The LT6 engine that will power the new 2023 C8 Corvette Z06 is as game changing as the LS1 was when it was introduced in 1997. Bold statement? Yep, but once you delve into the guts of the LT6, and look at its specifications, that opening claim may end up being somewhat of an understatement.
"The new Corvette Z06 defines the American supercar," said General Motors President Mark Reuss. "It builds on the distinctive design and groundbreaking dynamics introduced with the mid-engine Corvette and elevates them to deliver refined but uncompromising track capability with world-class performance."
The Z06 is set apart by its beating heart: The all-new 5.5L DOHC LT6, the highest-horsepower naturally aspirated V-8 to hit the market in any production car—ever. As hot rodders, we're thinking in terms of salvaged swaps and crate engines, so let's take a deeper dive into this very cool bleeding-edge V-8.
The 2023 Z06 is a supercar for those without supercar-sized wallets. Yeah, at around a $85k for the base model, it isn't cheap, but considering that it's on par with Lambos, Ferraris, and the like, it certainly falls on the more affordable side of the ledger. There are tons of stories out there about what an amazing hunk of engineering the C8 Z06 is, but we're here to talk about what motivates it down the highway and around your favorite road course: the revolutionary LT6 engine.
As you all know, the C8's mill resides behind the driver, a huge change for Corvette, but one that provides a ton of performance and handling benefits. Chevrolet decided to pull out all the stops on the Z06's engine. What's so cool about the LT6? Well, top of that list would be the LT6's flat-plane crank (as opposed to the LS and previous LT's cross-plane crank). While the crank gets lots of attention there's far more to this LT6 than just a unique (for an American V-8) crank. Things like an all-new aluminum block that still has the small-block family's signature 4.4-inch bore spacing. Or the new dual-overhead cam layout with fully CNC-machined combustion chambers and intake ports. There's also the mechanical "finger follower" valvetrain and dual-coil valve springs with titanium intake and sodium filled exhaust valves. If that sounds familiar, then you most likely remember those valves from the LS7 engine. Well, they borrowed from the near perfection of that engine with forged pistons and titanium connecting rods as well.
Add this all up and you end up with the most powerful naturally aspirated factory engine ever stuffed into a Corvette: 670 hp at 8,400 rpm (with an 8,600-rpm redline) and 460 lb-ft of twist at 6,300 rpm should be enough to get anyone's attention. And, no, the 8,600-rpm part wasn't a typo, thanks to the super-lightweight rotating guts, short stroke, and oversquare cylinders.
While this LS6 seems "all new" and fresh on the scene the truth is that a version of this engine has been powering the Corvette C8.R race cars since 2019. All that on track testing helped engineers refine the LT6's performance and durability. When we first heard the C8.R and figured out it was running a flat plane crank we speculated, over a year and a half ago, that due to the rules governing Chevrolet Racing that GM would have to field this engine in a production car and our bets were on the Z06. We were right, and you can read that prediction here.
If you have a keen eye, and look around the engine bay of the Z06, you'll find little rocket ships cast or molded into various parts. Was this an inside joke about how the new 2023 Corvette Z06 will be a rocket? Well, that would be a good guess, but really it was the design team giving the LT6 engine family the nickname Gemini. This is due to its use of twin 87mm throttle bodies, twin cams, twin high-pressure fuel pumps, and other pairs of cool parts. Nice to see they are still having fun over at GM.
The new 11-liter active split intake manifold is another engineering wonder. Active? Yeah, you see due to the firing order of the new crank there were performance benefits from a physics deal called resonance supercharging. This volumetric efficiency is leveraged by a series of three valves that connect the two intake plenums. These open in different combinations to vary the effect the pressure waves within the plenum or between the two plenums. When one of the 32 valves closes it generates a pressure wave that travels back up the intake runner. If you time it "just right" that wave reflects back down while the intake valve is open. This returning wave rams a bit more air into the party, which makes a bit more power. If you want to learn more then Google "Helmholtz Resonance Effect," which is the same principal.
A cool new engine necessitated a cool new exhaust. The hard part with a flat-plane crank is that it can sound like two angry four-cylinder engines next to each other; it's a problem that can't be solved with a simple X-pipe or other crossover tube. To get the sound right, a process that took two years, they started with the unique four-into-two-into-one stainless steel exhaust headers. Equal-length pipes feed into a unique and highly tuned system which winds through mufflers, stuffed in the corners of the car, and exits out the middle through parabolic reflectors which sends the LT6 engine music toward the Z06's cabin. Like other GM offerings the Z06 has an active exhaust which can be anything from crazy loud to stealthy quiet. The result a Ferrari-like scream, but with a somewhat deeper tone. The tuning wizards at Chevrolet set a delay for the direct fuel injectors to encourage a few extra burps and pops on overrun, but only while your foot is moving the throttle. After all, too much of good thing is sometimes still too much.
Fun fact: When the pandemic shut GM down all the work stopped, but the computers kept rehashing the exhaust system designs until they determined the center-exit solution. The sound was loved by all but redesigning the rear fascia to house the centrally mounted reverse-megaphone tips cost millions, to us it was worth every penny.
How big of a departure from the "norm" of previous LS and LT engines? Well, aside from what we've already mentioned how about how the starter is mounted in the rear of the LT6's valley beneath the intake while the alternator lives in the same valley but to the front of the mill. The valley is pretty crowded since it also houses the twin high-pressure cam-driven (optimized for 9,000-rpm operation) fuel pumps. Another oddity compared to previous engines are the injectors which are side mounted under the exhaust valves. This not only made room for the huge active intake, but it also mixes the fuel better.
The LT6 engine is hand-assembled by master engine builders at the Performance Build Center within the Bowling Green Assembly Plant in Kentucky. Builders use precision tooling and hand fit pieces of the engine to meet Chevrolet's exact specifications. Each engine features a plaque on the intake manifold with the signature of the technician who crafted it from start to finish. A visit to this plant is high on our list of things to do.
Oil is life and to an engine designed for hard road course life a robust oiling system is of upmost importance. In this area, the LT6 engine learned a lot from it's C8.R race-bred cousin. Each piston pair is hermetically sealed off from the other pistons so that the air under the pistons simply back and forth with minimal losses from pumping. The six-bay oil pump, that runs the length of the LT6, scavenges each bay, along with the cylinder heads, and takes 14 hp to operate. The system uses 10 quarts of 5W50 and the rather large cooler is housed in the driver side rear intake. According to Chevrolet track day temps should stay around 250 to 265 degrees.
There are two crank designs available when picking one for your next V8 project: cross- and flat-plane. For the most part cross-plane cranks dominate, especially in American V-8 engines, while flat-plane cranks typically show up in high-end Euro exotics and full-on race cars. Cross-plane cranks give American muscle its distinctive rumble while flat-plane cranks have a tell tail high-rpm whine. But, there's more to these cranks than just their exhaust notes.
Flat-plane cranks, in V-8 and V-12 engines, used to be fairly rare and only seen in uber-expensive super- and hypercars. They're the reason you can always tell a Ferrari is ready to crest the hill at a track day. Just like the name states a flat-plane crank has all its crank pins in a single, flat plane. This is much like an inline 4-cylinder crank, but with more space for more rods.
Flat-plane cranks, no matter what firing order they have, will always alternate from bank to bank. This yields optimum exhaust scavenging and thus doesn't require the more complex header primaries that have to cross over from one bank to the other. Due to their design they don't need huge counterweights, which is why they weigh less and rev up so quickly. The downside is that they suffer from secondary vibrations.
Chevy solved the vibration issue with LT6 engine by minimizing piston speeds, by opting for a large 4.11-inch bore and short 3.15-inch stroke. The result is a 103-mph peak piston speed at redline (for example a the 5.2L in the Shelby Mustang has 114 mph piston speed). Vibration was also helped by the use of titanium piston rods from Austria-based Pankl Racing Systems. Even the aluminum harmonic balancer helps in the battle to solve flat-plane crank vibrations. There are still some vibrations, but nothing detrimental to the car, the LT6, or the Corvette Z06's mission to be baddest Corvette ever built.
When equipped with the Z07 performance package in the track prepared configuration on a 300-foot diameter circle, the car is capable of 1.22 g of road-hugging grip.
Photos By Jason Lanham and Shawn Mangenje - Astro Creative and courtesy of General Motors