Inside GM’s all-new 6.2-liter Gen 5 LT1 Small-Block

A comprehensive look at the direct-injected heart of the 2014 Corvette

Justin Cesler Oct 26, 2012 0 Comment(s)
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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.

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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.

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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."

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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.




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