John Rydzewski, assistant chief engineer for GM’s small-block (OHV V8) engines, seems justified in his pride regarding the role his 755-hp LT5 V-8 played in achieving the scorching performance—a quarter-mile run in 10.6-seconds at 134 mph (216 km/h) and a 212-mph (341 km/h) top speed in the new 2019 Corvette ZR1.
Although those stats are impressive, here’s one that engine developers will find significant: a specific output of 2 hp per cubic inch, remarkable for a single-cam pushrod V8 with lineage reaching back to 1955.
Building from LT4 foundation
The 2019 LT5 builds on the fifth-generation small-block V8 architecture introduced in 2014 for the seventh-generation Corvette Stingray. The 6.2-liter deep-skirt aluminum block, aluminum cylinder heads, continuously variable cam timing, variable-displacement oil pump, piston cooling jets and dry-sump lubrication all carry over from the supercharged and intercooled LT4 variant introduced for the 2015 Corvette Z06. The new LT5 engines are hand-assembled at the Bowling Green, Kentucky, Performance Build Center located within the Corvette assembly plant.
To increase peak output by 105 horsepower and maximum torque by 65 lb·ft (88 N·m) versus the LT4, most of the components topping the LT5 engine are new:
- The Eaton-developed Twin Vortices Series (TVS) supercharger’s displacement is 52% larger to deliver substantially more intake air. This blower is spun 2.4 times crankshaft speed versus the LT4’s 3.1:1 drive ratio. Peak boost rises from 9.4 to 14 psi. A side benefit of the new supercharger design is that the LT5 is quieter than the Z06 in its Tour driving mode.
- The larger supercharger consumes just 1 hp during cruising—but a significant 110 hp while delivering maximum airflow and boost. The LT4’s peak parasitic loss is 94 hp.
- The LT5’s forged-steel crankshaft has a larger key slot at its forward end to handle the new supercharger’s drive load. A new alloy steel for the crank provides higher tensile and yield strength. Main bearing inserts have been upgraded to a tri-metal material. Both the 8-speed automatic transmission’s flex plate and the 7-speed manual’s flywheel are fortified for LT5 service. The number of ribs in the drive belt is increased from eight to 11.
- The LT5’s 95-mm (3.74-in.) throttle body is 8 mm (0.31-in.) larger than the LT4’s inlet plate and a new blower bypass valve vents excess air more efficiently. If the stock 755 hp isn’t quite sufficient, a $625 dealer-installed performance air intake system (engineered to fit all current Corvettes) adds 17 hp.
- Two significantly larger intercoolers double the LT4’s charge-air heat rejection, necessitating a 73 mm (2.9-in.) increase in the height of the intake plenum cover. The plenum and its decorative carbon-fiber cover both project through the ZR1-specific ‘halo’ hood.
- To supplement the direct fuel injection during high-load conditions, a new port-injection system operated by a second electronic control module has been added to the LT5.
Fire from the pipes
The Active Fuel Management (cylinder deactivation) strategy employed to maximize the LT4’s fuel economy is not fitted to the LT5 engine. Corvette ZR1 customers thus face a $2100 gas-guzzler tax. During high-speed testing on the German autobahn, engineers consumed an 18.5-gal (70-L) tank of fuel in 15 minutes of flat-out running.
When two muffler valves—one passive and one electronically controlled—open in the more aggressive driving modes, an 800° stream of exhaust trails the ZR1 with visible flames in low-light conditions.
The all-new factory-fill lubricant is Mobil 1 ESP (Emission-System Protection) Dexos 2, SAE grade 0W40 synthetic.
The 2019 ZR1’s 212-mph top speed was achieved in seventh gear in a car equipped with the 8-speed automatic transmission and the standard low-mount rear wing. The convertible drops top speed to 208 mph (335 km/h), while the optional high-mounted wing and front splitter package trim terminal velocity by 10 mph (16 km/h). A 215-mph limiter is included to protect the Michelin tires when conditions might allow exceeding that speed.Continue reading »