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