Getting to Know the LT1 - Part 2

Part 2: We take a good look inside the C7's all-new engine, with help from the people who know it best

Christopher R. Phillip Sep 4, 2013 0 Comment(s)
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Combustion Chambers

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.

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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.”

Intake Manifold

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.

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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.”

Throttle Body

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.

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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.”

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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.

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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.”

Exhaust Manifolds

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.

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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.”


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