Later this year, Chevrolet will push out the seventh-gen Corvette powered by the fifth-gen small-block Chevy V8 (Gen V LT1). The all-new engine revives the historic LT1 name and promises at least 450 hp and 450 lb-ft of torque from the same 6.2L (376ci) displacement of the current LS3, only with greater efficiency. In fact, Chevrolet says it will top the already impressive 26-mpg highway rating of the current Corvette.
We're sure just about everyone reading this magazine doesn't give a Prius about fuel economy in a Corvette, but the technologies employed to achieve it should interest you—especially if you plan to modify or tune the Gen V LT1. They include direct injection, active fuel management (AFM), and continuous, variable valve timing. An all-new combustion system was developed to optimize those technologies, although it is the primary supporter of the direct injection fuel system. There's also an all-new "E92" controller directing the combustion festivities.
"The new Corvette's LT1 represents the most significant redesign in the small-block's near 60-year history," Sam Winegarden, GM's vice president of global powertrain engineering, told the media at the engine's unveiling. "More than just great horsepower, the Gen V LT1 has been optimized to produce a broader powerband. Below 4,000 rpm, the torque of the Corvette LT1 is comparable to that of the LS7 out of the current Corvette Z06. The LT1 is a sweetheart of a powerplant, and drivers will feel its tremendous torque and power at every notch on the tachometer."
That's terrific, but as the kids say these days, "Will it drift?" In other words, will the new LT1 be as friendly to tuning and power-adders as the previous two generations of LS engines? That remains to be seen, but without a doubt its new technologies will pose significant challenges—not the least of which is the direct injection system.
As its name implies, direct fuel injection introduces fuel directly into the combustion chamber rather than into the intake manifold with a conventional port-injection system. It enables greater combustion efficiency with a more complete burn of the air/fuel mixture. This is achieved by precisely controlling the mixture motion and fuel-injection spray pattern. Direct injection also keeps the combustion chamber cooler, which allows for a higher compression ratio—a stout 11.5:1 .
Although GM engineers have several years' worth of direct-injection experience under their belts, it has all been with dual-overhead camshaft engines. Designers had to start from scratch for the Gen V LT1, as the two-valves-per-cylinder arrangement was completely different from the DOHC designs. In fact, the flow field—the motion of the air/fuel mixture—is more complex with a two-valve design, and direct injection requires more mixture swirling for optimal combustion.
More than 75 iterations of combustion systems for the Gen V were evaluated through literally millions of hours of computational analysis before selecting the final design. The result is an all-new cylinder head and a new dished-piston configuration. They work cohesively to exploit the high-compression, lean-mixture parameters enabled by direct injection. Smaller 59cc combustion chambers complement the dish volume of the pistons' heads, while the pistons also feature "risers" at the top to direct the fuel spray for a more complete combustion. Also, the spark-plug angle and depth have been revised to protrude farther into the chamber, placing the electrode closer to the center of the combustion to support the direct-injection system.
An engine-driven fuel pump supports the direct injection and is a game-changer for the Gen V small-block. Although it is supported by a conventional pump in the fuel tank, the engine-driven pump is actuated by three extra lobes on the camshaft. The pump is mounted in the valley between the cylinder heads beneath the intake manifold, feeding a set of very specialized fuel injectors with super-high pressure of about 2,175 psi. It is this fuel-delivery system that has huge implications for the aftermarket performance and tuning world.
Another significant change is the reversal of the position of the intake manifold and exhaust valves compared with the Gen IV small-block. The change, which is supported by an all-new intake manifold, enables a straighter path for the air charge into the combustion chamber. The airflow enters the combustion chambers via large, 2.13-inch (54mm) hollow-stem intake valves and exits through 1.59-inch (40.4mm) hollow-stem/sodium-filled exhaust valves. The valves are held at new, 12.5-degree intake/12-degree exhaust angles, versus the Gen IV's 15-degree angle, and they are splayed slightly to reduce shrouding and enable greater airflow.
The camshaft features a phaser module on the front for variable valve timing, and a tri-lo
A sculpted piston head is an integral component of the direct-injection system and undergo
LT1 (bottom) and LS3 heads compared. Note the exhaust-port shape difference, along with th
Combustion-chamber view shows protrusion of the spark plug, reversal of the tradition valv
Cylinder Deactivation and Variable Valve Timing
Along with direct injection, the Corvette employs active fuel management (AFM) for the first time. That's GM's term for cylinder deactivation technology, which shuts down half of the cylinders in light-load driving to save fuel. Yes, that technically means a C7 may cruise down the freeway as a four-cylinder, but the inherent torque of the big-displacement, 6.2L engine and seamless switching between V4 and V8 modes makes the phenomenon essentially imperceptible.
As for the continuously variable valve-timing system, a vane-type phaser on the front of the camshaft changes its angular orientation relative to the sprocket, thereby adjusting the timing of valve operation on the fly. It is a dual-equal, 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. At idle, for example, the cam is at the full advanced position, allowing exceptionally smooth idling. Under other conditions, the phaser adjusts to deliver optimal valve timing for performance, driveability, and fuel economy. Under a light load, it can retard timing at all engine speeds to improve fuel economy.
The fuel rail assembly is fed by the engine-mounted, high-pressure fuel pump (arrow) deliv
New Block Casting, Oiling System, and More
The Gen V's cylinder-block casting is all new but based on the same basic architecture as the previous LS engines. It was refined and modified to accommodate the mounting of an engine-driven, direct-injection, high-pressure fuel pump. It also incorporates new engine-mount attachments, new knock-sensor locations, improved sealing, and provisions for oil-spray piston cooling.
The LT1's oiling system—including oil-spray piston cooling—is also optimized for improved performance. It is driven by a new, variable-displacement oil pump that enables more efficient oil delivery, per the engine's operating conditions. Its dual-pressure control enables operation at a very efficient oil pressure at lower rpm coordinated with active fuel management and delivers higher pressure at higher engine speeds to provide a more robust lube system for aggressive engine operation. A dry-sump oiling system will be available.
Another distinctive LT1 feature is domed rocker covers, which house a unique, integrated positive-crankcase-ventilation (PCV) system that enhances oil economy and oil life while reducing oil consumption and contributing to lower emissions. The rocker covers also hold the direct-mount ignition coils. Between the individual coil packs, the domed sections of the covers contain baffles that separate oil and air from the crankcase gases—about three times the oil/air-separation capability of the LS3.
Additional engine features include a "four-in-one" short-header exhaust manifold design that is very similar to the efficient, low-restriction LS7 design and a revised cooling system with an offset water pump that enhances efficiency.
All-new intake manifold has a “runners-in-a-box” internal design that complements the head
58 Years of Heritage and No Excuses
In the sports-car world, much will be made about the decision to retain a cam-in-block/overhead-valve configuration for the Corvette's engine when the rest of the competition has long been running dual-overhead cams. The inherent torque of the pushrod design, along with the less complex and more compact packaging for the small-block are important considerations, too. The low-slung hoodline of the Corvette wouldn't be possible if LS engine sported mile-wide and tall DOHC hardware.
High-performance tuning implications notwithstanding, what we've seen of the new LT1 engine demonstrates the General has nothing to apologize for, and the best tag line for the next Corvette might simply be, "Bring it." Hell, the C6.R racing team decimated the competition in its production-based class in the American LeMans Series in 2012, winning the points championship by driving its low-tech pushrod engines past the high-tech hardware of Ferrari, Aston Martin, and others.
We can't wait to experience the new LT1 in the C7 Corvette—and we're even more interested in what tuners will be able to do with it on the second day. Stay tuned.
New variable-displacement oil pumps are used to enhance efficiency. This is the pump assem
“Four-in-one” exhaust header design is similar to the LS7’s, although in cast iron versus
Testing for the LT1 included countless hours of continual wide-open blasts between peak to
|2014 Corvette LT1 6.2L V8 Specifications
||90-degree V8 with overhead valves; continuous VVT
||6.2L (376 ci)
|Bore x stroke (in/mm)
||Cast aluminum with nodular main caps
|Main bearing fasteners
||Six, including two cross bolts per cap
||Powder metal, 6.125 inches long
||Eutectic aluminum alloy
||319-T7 cast aluminum with 59.02cc combustion chambers
|Valve angles (degrees)
||12.5 intake, 12 exhaust
||2.13 inches (54mm) hollow
||1.59 inches (40.4mm) hollow sodium
||Hydraulic-type with tri-lobe for fuel-pump drive
||0.551-inch (14mm) intake / 0.524-inch (13.3mm) exhaust
||200-degrees intake/207-degrees exhaust (at 0.050-inch)
|Lobe separation angle
||"Runners-in-a-box" design; composite construction
||87mm electronically controlled throttle-body
||58X with individual coil-on-plug and iridium-tip spark plugs
|Max. engine speed
||6,600 rpm (fuel cutoff)