Looking at the Gen 5 LT1 V-8 as a complete package, the specifications are impressive. With 6.2-liters of displacement, 11.5:1 compression, direct injection, continuously variable valve timing, active fuel management, variable displacement wet or dry-sump oil control, an advanced combustion system, and an estimated 450hp, the Gen 5 LT1 doesn't just set the bar, it becomes it. This is, without a doubt, the most advanced small-block engine platform that GM has ever designed and we believe the changes, both evolutionary and revolutionary, will continue to keep GM poised atop the sports car market well into the foreseeable future. However, the new engine design hasn't come without its fair share of criticism. Fans of single and dual overhead camshafts, along with the three- and four-valve-per-cylinder contingent, have already slammed GM's choice to retain an "archaic" cam-in-block, two valve pushrod design. And they may have a point, although the merits of the traditional small-block are hard to argue, if it wasn't for the massive amount of R&D that GM has poured into the Gen 5 design. No technology was spared, and none used for the sake of making headlines, in the new Gen 5 LT1. Each piece was selected, tested, refined, and tuned for maximum power in a lightweight, durable, robust, and efficient engine package. What the Gen 5 represents is a class leading 450/450 engine with all of the refinement you would expect from a world class design. And it'll reportedly propel the 2014 Corvette to 60mph from a dead stop in under 4-seconds, which will excite even the most cynical of techno-nerds. So, what's inside the new LT1 small-block? Let's dig in and find out.
Old Parts:Let's start our technical discussion with the parts that GM carried over from the Gen 4 engine design. Yep, that's all of them... A couple of bolts, the wrist pins, a retainer or two, and the LS3 locks. That's it. Literally everything else in the Gen 5 LT1 engine is brand new and was designed specifically for the new Gen 5 engine platform. This clean sheet approach wasn't about making things difficult for the aftermarket, it was about creating the most technologically advanced pushrod small-block V-8 ever produced and, in turn, one of the best sports cars in the world.
Direct Injection:The heart of the Gen 5 LT1 engine is the direct injection system. Unlike a traditional port fuel injection system (PFI), which introduces fuel into the air intake charge prior to the intake valve, direct injection works, as one could imply, by introducing fuel directly into the combustion chamber at exactly the right time. By precisely controlling the timing and pattern of the injected fuel, GM engineers were able to maximize "every drop of fuel" used within the combustion process, and this system is the primary contributor to the Gen 5's increased efficiency and power output. And, due to direct injection's unique cylinder cooling capabilities, GM engineers were able to increase compression to 11.5:1, while "recommending" but not "requiring" 93-octane fuel. The heart of the system lies underneath the composite intake manifold and places the injectors underneath the intake ports, suspended in the cylinder heads by the rail to isolate the injector pulses (and thus, noise). This unique "burying" of the system underneath the intake manifold allowed GM engineers to create a compact design, but equally important, a quiet system, which won't have the same noise and vibration issues of other similar systems. The injectors, which feature 6 holes each and specially designed injector spray and droplet patterns, have a flow rate of 125.7 lbs/hr at 1,450 psi, and can be fed up to 2,175 psi from the 1.48 cc/rev geometric displacement fuel pump. The pump is mechanical (fed by an electric in-tank unit) and is driven off the rear of the tri-lobe camshaft. Upgradability will remain the number one question from aftermarket enthusiasts.
Cylinder Heads and Valvetrain:Over 6-million hours of computational analysis went into the design of the new "advanced combustion system" found on the Gen 5 engine and one look at the cylinder heads proves it. Cast from 319-T7 aluminum, the Gen 5 LT1 cylinder heads feature large straight rectangular ports that incorporate a slight twist for the most efficient air tumble and maximum "mixture motion," compact combustion chambers, raised intake ports, and a centralized spark plug design. The 59cc chambers were designed specifically for the Direct Injection system (along with the AFM and CVVT camshaft) and feature reversed intake and exhaust valve locations, compared to the Gen 3/4, which significantly straightens the incoming air path into the combustion chamber. Large 2.130-inch (down from the LS3's massive 2.160-inch units) nitrided hollow intake valves paired with 1.59-inch hollow sodium-filled exhaust valves are present, actuated by stiffer 8.7mm pushrods and individually mounted 1.8:1 ratio non-offset common rocker arms. Along with the new intake and exhaust valve locations, the valvetrain has been further optimized with 12.5 and 12-degree valve angles (intake/exhaust, compared to 15-degrees found on the Gen 3/4), which have been splayed 2.5-degrees for increased airflow and reduced valve shrouding. The more centralized spark plug location promotes optimal ignition events by moving the flame closer to the center of the combustion chamber, which engineers cited as being "an essential enabler of the direct injection system's efficiency."
Camshaft:The Gen 5 LT1 camshaft features 200/207 degrees of duration at .050-inches, .551/.524-inches of lift, and a 116.5-degree lobe separation angle. These specs are quite similar to those found on the LS3 (204/211-degrees of duration, .551/.522-inch lift, 117 LSA) although the design has been optimized for the splayed valves, 1.8-ratio rockers, and the AFM system, and reversed for the new intake and exhaust valve locations. Unlike previous generations, the base LT1 will come standard with continuously variable valve timing (CVVT) and the ECM works with an oil-driven camshaft phaser to command up to 62 crank degrees of camshaft phasing. The rear of the Gen 5 camshaft is radically different from previous generations, with a tri-lobe designed lobe that drives the engine-mounted high-pressure direct injection pump. A new rear cam bearing was designed to work with the addition of the tri-lobe, although the overall position of the camshaft relative to the crank remains the same. Active Fuel Management is also new to the Gen 5 and special AFM lifters are present on cylinders 1, 4, 6, and 7. Both electronically and hydraulically controlled, the AFM system shuts down 4 of the 8 cylinders under "low load" conditions, which saves gasoline and increases the effective MPG rating of the LT1. Surprisingly, and somewhat counter intuitively, the large 6.2-liters of displacement is helpful here, with the engine running on 3.1-liters in AFM mode, enabling it to power the Corvette effortlessly under many light load conditions. If the engine was smaller, say 5.5-liters as many had hypothesized, AFM would run at 2.25-liters, which likely would have been difficult to maintain in many driving situations.
Engine Block:While much of the Gen 5 engine design is revolutionary, the engine block is more evolutionary, taking much of its architecture from the Gen 3/4 engine, with some key changes in just the right places. Cast from 319-T7 aluminum (identical to the cylinder heads), the Gen 5 block features cast-in-place liners, an all aluminum deck face surface (cast over liners), new water jackets for an optimized structure, and mounting provisions for the high-pressure camshaft actuated fuel pump. Inside, the Gen 5 has been strengthened substantially with new nodular iron main caps instead of conventional powdered metal units. Affixed to the block with 6 main bearing bolts-per-cylinder, including the two cross bolts, the nodular main bearing caps are stronger, reduce crankshaft flex, and can better absorb undesirable harmonics and/or vibrations, which increases engine reliability and overall smoothness. Cylinder head sealing has been improved through the use of an all aluminum deck surface (cast over liners) and the inclusion of M12 cylinder head bolts. The block also comes standard with internal oil squirters, a la the LS9/A, and an optimized crankcase for improved windage control. Externally, the block sports new mounting bosses, revised knock sensor locations, and a new rear cover design. The oil pan remains an integral part of the block's strength.
Rotating Assembly:Forged from high strength eutectic aluminum alloy, the Gen 5 LT1 pistons feature unique faces that were "optimized via extensive analysis to precisely direct the fuel spray for a more complete combustion." Long gone are the flat top slugs found in traditional Gen 3/4 engines, replaced instead with extremely accurately machined high compression "pop-up" pistons that feature a specific Direct Injection "fuel bowl," and valve reliefs (intake and exhaust) for proper piston-to-valve clearance during camshaft phasing. The ring package is similar to those found on Gen 4 LS3 pistons and the oil drains are too, although they are cast and drilled for the Gen 5. The 6.125-inch connecting rods have been optimized as well, built from powdered metal and designed to be both lightweight and strong. The piston pin end is wide and tapered, while the crankshaft end has been lightened around the bolt location. The Gen 5 crankshaft is forged from a 1538MV twisted steel and features induction hardened journals along with intermediate pin drills. Like the Gen 4, the Gen 5 utilizes a 58X reluctor wheel for extremely accurate ignition control.
Both the crankshaft and connecting rods ride on all new Polymer Coated Bi-metal eccentric bearings, which have passed GM's grueling testing, including the brutal "hot scuff" test, in which a brand new, never fired engine is run at wide-open throttle with zero break-in period. In fact, all of GM's testing is brutal, with the Gen 5 LT1 completing the equivalent of over 1.5 million miles of validation testing. The upper thrust bearings are also new, with a 3-piece, 180-degree washer design that is laser welded during assembly for maximum strength and longevity.
Oil control:The heart of the all-new Gen 5 small block oiling system is a crank driven, variable-displacement, dual-pressure oil pump, which continuously adjusts oil flow to maintain proper oil pressure at the bearings. Working with the AFM system, the variable-displacement pump keeps oil pressure "efficient" during low RPM operation and ramps it up to higher pressures as RPM and demand increases. The Corvette engineering team has seen a 7-10psi decrease in oil pressure thanks to the new system when compared to the LS family, and has revised the oil pressure sensor location, moving it from the back to the front of the block. Piston oil squirters are standard on the Gen 5 LT1 engine and are activated "only when they are needed most." This includes initial engine start-up and at higher RPM, when piston cooling and additional durability is required. A two-stage dry-sump system will also be offered, which is also driven by a new variable vane oil pump, along with a new high output scavenge pump. Both wet and dry systems feature enhanced windage trays, featuring a new oil scraper design, and oil pan designed for increased oil control and reliability under high-G conditions. And if you're having a hard time believing how good this system really is, check out the video of an LT1 running on a GM Tilt Rig (www.youtube.com/user/gmhightechmag), which can simulate up to 1.3g of lateral acceleration and over 53-degrees of engine tilt.
Along with the improved oiling system, the Gen 5 engine also incorporates an all-new patent-pending integrated positive crankcase ventilation (PCV) system. This system works to reduce oil consumption (thus increasing oil life) by separating oil and air with up to 3-times the efficiency found in the Gen 3/4 engines. The new valve covers feature baffled domes between each coil to separate oil found in the crankcase from air, while the AFM solenoids feature revised "foul air separators" for similar reasons.