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 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. Dubbed EcoTec3 in the new trucks, including a 4.3L V-6, 5.3L V-8 and 6.2L V-8, and carrying historic “LT” designations in the Corvette, 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. 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 accommo- date an engine-driven high-pressure fuel pump for the direct-injection system. As builders adapt the LT1 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: 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’s bore and stroke dimensions are 4.06-inches x 3.62-inches—the same as the LS3. Compared to the Gen IV versions, the Gen V’s aluminum cylinder block casting is all new but based on the same basic architecture. 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. All Gen V LT1, LT4 and LT5 engines use the same block as a foundation. CAMSHAFT DESIGN AND CAMSHAFT PHASING As with the LS3, the LT1 uses a hydraulic roller-lifter camshaft. It is also located in the same position relative to the crankshaft as the LS3, but, importantly, the LT1’s camshaft 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. For the record, the LT1 camshaft’s specifications lift include: 0.551/0.524-intake/exhaust lift, 200/207 degrees intake/exhaust duration at 0.050 tappet lift and a 116.5-degree lobe separation angle. The LS3’s cam specs are: 0.511/0.525-inch lift, 204/211 degrees duration and a 117-degree lobe separation angle. Camshaft phasing (variable valve timing), which works with Active Fuel Management to enhance fuel economy, optimizes engine performance for given demands and conditions. A vane-type phaser is installed on the front of the camshaft to change its angular orientation relative to the sprocket, thereby adjusting the timing of valve operation on the fly. It is a cam phasing system that adjusts camshaft timing at the same rate for both intake and exhaust valves. The system allows linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (horsepower per liter of displacement) without sacrificing overall engine response or driveability. It also provides another effective tool for controlling exhaust emissions. The vane phaser is actuated by hydraulic pressure and flow from engine oil and managed by a solenoid that controls oil flow to the phaser. ROTATING ASSEMBLY AND WINDAGE TRAY Within the LT1 block is a durable rotating assembly that includes a strong 1538MV forged steel crankshaft and 6.098-inch-long, powder-metal connecting rods, as well as high-strength hypereutectic 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. If you order the production-based Chevrolet Performance LS3 crate engine (P/N 19435098) you’ll get the standard oil pump and cast crankshaft. The LT1’s 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 has 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 Small-Block 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. A redesigned windage tray is also used with the LT1, which features a unique oil scraper designed to enhance performance and efficiency by improving oil flow control and bay-to-bay crankcase breathing. CYLINDER HEAD DESIGN The Gen V’s all-new cylinder head design builds on the excellent, racing-proven airflow attributes of previous Small-Block heads. Its all-new direct-injection combustion system supports tremendous airflow at higher rpm for a broad horsepower band, along with strong, low-rpm torque. 58 CHEVROLETPERFORMANCE.COM LS-SERIES CRATE ENGINES
