In our April 2013 issue, we went one-on-one with the GM powertrain teams responsible for the new LT1 V-8, which is standard equipment in all ’14 Corvettes. We showed you the engine’s block, rotating assembly, and oil and cooling systems, and divulged these components’ inner secrets.
This month, the LT1's top end enters our spotlight. We've asked the engine’s Design Responsible Engineers to take us step-by-step through what makes the rest of the Gen V small-block so remarkable.
“The LT1 is the most significant redesign in the small-block’s nearly 60-year history,” says GM Assistant Chief Engineer/LT1 John Rydzewski. “It produces 231 percent more power from only 42 percent larger displacement, compared with its great-great-grandfather, the 195hp, 265ci Chevy small-block from ’55.
“We want our Corvette engines to not only exceed customer expectations, but also to be the best,” Rydzewski says. “To do this we count on innovation and years of experience that go into every part. Just as every picture can tell a story, we go to great lengths to make sure every part of the LT1 will tell a future story of durability and performance.”
So what specific innovations is Rydzewski referring to?
“Direct injection, Active Fuel Management, continuously variable valve timing, and a radically new advanced combustion chamber, which produces 11.5:1 compression yet retains 87-octane fuel compatibility—all brought together for the first time in the LT1 small-block,” he says. “Calling out the LT1's advanced combustion system, it’s so revolutionary that a Society of Automotive Engineers (SAE) paper is being written to explain GM’s combustion-system development process.”
Come along with us now as Rydzewski and his team examine the next-gen LT1's top-end, including its heads, valvetrain, combustion chambers, compact fuel system, and more. We’ll reveal details of the LT1's advanced technologies, and hear its Design Responsible Engineers reveal previously top-secret information about it.
Camshaft with Cam Phaser
Description: The LT1’s camshaft and cam-phasing systems were developed to work synergistically to provide sufficient variable-cam-timing authority and actuation performance, resulting in optimized power, torque, fuel efficiency, emissions, and smoothness. The LT1’s hydraulic roller cam is based on the highly successful LS3 cam’s tuning of 14mm gross intake lift, and variable valve timing of 62 crank degrees of cam-phasing authority.
The LT1 cam features 200-/207-degree duration, 0.551- /0.524-inch lift, and a 116.5-degree lobe-separation angle. Its PN is 12629512.
Like the Gen IV LS3, the Gen V LT1 cam starts with SAE 5150 billet steel, which is machined down (milled, drilled, and ground) into the shape of the cam.
This new cam’s other significant difference from its Gen IV sibling is its tri-lobe design, which drives the new fuel pump.
Design responsible engineer: Mark Stabinsky/LT1 Valvetrain
His insider’s perspective: “The Gen V LT1 differs from the Gen IV LS3 in that the lobes of the LT1 have their final profile ground in after they are hardened, whereas the LS3 is ground soft then hardened.”
Description: Cast from 319-T7 aluminum, raw LT1 heads proceed through flexible modules, where 11 CNC machines per module use 15 spindles and 44 unique cutting tools to machine their six planes.
Nitrided Silichrome-1 intake and sodium-filled exhaust valves measuring 2.13/1.59 inches (intake/exhaust) are installed in the head at 12.5 and 12 degrees, respectively. In contrast, the Gen IV engine featured 15-degree valves.
There’s also a change to the intake and exhaust ports in Gen V. They’re raised to allow packaging of the direct-injection (DI) system below them (the only place it would fit) and feature a twisted shape, which directs the air to enhance mixing of the charge.
The LT1 heads are designated PN 12620545, and will likely to become known as “545” heads by Corvette enthusiasts.
Design responsible engineer: Dennis Gerdeman/LT1 Cylinder Heads
His insider’s perspective: “Robots do some of the cylinder-head assembly, such as the valves and valve seats, but pushrods are still assembled by human hand.”
Description: The LT1’s valvetrain incorporates two lifters per cylinder. When both are engaged, the engine operates as a V-8; when the engine-control module (ECM) deactivates two of the lifters, the engine becomes a virtual V-4. The pushrods are formed of SAE 1010 steel tubing with ASTM 52100 steel balls, and measure 7.8-inches long (between the gauge lines on the end of the balls) with an 8.7-inch outer diameter. They activate SAE 8620 steel non-offset rockers with a 1.8:1 ratio, which compress beehive springs that are 2 mm taller than the Gen IV units. They’re rated at approximately 90 pounds closed and 302 pounds open.
Design responsible engineer: Mark Stabinsky/LT1 Valvetrain
His insider’s perspective: “The valvetrain is designed to operate to 6,600 rpm, which is the fuel cutoff for the 2014 Corvette.”
Description: Made from M12-175 steel, a total of 10 head bolts secure each LT1 cylinder head to the block, for a total of 20 per engine. Nineteen of the bolts are 133 mm long; one is 101 mm long, as it would otherwise interfere with the timing chain. A computer-controlled multiple-spindle system implements a multiple-step torque/angle-to-yield strategy to secure all 10 head bolts in one head simultaneously.
Design responsible engineer: Ken Steffen/LT1 Fasteners
His insider’s perspective: “The LT1’s head bolts are similar to those engineered for the LS9, giving this new V-8 more load capacity than its other Gen IV predecessors.”
Direct Injection Fuel System(including Pump and injectors)
Description: Direct injection had never been implemented on a GM small-block before, so computer analysis drove the design of not only the DI, but also of other engine components such as the intake manifold, oil pan, and more.
The LT1’s DI system uses an enginemounted, camshaft-driven, high-pressure fuel pump and two hidden fuel rails under the intake manifold, which suspend the 126-lb/hr fuel injectors under the intake ports. The “smart” fuel pump utilizes control logic to minimize mechanical impact.
Design responsible engineer: Dustin Gardner/LT1 Fuel Deliver
His insider’s perspective: “The LT1’s direct fuel-injection system can deliver over 150 lph of fuel at 2,175 psi directly into the combustion chambers. As a point of reference, the LS3 port injection system runs closer to 58 psi.”