears.”
Once C8’s rear suspension design changed to coil springs, the engineers had to follow suit in front. Juechter said this was because of the significant difference between composite- and coil-spring force-versus-deflection characteristics. “To match the ride and roll rates at both ends of the car—something we deem absolutely essential—we switched to a steel coil spring at each corner,” he explained.
General Motors’ motive behind adopting a mid-engine layout for the eighth-generation (C8) Corvette was to improve acceleration, braking and handling via substantially increased rear-tire loading.
While numerous test-drive reviews and ‘Of the Year’ trophies mark that mission accomplished, there are lessons behind the hoopla: how GM engineers solved problems they encountered reinventing America’s sports car.
“Porsche was our primary benchmark, especially in reference to their PDK dual-clutch automatic transmission’s overall dynamics,” revealed executive chief engineer Tadge Juechter, in an interview with SAE’s Automotive Engineering.
He said GM also purchased a Ferrari 458 for testing and tear-down analysis.
The first running Stingray prototypes exhibited a high-frequency whirring noise emanating from accessory drives for the alternator, AC compressor and water pump located at the front of the engine.
This caused concern, as the noise was being generated only a foot from the occupants’ ears.
Insulation placed on the firewall wasn’t as effective in muffling the noise as the engineers had hoped, Juechter noted.
So, they analyzed Ferrari’s solution: an unusually thick rear window.
“For C8, we increased the thickness of that piece of acoustic glass to 8.6 mm (0.34 in), which is nearly three times as thick as the 3.2-mm (0.13-in) tempered glass shrouding the engine bay,” he explained.
Jordan Lee, global chief engineer for GM’s small-block V8, added: “It’s a balancing act – hearing the satisfying sounds, such as the engine’s throaty intake and exhaust rumble, over distractions such as belt whir, injector tick and valvetrain clicks.” He noted that while most competitors hard-mount their fuel injectors between the engine’s cylinder heads and fuel rails, GM has been using an isolated arrangement in the small block since 2014.
“For C8, GM’s NVH engineers invested extra effort in developing effective insulation materials and assuring that the seal around the laminated acoustic glass at the rear of the cockpit is sufficiently robust to hush the belt whir,” Lee said. Further dialing-in of build processes is aimed at eliminating audible fuel-injector noise in the production cars.
A related issue is that the driver’s view rearward is through both the near-vertical glass panel in the rear cabin bulkhead and the long, nearly horizontal hatch over the engine compartment. In addition to providing rear visibility, the bottom edge of the glass hatch and surrounding surfaces must vent heat and moisture from the engine bay.
What Juechter calls C8’s “chimney” passes large volumes of hot, wet vapor during rainy driving and when the car is parked following a drive. A fan helps vent that heat from the engine bay. In addition, all the electrical connectors subjected to road splash have weathertight seals.
When the hatch glass is soiled, the driver’s view to the rear is diminished. To address this concern, Corvettes with up-level 2LT and 3LT interior trim are equipped with a two-way center mirror. Mode one is a conventional view through the two glass panels. The second choice is an electronic display provided by a high-definition camera mounted to the trailing edge of the roof.
Assuming the lens is clean, the camera provides a broad rear view, unobstructed by the wide roof pillars and soiled hatch glass. As is not uncommon in other rearview camera-mirror applications, reviewers have reported that it takes a second or so for their eyes to focus when the camera view is in use. All Corvettes have a conventional backup camera as standard equipment.
Stymied by the FEAD
Given the C8’s aggressive cornering capability, powertrain engineers knew that it was essential to improve the 6.2-L LT2 V8’s lubrication system. Jordan explained that with the previous-generation Corvette, “dialing in the lube system was like threading a needle. We lost several C7 engines when the oil pickup in the tank was starved during high-g maneuvers.” Another issue was oil blown out the optional dry sump’s vent system.
To solve these problems, the C8 program opted for two additional scavenge pumps to assure that track performance would be uncompromised. “Thanks to the new engine-mounted dry-sump oil reservoir that’s now standard equipment, we encountered virtually no [oil-starvation] drama during development,” Lee reported. “We were astounded how well it works and throughout C8’s comprehensive test program we experienced only one engine failure.”
One challenge that has thus far stymied engineers is a straightforward procedure for replacing the front-of-engine accessory drive (FEAD) belts. Doing so requires dropping the entire engine-transaxle assembly from the car.
Corvette owners can only hope that will be a rare occurrence, necessary only every 100,000 miles or so.
While shuffling powertrain component locations, C8 engineers also switched from semi-elliptic composite suspension springs (pioneered on Corvette’ rear axle in 1981) to steel coils. “We would have preferred to keep the composite springs because they are quite efficient from a mass standpoint,” Juechter explained.
“Unfortunately, with our low-mounted engine and transaxle, there’s no room for the tall cross-car path that a rear composite spring requires. In a rearview of the chassis, the arc of the spring would occupy the exact same space as spinning transmission gears.”
Once C8’s rear suspension design changed to coil springs, the engineers had to follow suit in front. Juechter said this was because of the significant difference between composite- and coil-spring force-versus-deflection characteristics. “To match the ride and roll rates at both ends of the car—something we deem absolutely essential—we switched to a steel coil spring at each corner,” he explained.
