Compared to the LS3 cylinder head design, the LT1 head features a smaller 59cc combustion chamber, which is designed to complement the volume of the piston dish. The smaller chamber size and dished pistons work together to produce an 11.5:1 compression ratio vs. the LS3’s 10.7:1 compression ratio. The spark plug angle and depth have been modified with the LT1 head, too, to protrude farther into the chamber, placing the electrode closer to the center of the combustion to support the direct injection system. In addition to the new combustion chamber design, the Gen V head features large, straight and rectangular intake ports that feature a slight twist to enhance mixture motion. This is complemented by a reversal of the intake and exhaust valve positions as compared to the Gen III/IV design. The exhaust port shapes are optimized for the new valve locations, with new port opening locations at the manifold face. VALVES AND VALVETRAIN Large, lightweight intake and exhaust valves are used in the LT1 heads, with 2.13-inch hollow intake and 1.59-inch hollow sodium exhaust valves. The lightweight valves enable the engine to rev quickly and capably to greater than 6,000 rpm. LS3 valves measure 2.165 inches intake and 1.59 inches exhaust. The LT1’s valves are held at new 12.5 degrees intake/12 degrees exhaust angles vs. the LS3’s 15-degree angle. Additionally, the valves are splayed at 2.61 degrees intake/2.38 degrees exhaust to reduce shrouding and enable greater airflow. Roller-pivot rocker arms are used in the LT1 and feature a 1.8 ratio vs. the 1.7 ratio of LS3 rockers. The LT1’s reversed valve location also eliminates the offset design of the LS3’s intake-side rocker arms. Also: the LT1 uses 8.7mm (outside diameter) pushrods, which provide greater stiffness than the LS3’s 7.9mm design. That enables improved high-speed valvetrain performance. DIRECT INJECTION FUEL SYSTEM Direct injection is featured on all Gen V engines. The technology moves the point where fuel feeds into an engine closer to the point where it ignites, enabling greater combustion efficiency. It fosters a more complete burn of the fuel in the air-fuel mixture, and it operates at a lower temperature than conventional port injection. That allows the mixture to be leaner (less fuel and more air), so less fuel is required to produce the equivalent horsepower of a conventional port injection fuel system. This represents one of the fundamental differences between the engines. The LT1 features direct injection, with injectors positioned in the cylinder heads, while the LS3 features a conventional port injection system, with injectors located in the intake manifold. That difference alone makes it impossible to simply swap heads and intakes between the LT and LS families. The pistons play an integral role in the direct injection system, as they feature dished heads designed to direct the fuel spray for a more complete combustion. Design of this advanced combustion system was optimized after thousands of hours of computational analysis, representing one of the most comprehensively engineered combustion systems ever developed by General Motors. The direct injection system features very high fuel pressure, up to 2,175 psi (15 MPa) on most engines and as high as 2,900 psi (20 MPa) on the supercharged LT4 and LT5 variant, requiring a high-pressure, engine-driven fuel pump in addition to a conventional fuel-tank- mounted pump. On all Gen V engines, the pump is mounted in the “valley” between cylinder heads—beneath the intake manifold. It is driven by the camshaft at the rear of the engine. LT1-SPECIFIC FEATURES In addition to the features that compare and contrast with the LS3, the new LT1 has a number of unique components that simply aren’t shared with previous LS engines, including: • PCV-integrated rocker covers designed to reduce oil consumption • Cylinder deactivation that shuts down four cylinders in certain light-load driving conditions—and featuring unique, “collapsible” valve lifters for the deactivating cylinders • Four-into-one short-header-type exhaust manifolds similar to the LS7 design, but made of cast iron • Single-bore 87mm throttle body • Revamped cooling system with a new offset water pump design • The use of electric power steering on production models means there’s no provision for a conventional power steering pump on the accessory drive system. In summary, the lineage between the LS3 and the LT1 is clear, but where the LS3 was an evolution of previous LS engines, the LT1 is more of a new species. Therefore, mixing and matching parts between the LT and LS families isn’t practical or, in most cases, feasible. LV3 4.3L The 4.3L V-6 is the smallest Gen V engine and is based on the V-8 versions, but with two fewer cylinders—a design lineage that dates back to the previous 4.3L V-6, which was itself a Gen II Small-Block with a pair of cylinders removed. The bore and stroke dimensions are 3.92-inch (99.6 mm) bore x 3.62-inch (92 mm) stroke, for a displacement of 262 cubic inches. It is used in the Chevrolet Silverado 1500 and GMC Sierra 1500, where it is rated at 285 horsepower and 305 lb.-ft. of torque. L83 5.3L The L83 is the workhorse of GM’s full-size trucks and SUVs, including the Chevrolet Silverado 1500, Tahoe and Suburban, as well as the GMC Sierra 1500 and Yukon lineups. It has a smaller bore—3.78 inches (96 mm)—than other Gen V engines, but the same 3.62-inch (92 mm) stroke shared by all of them. It is rated at 355 hp and 383 lb.-ft. of torque. L86 6.2L The L86 6.2L is the largest, most powerful Gen V engine offered in GM’s trucks and SUVs, delivering 420 hp and 460 lb.-ft. of torque. A forged steel crank is unique among the truck engines, along with its larger 4.06 (103.25 mm) bore diameter. This engine is available in the Silverado 1500 and Sierra 1500 and is standard in the GMC Yukon and Cadillac Escalade. LT1 6.2L It’s the standard engine in the C7 Corvette Stingray and Camaro SS, where it is rated at up to 460 horsepower and 465 lb.-ft. of torque (with the optional exhaust system). It shares the same basic configuration and 4.065 x 3.622 bore/stroke dimensions as the L86, but features other unique components to generate its higher output. LT4 6.2L SUPERCHARGED The supercharged LT4 engine is the power behind the C7 Corvette Z06, the Camaro ZL1 and the Cadillac CTS-V, delivering a stunning 650 hp and 650 lb.-ft. of torque. Each component of the rotating assembly, from the crankshaft to the piston rings, is unique to the LT4 and necessary to support the boosted engine’s cylinder pressure. The LT4 produces 9.4 psi of intake boost with a 1.7L supercharger. LT5 6.2L SUPERCHARGED The supercharged 6.2L LT5 is the power behind the 2019 Corvette ZR1. The LT5 crate engine delivers 755 horsepower and 715 lb.-ft. of torque. An all- new, 2.65L supercharger (64 percent larger than the LT4’s supercharger) pumps out more boost and blows into a robust charge-cooling system with about twice the capacity of the LT4’s system. The LT5 also features the largest throttle body (95mm) ever on an LS or LT engine, an electronically controlled bypass for the supercharger, specific heavy-duty main bearings and more. The LT5 produces 14 psi of boost and is 2.5 inches taller then the LT4. 59 CHEVROLETPERFORMANCE.COM LS-SERIES CRATE ENGINES Gen V Small-Block Engines RPO Code Displacement (cu/in/Liters) Compression Ratio Horsepower Torque (lb.-ft.) LV3 262 / 4.3 11.0:1 285 @ 5,300 rpm 305 @ 3,900 rpm L83 325 / 5.3 11.0:1 355 @ 5,600 rpm 383 @ 4,100 rpm L86 376 / 6.2 11.5:1 420 @ 5,600 rpm 460 @ 4,100 rpm LT1 376 / 6.2 11.5:1 460 @ 6,000 rpm 465 @ 4,600 rpm LT4 376 / 6.2 10.0:1 650 @ 6,400 rpm 650 @ 3,600 rpm LT5 376 / 6.2 10.0:1 755 @ 6,400 rpm 715 @ 3,600 rpm L8T 400/6.6 10.8:1 401 @ 5200 rpm 464 @ 4000 rpm
