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.”
Description: The LT1’s combustion chambers are optimized to take advantage of direct injection, continuously variable valve timing, and Active Fuel Management (AFM). Its overhead-valve, two-valves-per-cylinder arrangement is completely different than the Dual Overhead Cam (DOHC) design of GM’s other direct-injected engines. The flow field—that is, the motion of the air/fuel mixture—is more complex in the LT1 than in GM’s DOHC engines, and the LT1’s direct injection requires more mixture swirling for optimal combustion.
The LT1’s spark plugs are moved closer to the center of the combustion chambers, specifically to push the flame closer to the center of the cylinder for increased efficiency and reduced knock.
Its new combustion chambers have a higher compression ratio than the LS3 (11.5:1 versus 10.7:1), and better knock tolerance than previous Chevy V-8s.
Design responsible engineer: Brian Pryor/Small Block Lead Analysis Engineer
His insider’s perspective: “The combustion-system performance in these cylinder heads is outstanding. We improved performance by switching the exhaust- and intake-valve positions within the combustion chamber, and optimizing port airflow. Corvette customers will immediately appreciate the engine performance improvement resulting from the enormous amount of work that went into developing this system.”
Description: Thanks to a clean-sheet design, the Gen V LT1 manifold shares no carryover content with the Gen IV LS3. This new manifold features a thermally efficient, four-piece, molded-and-welded composite design; “runners in a box” architecture; a PCV foul-air tube; and an integral manifold cover with copolymer-filled acoustic barrier.
It weighs 9.92 pounds by itself, or 12.45 pounds with its manifold cover and noise insulator installed.
GM engineers were able to improve manifold dynamic airflow 3.6 percent and reduce airflow imbalance 50 percent, compared with the LS3.
Design responsible engineer: Tim Carr/LT1 Intake Manifold
His insider’s perspective: “We learned from the Gen IV intake that when a runner shares a plenum wall, air is blocked from entering the runner by that surface. That drove the implementation of the ‘runners in a box’ design, which means the manifold runners are suspended in the manifold plenum, giving more of the runner entry for air to enter. The result is reduced airflow restriction and improved engine performance.”
Description: The LT1’s 87mm electronic, single-blade throttle body employs a non-contacting throttle position sensor (TPS) and a digital communication protocol to interface with the enginemanagement system. In contrast, the Gen IV throttle body’s TPS used a contacting sensor with an analog output signal. The driveby- wire system from Gen IV continues forward to Gen V, although it was reengineered specifically for this new engine.
Design responsible engineer: Ted Kuzmanov/LT1 Throttle
His insider’s perspective: “In conjunction with a more powerful DC motor and enhanced gear set, the new TPS arrangement allows the throttle body to achieve faster and more accurate throttle control.”
Active Fuel Management System and Lifter Oil Manifold Assembly
Description: Active Fuel Management is not new to GM. The company introduced it in 2004, and approximately 4.6 million GM vehicles are currently equipped with this technology. The LT1’s Active Fuel Management (AFM) system uses ECM-controlled deactivation lifters to shut off cylinders 1, 7, 6, and 4, creating a virtual V-4 with an 8-2-5-3 firing order. The system saves fuel during light throttle, yet enables maximum engine performance when the driver demands it. Under cylinder deactivation, the Lifter Oil Manifold Assembly (LOMA) routes oil to the necessary lifters via four lifter-oil solenoids. The AFM sensors are lightning quick, capable of returning the LT1 to eight-cylinder performance in three-tenths of a second.
Design responsible engineer: Mark Stabinsky/LT1 Valvetrain
His insider’s perspective: “Active Fuel Management validation consisted of cycling the LT1 engine in and out of the cylinder-deactivating feature 100,000-plus times at a variety of engine speeds to ensure the performance and durability of its unique valve lifters.”
Rocker Covers and Ignition System
Description: One of the most distinctive features of the Gen V LT1 is its domed rocker covers. They house a patent-pending integrated positive crankcase ventilation (PCV) system, which enhances oil economy and life, reduces oil consumption, and contributes to low emissions.
The covers serve another critical purpose in LT1 architecture: They hold the direct-mount ignition coils for the coilnear- plug ignition system.
Between the individual coil packs, the domed sections of the covers contain baffles that separate oil and air from the crankcase gases—effectively about three times the oil/air separation capability of Gen IV small-blocks. Each cover features an inlet and outlet path for the crankcase gases, with the separated oil dropping back onto the engine within the covers, and the remaining air/gases circulated back into the air-intake stream for combustion. They also serve to draw filtered fresh air into the crankcase to remove combustion byproducts, preventing sludge and increasing oil life.
Design responsible engineer: Alan E. Rice/LT1 Lubrication and Ventilation
His insider’s perspective: “We were challenged to develop a system that functions for the typical driver and meets the performance requirements of the advanced driver. After many hours in the lab and on the track optimizing the ventilation system of the Gen V LT1, we have achieved that goal.”
Description: The LT1’s four-into-one short-header exhaust manifolds are a cast variant of the tube-and-jacket design used on the Gen IV LS7 and LS9. The new manifold’s near-equal-length runners ensure all cylinders have consistent flow of exhaust gases. These new headers also reduce radiated noise in the engine compartment, compared with the LS7 and LS9.
Design responsible engineer: Ken Marotta/LT1 Exhaust Manifolds
His insider’s perspective: “GM engineers further optimized the manifolds’ runner geometry to develop cross sections, which minimize restriction and maximize volumetric efficiency of tuning of the exhaustgas flow.”