Tony Roma, now the Corvette’s executive chief engineer, still remembers signing off on the final “stock test” of a new LS6 engine back in 2001. The dynamometer certification of that amped-up V-8, which ably powered the C5 Z06 and, later, the Cadillac CTS-V, confirmed a husky 385 horsepower and 385 pound-feet of torque. (Those numbers jumped to 405/400 in the Z for ’02.)
A quarter-century later, a reborn LS6 will help the 2027 Grand Sport outpunch not only that Z06 forebear, but also the C6 Z06. That famously boisterous Corvette generated 505 horsepower and 470 pound-feet of torque from its 7.0-liter LS7 V-8.
“We love taking those storied, old engines and just squashing them,” Roma says with a laugh.
When the 1955 Corvette became the first recipient of a small-block Chevy V-8—in tandem with the Chevy Bel Air—693 of 700 buyers that year chose the optional, 265-cubic-inch engine over the wimpy Blue Flame inline six. The Corvette was finally on its way to becoming a legitimate sports car, rather than a pretty pretender.
The new LS6 boasts 6.9 liters and 409 cubic inches. The latter figure evokes another famous number from Chevy history: the “W-Series” big-block in the Impala Super Sport that inspired The Beach Boys’ hit “409.” (She’s so fine, indeed).
The LS6 is just the sixth entirely new small-block in GM history. Its engineering signatures can be found on more than 100 million examples built since 1955, including the 4.4-inch cylinder bore centers repeated on this large-displacement “SBC.”
“Those bore centers are a big part of small-block heritage,” says Mike Kociba, assistant chief engineer for the LS6.
With 535 horsepower and 520 pound-feet of torque, the LS6 generates more torque than any naturally aspirated GM V-8 in history.
“We’re trying to recreate some of what worked in the muscle-car era,” Kociba says. “We wanted a wide, high torque band and high power. It feels like we’re bringing a piece of Americana back.”
Yet no classic muscle-car engine could touch the new LS6’s might, or its emissions and fuel economy that actually benefited from an enlarged displacement versus the C8’s 6.2-liter LT2. Despite gains of 40 horsepower and 50 pound-feet, the LS6 is 6-percent more fuel efficient. That’s all aided by “displacement on demand” tech that became critical to meet emissions targets during development.
The pushrod engine appears an engineering masterwork, with an improbable 13:1 compression ratio, forged pistons, and a sophisticated blend of high-velocity intake ports and direct fuel injection.
The engine that started a revolution, the 1955 Chevy small-block.
The new V-8 gets a longer stroke compared with that LT2, at 100mm versus 92mm. Both engines peak at an identical 6,600-rpm redline, Kociba notes, yet the LS6’s longer-traveling pistons are actually flying much faster and undergoing more stress. That called for forged pistons and connecting rods. And without modern engine controls and digital development, Kociba says, the V-8 would never have expanded to those nostalgic, 409-cubic-inch heights.
“We were going to make it ‘only’ 6.6 liters,” Kociba says. “But then we started playing around and realized that, by adding two millimeters to the stroke, we get more performance without compromising anything else. In the past we might not have explored that.
“A large-displacement V-8 is what customers want, and we’re going to give it to them.”
A sky-high 13:1 compression ratio even manages to beat the cylinder squeeze of the fearsome, 427-cubic-inch L88 of 1967-1969. And that vintage big-block mill was purpose-built for racing, with a minimum recommended fuel octane of 103.
“That engine was 12.5:1 compression on leaded fuel,” Kociba says. “The only way we could pull off beating that today, with unleaded, was with our advanced controls.”
At Spring Mountain Motor Resort in Nevada, Kociba walks me around a red-headed LS6 that’s perched on an engine stand, the better to see its towering “tunnel ram” intake manifold and 95mm throttle body, the latter item 9 percent larger than the LT2’s. As on an LT2, dry-sump oiling with three scavenge pumps allows for a shallow pan that lets the engine sit lower in the engine bay. High-velocity ports feed a fuel system than runs a combo of port and direct injection, akin to the C7 ZR1’s LT5 V-8.
Oil and cooling systems are lavishly reworked, including dual oil feeds for the bottom end. That ensures the crankshaft doesn’t have to make a full revolution before the connecting rods get a fresh splash of cooling-and-lubricating oil. Two-piece water jackets in the cylinder head protect the valvetrain, with cross-flow cooling to effectively soothe the hottest spots inside cylinders. Modern simulations helped prove that a smaller intake port actually improved combustion, power, and efficiency, while creating a broader, less-peaky torque curve.
Combined with the tunnel-ram intake, “You’re speeding the air so it can get down and fill every nook and cranny of the cylinder,” Kociba says. “And the tunnel ram is a huge enabler of that 13:1 compression ratio.”
Keith Badgley, lead development engineer, says the inner workings of the LS6 are critical to its wicked soundtrack. Even standing still, there’s no mistaking the high-decibel wallop of the LS6, including raspy midrange frequencies that rattle my eardrums during a static demonstration.
“You’re hearing the bigger displacement, the cam, the compression,” Badgley says. “You get the deep acoustics for sure, but we had so much tonal range to work with.”
The LS6 produces enough sound to create its own sonic weather system—one part thunder, one part crackling lightning. Since nearly 90 percent of C8 customers were choosing the optional performance exhaust, the Grand Sport makes it standard. If you said that soundtracks are important to Corvette owners, you’d be spot on.
Both the Grand Sport (left) and Grand Sport X use the LS6 for 2027, as does the base C8 Stingray. As previously reported, the E-Ray has been discontinued.
We’re all grinning like school kids when we hear the LS6’s Marshall-stack thunder, played through the Grand Sport’s optional, single-center exhaust outlet. Trust me: The crackling, carnivorous sound will be pure catnip to Corvette fans, including buyers who go all out for the 721-horsepower Grand Sport X hybrid.
The LS6 “pushes 409 cubic inches of jackhammer fury through the tailpipes,” Kociba says. “The pulses from the engine are just so powerful, running down that ‘tri-Y’ exhaust layout.”
Then there’s the Grand Sport X, which adds an electrified hybrid jolt to the new V-8 to reach supercar-level heights of power and performance. Paired with the shrieking LS6, those electrified front wheels create a tag-team of rowers that might impress Charlton Heston’s Ben Hur.
Josh Holder, Corvette chief engineer, explains what a mythical creature from Brazilian folklore has to do with a Corvette. GM dubs its latest engine-management system “Encantado,” which refers to a shape-shifting river dolphin that transforms into a handsome human. Here, GM’s system integrates machine learning to both speed up testing and improve performance based on real-world data collection. It’s the first V-8 application of this new GM software.
Regarding the LS6 name, Kociba says customers will instantly identify this as a high-performance Chevy engine. The “LS” also nods to the port fuel injection of fourth-gen small blocks, with the “6” dovetailing with the sixth-generation of this 72-year-old engine family. (We suspect that any associations drawn with the legendary, 454-ci LS6 big-block of 1971 are purely intentional as well.)
Apparently, with an engine this good, Grand Sport fans will have to share. The LS6 also becomes the standard powerplant in the 2027 Stingray. I ask Roma if that might take a bite out of Grand Sport sales, since Stingray customers can now choose the upgraded engine without having to pony up the $15,000 price premium separating the two models. Roma feels it’s not an issue, and that the Grand Sport’s wide-body design and additional performance tweaks will make it a compelling upgrade.
He says the engine’s development timing neatly coincided with the Grand Sport’s planned arrival, “making the car truly epic.” But denying it to the Stingray didn’t make sense, he says, even for a single model year.
“We wanted this engine to be attainable for Stingray customers as well,” Roma says. “We spend a lot of time thinking about which customer is buying each model, and why. You can end up with too many combinations if you’re not careful. And ultimately, this is a team sport.”
Holder adds that a stand-alone engine for the Grand Sport would introduce too much cost and manufacturing complexity. For one, Chevy didn’t want to obtain regulatory certification for an engine that would power a single niche model.
“You might spend $10 million just to certify an engine, so it becomes something that needs to go across the lineup,” Holder says.
Kociba notes the LS6 will be assembled by GM’s Flint Engine Operations in Flint, Michigan, about an hour north of Detroit. Small-block production returns to the city where the first Corvette V-8s were built in 1955. The latest C8s are coming full circle, and faster than ever.
