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A naturally aspirated V8 with a high-speed concept - Chevrolet is giving away the Corvette Z06 with the LT6-Engine made a unique but probably last appearance, a “free-aspirating V8 engine”.
The LT6 engine that is the new C8 Corvette Z06 will power in 2023 is as revolutionary as the LS1 engine was when it was introduced in 1997. Here we take a closer look at the inner workings of the LT6 engine and its specifications.
The definition of the American supercar
“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-engined Corvette and elevates it to provide refined but uncompromising racetrack capability with world-class performance. "
The Corvette Z06 is characterized by its motorized heart: the brand-new 5,5-liter DOHC-LT6, the most powerful naturally aspirated V8 that has ever come onto the market in a production vehicle. Let's take a look at the technology of the new V8 engine. One without supercharging and probably one of the last V8 engines to be developed.
The 2023 Z06 is a supercar for anyone who doesn't want to spend too much money on a supercar. Sure, with around $ 85.000 (US price) for the base model, a Z06 isn't cheap either - not in the sense of “cheap” - but when you consider that the Corvette is on a par with Porsche, Ferrari and CO and the like it can certainly be seen as a snapper among the super sports cars. There are hundreds of stories about what an amazing piece of technology the C8 Z06 is, but it's primarily about the engine. To the wildly pounding heart of the youngest Corvette. The drive that turns performance into passion.
New installation location - already used to it?
As everyone in the schoolyard knows by now, the engine of the C8 Z06 is behind the driver - a big change for the Corvette, a clever move by the developers. This installation position offers a lot of advantages in terms of driving feel, driving performance and race track handling. Now Chevrolet has decided to pull out all the stops with the Z06's engine as well. What is so special about the new engine, the LT6?
Well, at the top of the list is the crankshaft of the LT6 with 180 ° cranking (in contrast to the crankshaft of the LS and the previous LT with cross-plane-crank). This so-called “flat plane crank” changes, among other things, the entire sound spectrum of the engine. But not only. Although the crankshaft attracts a lot of attention, the LT6 has much more to offer than just an unusual (for an American V8) flat plane crank crank. For example, there is the completely new aluminum block, which still has the 4,4-inch hole spacing that is typical for the small block family. Or the new layout with two overhead camshafts and completely CNC-milled combustion chambers and intake ports. Then there is the mechanical “finger” valve drive and the double-bearing valve springs with intake and sodium-filled exhaust valves made of titanium. If this sounds familiar, then you probably remember the valves on the LS7 engine. Well, they have made the near perfect performance of this engine with forged pistons and titanium connecting rods their own.
How much power does the LT6 engine of the 2023 Z06 bring?
When you add it all up, you get the most powerful naturally aspirated engine ever built into a Corvette: 670 hp at 8.400 rpm (with a rev limiter at 8.600 rpm) and 625 Nm at 6.300 rpm should be enough to to be sure of all the attentions in the schoolyard of the super athletes. And no, the 8.600 revolutions per minute were not a typo, thanks to the super-light rotating body, the short stroke and the oversized cylinders, this US V8 actually rotates completely uninhibited up to 8.400 revolutions per minute.
While this LS6 engine appears “brand new” and fresh on the scene, the truth is that a version of this engine has been driving the Corvette C2019.R racing car since 8. All of these on-track tests helped engineers refine the LT6's performance and durability. When we first heard about the C8.R and found out that it was powered by a flat-plane crank, we speculated over a year and a half ago that GM would have to use this engine in a production vehicle due to the rules for Chevrolet Racing, and we rely on the Z06. We were right.
If you have a keen eye and look around the Z06's engine bay, you will find small spaceships molded into different parts. Was that an inside joke about the new Corvette Z06 going to be a rocket in 2023? Well, that would be a good guess, but in reality it was the design team that nicknamed the LT6 family of engines the Gemini. This is due to the use of two 87mm throttle bodies, two camshafts, two high pressure fuel pumps, and other cool parts. Nice to see they're still having fun at GM.
How does the active intake manifold on the LT6 engine on the Corvette Z06 2023 work?
The new active 11 liter intake manifold is another technical marvel. Active? Yes, due to the firing order of the new crankshaft, there are performance advantages through a physical method called resonance charging. This volumetric efficiency is used by a series of three valves that connect the two intake chambers. These open in different combinations in order to vary the effect of the pressure waves within the intake manifold or between the two chambers. When one of the 32 valves closes, a pressure wave is generated that moves up through the intake port. If you choose the “right” time, this wave will be reflected back down while the inlet valve is open. This returning wave rams a little more air into the party, which brings a little more power. If you want to find out more, google "Helmholtz resonance effect“That's the same principle.
How unique is the exhaust on the 2023 Z06?
A new engine required a new exhaust. The hard part about a flat-plane crank engine is that it can sound like two angry four-cylinder engines side by side; this is a problem that cannot be solved with a simple X-tube or other crossover tube. To get the sound right, a process that took two years, they started with the unique four-on-two-on-one stainless steel exhaust manifolds. Tubes of equal length flow into a unique and highly coordinated system that snakes through silencers placed in the corners of the car and exits in the middle through parabolic reflectors that send the music of the LT6 engine into the interior of the Z06. Like other GM models, the Z06 also has an active exhaust that masters all tonalities from loud on the racetrack to inconspicuously quiet. The result is a Ferrari-like scream, but with a slightly deeper tone. Chevrolet's tuning assistants set a delay on the direct injectors to create a few extra burps and pops when overspeed, but only when you have your foot on the accelerator. After all, sometimes too much of a good thing is still too much.
Funfact: When the pandemic brought GM to a standstill, work was stopped, but the computers kept checking the exhaust system design until they found the solution with the center exhaust. The sound was loved by everyone, but redesigning the rear apron to accommodate the center-mounted tailpipes cost millions, but in the end it was worth every penny.
How big is the deviation from the “norm” of the earlier LS and LT motors? Well, apart from what we mentioned earlier, the starter is located in the rear of the LT6 engine under the intake, while the alternator is in the same area but in front of the intake chambers. The area between the cylinder banks is quite narrow, as the two high-pressure fuel pumps with camshaft drive (optimized for operation at up to 9.000 rpm) are also located there. Another special feature compared to earlier engines are the injection nozzles, which are attached to the side under the exhaust valves. Not only has this created space for the huge active intake, it also mixes the fuel better.
The LT6 engine is hand-assembled by experts at the Performance Build Center at the Bowling Green, Kentucky assembly plant. The fitters work with precision tools and hand adjust the parts of the engine to meet Chevrolet's exact specifications. Each engine has a badge on the intake manifold with the signature of the technician who made it from start to finish.
Oil is life, and a robust oil system is of the utmost importance to an engine that is designed to be tough on the racetrack. In this area, the LT6 engine has learned a lot from its racing-ready C8.R cousin. Each pair of pistons is hermetically sealed off from the other pistons so that the air flows back and forth under the pistons with minimal pumping losses. The six-fold oil pump, which runs the entire length of the LT6, flushes each compartment along with the cylinder heads and requires 14 hp to operate. The system uses 10 liters of 5W50 and the large oil cooler is located in the rear intake on the driver's side. According to Chevrolet, temperatures should be between 250 and 265 degrees on a race day.
What is a flat plane crank?
When implementing a V8 engine, two basic crankshaft designs are available: cross plane and flat plane. Mostly, cross-plane cranks dominate, especially in American V8 engines, while flat-plane cranks are typically found in high-quality European exotic vehicles and racing cars. Cross-plane cranks give American muscle cars their unmistakable rumble, while flat-plane cranks give off a low howl at high speeds. But there's more to these cranks than just their exhaust sound.
Flat-plane cranks in V-8 and V-12 engines used to be rather rare and only found in very expensive super and hypercars. They are the reason that on a race day you could always tell whether a Ferrari was going to rev orgies. As the name suggests, all of the crank pins on a flat plane crank are in a single, flat plane. This is similar to a 4-cylinder in-line crank, but with more space for more connecting rods.
Do flat plane cranks have problems with vibrations?
Flat-plane cranks always switch from bank to bank regardless of the firing order. This provides optimal exhaust purging and eliminates the need for more complicated manifold primaries that need to move from one bank to another. Due to their design, they don't need large counterweights, which is why they weigh less and rev up faster. The disadvantage is that they suffer from secondary vibrations.
Chevy solved the vibration problem on the LT6 engine by minimizing piston speeds by opting for a large 4,11 "bore and a short 3,15" stroke. The result is a piston speed of 165 km / h at RPM (the 5.2L in the Shelby Mustang, for example, has a piston speed of 184 km / h). The vibrations were also due to the use of titanium piston rods from the Austrian company Pankl Racing Systems reduced. The aluminum balance shaft also helps combat flat-plane crankshaft vibrations. There is still some vibration, but nothing that could harm the car, the LT6, or the Corvette Z06's mission to be the baddest Corvette ever.