The new supercharged 6.2-liter LT4 engine that will power the 2015 Corvette Z06 will be rated at 650 horsepower with 650 lb-ft peak torque, making it the most powerful production car ever produced by General Motors.
Official SAE numbers were released today following months of speculation when Z06 was introduced at the Detroit Auto Show in January with only estimates of 625-plus horsepower. The LT4’s 650 horsepower rating (485kW) comes in at 6,400 rpm while the 650 lb-ft (881 Nm) pulls at a healthy 3,600 rpm.
“The LT4 small-block sets a new benchmark for power and torque at GM,” says Steve Kiefer, VP of GM Powertrain Engineering. “The engine also puts the new Corvette Z06 on par with the most powerful supercars offered in America.”
According to GM, the LT4 offers 457 lb-ft of torque just off idle and twists the crank at 625 lb-ft as quick as 2,800 rpm. It also maintains 90 percent of its peak torque from 2,500 to 5,400 rpm. For comparison, a Ferrari V12 produces 28 percent less peak torque at a much higher 6,000 rpm , even though it offers more total horsepower. The LT4 also crushes a Porsche Turbo S engine’s peak levels by 90 horsepower and 134 lb-ft of peak torque.
“Torque is the pulling power of an engine and the LT4’s abundance of it at every rpm in the engine’s speed range helps the Z06 accelerate quicker and respond nearly instantaneously,” adds Jordan Lee, chief engineer for small-block engines. “It’s the very definition of power on demand.”
Lee told EngineLabs in January that the early estimates would likely be surpassed but that conservative numbers were used for the vehicle introduction. Nearly every part of the new 5th-generation LT1 engine had to be modified to support the power and torque that the Eaton 1.7-liter twin-screw supercharger would add. Engine Labs has extensively covered the LT1’s introduction and offered an in-depth analysis of the enhanced combustion design.
For additional comparison, the LT4 outpowers the previous-generation 7.0-liter LS7 engine by 180 lb-ft of torque, and offers 46 more lb-ft of peak torque than the supercharged LS9 engine. at just 3,200 rpm, the LT4 pumps out an amazing 208 lb-ft more torque than the LS7. Of course, the LT4 easily surpasses the LS7’s 505-horsepower rating.
“The new LT4 engine builds on the design strengths of our previous supercharged engine and leverages the technologies introduced on the Corvette Stingray – direct injection, cylinder deactivation and continuously variable valve timing,” says Lee. “Our new, very compact supercharger also helps the engine make power more quickly, and perhaps more importantly, it helps produce more torque earlier in the rpm band.”
Some noteworthy features of the LT4 include Rotocast A356 T6 aluminum heads, titanium intake valves, forged powder-metal connecting rods, forged alloy pistons, stainless steel exhaust manifolds, aluminum balancer and dry-sump oiling. The LT4’s compression ratio is 10:1, which is rather high for a boosted engine. The new supercharger, while smaller than the LS9 model, spins much faster at up to 20,000 rpm. The smaller rotors spin up quicker to help with the low-rpm torque output.
The LT4 will be assembled at the new Performance Build Center at GM’s Bowling Green assembly plant and at GM’s Tonawanda engine plant in New York.