The LS/LT engine family tree continued sPECIAL NOTE ABOUT CRANKsHAFT BOLT PATTERNs Almost all LS-engine crankshafts use a 6-bolt flywheel/flexplate bolt pattern, but the LS9 uses a 9-bolt pattern and the LSA, LT1, LT4, L8T, L8P and LSX454 engines use an 8-bolt pattern. CONNECTING RODs LS connecting rods are very similar and interchangeable. Most are made of forged powdered metal, while the LS7 and LS9 rods are forged titanium. The LS9 rods feature a unique forging designed for the pressure and power level of forced induction. Rod lengths are similar, too, at 6.098 inches for 5.3L, 5.7L, 6.0L and 6.2L (including LSA) engines. The 4.8L engine uses 6.275-inch rods and the LS7 uses 6.067-inch rods. The LS9 uses 5.990-inch rods. Since 2006, LS rods use bushed small ends. PIsTONs The LS9 is the only production LS engine with forged aluminum pistons; all the others use hypereutectic (cast) aluminum alloy pistons, varied mostly by diameter to accommodate various bore sizes. LS cast pistons shouldn’t be used on applications greater than approximately 550 horsepower. Also, the LS7 piston’s inner bracing requires the use of the matching LS7 connecting rod. GEN V sMALL-BLOCK: ENTER THE “LT” ENGINEs Introduced on the seventh-generation C7 Corvette Stingray and GM’s full-size trucks and SUVs for 2014, the Gen V Small-Block ushered in the next era of the historic engine family. The Gen V engine family delivers greater efficiency, performance and durability thanks to a combination of advanced technologies— including direct injection, Active Fuel Management (cylinder deactivation) and camshaft phasing (variable valve timing)—that support an advanced combustion system. In 2020 the 6.6L V8 L8T was introduced for use in the Heavy-Duty pickup trucks. It is part of GM’s fifth-generation Small Block engine family and made its debut in the all-new 2020 Chevrolet Silverado HD and 2020 GMC Sierra HD. The L8T is built on a cast-iron Small Block, enabling it to have long-term durability. Aluminum heads and direct injection enable the engine to deliver more precise fuel control resulting in a higher compression ratio if 10.8:1. The L8T features a forged steel crankshaft, forged powder-metal connecting rods and additional high-strength components to provide the added strength and durability demanded by Heavy Duty customers. The L8T replaced the 6.0L V8 L96 engine and makes over 11 percent more horsepower and over 21 percent more torque. In 2024 GM Performance Engineering took the L8T to another level and launched the L8P. The L8P shares many of the defining characteristics of the L8T, including total displacement 6.6L. The L8P powerplant features a unique non-AFM camshaft based off the 6.2L V8 LT2 found in the Corvette Stingray. To accommodate the special camshaft, more performance-oriented intake/exhaust valves and springs were added and the piston material was upgraded. By combining the heavy-duty durability of the Silverado HD and Sierra HD trucks with the all-out performance of the C8 Stingray, Chevrolet Performance has created a powerplant that is capable of satisfying many horsepower-hungry enthusiasts. Structurally, the Gen V small-block is similar to the Gen III/IV engines, including a deep-skirt cylinder block. Refinements and new or revised components are used throughout, including a revised cooling system and all-new cylinder heads. The engine is also designed to accommodate an engine-driven high-pressure fuel pump for the direct-injection system. As builders adapt the LT1, L8T, L8P or the supercharged LT4 or LT5 variant to their project cars, it’s logical to ask about the differences between the LS family and the new LT engines and whether parts interchangeability is as easy—or even possible—as it was between the Gen III and Gen IV engines. The short answer is no. Despite significant similarities in the basic architecture, there are a number of key differences between the new LT family and the LS family that prohibit simple interchangeability. Here’s a look at how the LT and LS families differ in those key areas, comparing the LT1 to the LS3. Most of the LT1 features match the features on the supercharged LT4 and the LT5. Note: L8T and L8P have a cast-iron block. NOTE: While structurally similar, almost none of the parts and components from the Gen V are interchangeable with Gen III and Gen IV engines. CYLINDER BLOCK AND OILING sYsTEM Like every Small-Block generation before it, the Gen V cylinder block shares a 90-degree cylinder angle and 4.400-inch bore centers. The LT1, LT4 and LT5 bore and stroke dimensions are 4.065-inches x 3.62-inches—the same as the LS3. Note: The L8T and L8P bore and stroke dimensions are 4.065-inches x 3.860-inches. Compared to the Gen IV versions, the Gen V’s (LT1, LT4 and LT5) aluminum cylinder block casting is all new but based on the same basic architecture. The L8T and L8P have a cast-iron block casting. It was refined and modified to accommodate the mounting of the engine-driven fuel pump and vacuum pump. It also incorporates new engine mount attachments, new knock sensor locations, improved sealing and oil-spray piston cooling. The oiling system is revised and features a new dual-pressure- control and variable-displacement vane pump with increased flow capacity. As with the Gen III/Gen IV engines, the oil pump is driven by the crankshaft. Variable displacement enables the pump to efficiently deliver oil flow as demanded. All Gen V engines feature oil-spray piston cooling, in which oil-spraying jets in the engine block drench the underside of each piston and the surrounding cylinder wall with an extra layer of cooling, friction-reducing oil. CAMsHAFT DEsIGN AND CAMsHAFT PHAsING As with the LS3, the LT1, LT4, LT5, L8T and L8P use a hydraulic roller- lifter camshaft. It is also located in the same position relative to the crankshaft as the LS3, but, importantly, the LT1, LT4, LT5, L8T and L8P camshafts features an all-new “trilobe” at the rear to drive the engine-mounted, high-pressure fuel pump for the direct-injection combustion system. There’s no such extra lobe on the LS3 camshaft, which negates cam swaps between the engines. Camshaft phasing (variable valve timing), which works with Active Fuel Management to enhance fuel economy, optimizes engine performance for given demands and conditions. Note: both the L8T and L8P are non-AFM. ROTATING AssEMBLY AND WINDAGE TRAY Within the LT engine block is a durable rotating assembly that includes a strong forged steel crankshaft and 6.098-inch-long, powder-metal connecting rods, as well as high-strength hypereutectic pistons. NOTE: LT4 and LT5 use forged aluminum pistons. Most LS3 production engines have an admittedly tough nodular iron crankshaft that is known to support high horsepower levels, even under higher boost levels. The crankshafts in C6 Corvette models with the Z51 handling package included a dry-sump oiling system that necessitated a longer crank snout to accommodate the unique oil pump. Those cranks were forged steel. The LT engines 6.125-inch connecting rod length is the same length as the LS3, but the profile of the rod itself is slightly different to enhance strength. As for the piston design, the LS3 features conventional flat-top design, while the LT1, LT4, LT5, L8T and L8P have a unique head topography that is essential to the direct injection system. The “bowl” and shape of the top of the piston head is designed to promote thorough mixing of the air and fuel. A dished center section helps direct the fuel spray from the injector, which protrudes into the combustion chamber rather than into the intake manifold on the LS3’s conventional port injection design. The crankshaft in the LT1, LT4, LT5, L8T and L8P is located with nodular main bearing caps, which is a significant upgrade over the LS3’s conventional gray iron main caps. They’re stronger and can better absorb vibrations and other harmonics to help produce smoother, quieter performance. They also maintain the optimal crankcase “windows” that were perfected on the LS3’s Gen IV architecture. 48 ChevroletPerformance.com Ls-sERIEs CRATE ENGINEs
