2023 Chevy Corvette Z06: A Deep Dive Into Its Awe-Inspiring New Engine
Nerd out with us as we dive into the nitty-gritty technical details of GM's LT6 flat-plane-crank V8. It could be the last of its breed.
Z06: Corvettes sanctified by those three characters are a rare breed. They're racetrack-bred apex predators capable of humiliating exotic cars that cost two or three times as much. The upcoming 2023 Chevy Corvette Z06 will continue this proud tradition of all-American whoop-ass, thanks in part to a new world-beating V8.
Small block or not?
Chevy's hand-built LT6 promises to be one of the most exciting power plants to debut in at least the last decade. As a race car engine turned loose on the street, this 5.5-liter unit is the most potent naturally aspirated V8 ever bolted between the fenders of a production car. Spinning to a jaw-dropping 8,600 rpm, this flat-plane-crank-equipped engine delivers a stunning 670 horsepower and 460 pound-feet of torque, all without the aid of any forced induction.
With figures like that, this engine's performance is not up for debate, but what you can argue about is its provenance. Carrying on a tradition dating back to 1955, GM engineers refer to the LT6 as a small-block engine. Yes, this new V8 shares the same 4.4-inch bore spacing as Chevy's classic "mouse motor" that was produced for decades, but other than this foundational measurement, everything is different.
In an online presentation detailing the ins and outs of the new LT6, Jordan Lee, GM's small-block global chief engineer, acknowledged that this is a unique engine, although he said, "We consider this the small-block Gemini." That codename is a nod to America's manned space program of the 1960s. It also references the twins Castor and Pollux of Greek mythology, which hints at the V8's flat-plant crankshaft that makes it run like a pair of conjoined four-cylinder engines. As another tip-of-the-hat to this heritage, no fewer than 54 stylized rockets are included on and inside this engine, little Easter eggs that can be found on the pistons, primary castings and elsewhere.
Lee and his team refer to the Corvette Z06's new engine as a small block, but he acknowledges others may not. He said this is something enthusiasts will likely argue about for years to come, but regardless of how you classify it, this engine is a whole lot of awesome.
The mission
The goal with this exotic V8 was to deliver thrilling on-track performance along with a unique sound and feel. "It had to be bespoke, it had to be dedicated to Corvette," said Lee, which is why this engine is so special and shares almost nothing with GM's traditional V8s.
Setting the LT6 apart from more pedestrian engines is its motorsports heritage. This power plant is essentially a roadgoing version of the LT6.R used in the Corvette CR.8 endurance race car. The block, heads, valve train and fuel-delivery system are all shared, although there are differences in packaging and performance.
Look how flat that torque "curve" is.
A displacement of 5.5 liters was chosen because it delivers good low-end torque. That lung capacity is provided by a 104.3-millimeter bore and a curt, 80-millimeter stroke, which, along with low-inertia rotating parts should allow the LT6 to rev with explosive speed. Despite a redline that's higher than low earth orbit, the torque curve is basically flat from about 3,500 rpm up to maximum engine speed.
Benchmarking the best
Before embarking on this development journey in 2014, GM engineers benchmarked a range of competitive power plants from rarified manufacturers like McLaren and Porsche. In particular, Lee said "we looked intently at Ferrari." In fact, his team even went on eBay and bought the engine from a wrecked Ferrari 458 Italia in Poland for $25,000.
Even though they intently studied the competition, Lee said, "This is a GM engine design that we've done completely in house," with no outside help as some have speculated. Aside from that 4.4-inch bore spacing, the LT6 is also clean-sheet design.
Even though it performs like something built by Ferrari or Lamborghini, "We maintained the traditional Chevy and Corvette value proposition," said Tadge Juechter, executive chief engineer of the Corvette. The LT6 has no extraordinary maintenance requirements. "You get the exotic engine but not the exotic ownership experience," he added, just change the oil and filter and check the spark plugs after 100,000 miles. Additionally, if needed, you should be able to get service at any one of hundreds of Chevy dealerships across North America. Try that with your Aventador.
The block and heads
It takes a lot of air to produce 670 horses au-naturel, which is why the LT6 has double-overhead camshafts and four valves per cylinder. Pushrods are nowhere to be found. The high-tumble intake ports are CNC machined and the combustion chambers are laser scanned for consistency.
These heads should flow massive amounts of air, exactly what you need to make huge horsepower.
The LT6's camshafts are made of hollow steel tubes to keep weight down, their forged, double-polished lobes are attached separately. Variable intake- and exhaust-camshaft timing is provided for a broader powerband. The bumpsticks' rotational motion is transferred to the valves through mechanical finger followers that have a wear-resistant diamond-like carbon coating and individual oil jets. Eschewing hydraulic lash adjusters reduces mass and more consistently controls the valves at high speeds, exactly what you need when driving the 2023 Z06 in anger. Curiously, no provision for adjusting lash is provided and there's no maintenance schedule. Thanks to proper materials selection, engineers tell me this isn't required and they've had no valve-train related issues during their extensive development work.
Allowing gas to flow into and out of the combustion chambers are 42-millimeter titanium intake valves and 35-millimeter sodium-filled nitrated-steel exhaust valves. Dual, straight-coil springs control those valves and help keep everything working as it's supposed to, even at 8,600 rpm.
Direct injectors squirt gasoline into the cylinders from the exhaust side of each head. This was done to avoid obstructing the intake ports. The LT6 features two high-pressure fuel pumps, one for each bank, both of which are driven by a separate shaft nestled in the engine's valley.
The aluminum block features a bedplate that supports the main bearings rather than individual caps. The block itself is cast with 22 sand cores, while the lower portion of the crankcase requires 25. Thin-wall, flangeless, gray-iron cylinder liners are pressed into the block, and when bored out to the right size, they're only about 1 millimeter thick, keeping weight down. Unusually for a street engine, the block is deck-plate honed, which accounts for any cylinder-wall distortion that may occur when the heads are bolted down, providing a more-accurate piston fit.
The valves are actuated by mechanical finger followers that should never need adjustment.
In order to reduce the castings' surface roughness for better oil flow, sand cores are coated with talcum powder before molten metal is poured into the molds. Special pathways cast into the block direct oil to the LT6's pumps, where the liquid gets sucked up by the dry-sump lubrication system.
The LT6 has seven oil pumps in total (!), six for scavenging and one supply pump. These keep the crankcase clear of oil that would cause parasitic drag on the rotating components. Ensuring everything is well lubricated, this engine takes 8 quarts of Dexos R 5W50 synthetic oil, which is stored in an external plastic tank. Don't worry about anything melting, that reservoir can continuously handle oil at a temperature of 374 degrees Fahrenheit.
The rotating assembly
The bits whirling around inside that fancy cylinder block are just as exotic. The LT6 features titanium connecting rods that are supplied by the same company that makes them for the C8.R. Rather than being located by the crankshaft, these components are piston-guided, which reduces friction and mass, helping make these parts more than 43% lighter than the connecting rods found in GM's LT4 V8.
Naturally, this engine's pistons are forged and they're gussied up with a friction-reducing polymer coating. Super-short skirts reduce weight and parasitic losses, while the pins are treated to a diamond-like carbon coating for enhanced durability
A flat-plane crankshaft is the heart of the Corvette Z06's new engine.
The heart of the LT6's rotating assembly is its forged-steel crankshaft. This flat-plane design, similar to those of exotic cars as well as the dearly departed Ford Mustang Shelby GT350, this part only needs four small counterweights opposed to the eight you'd find on a cross-plane crank. This, along with drilled main and rod pins, reduces mass, allowing the engine to rev faster. If you're curious (you've read this far so you must be, right?), the Z06's firing order is 1-4-3-8-7-6-5-2.
Induction and exhaust
The Corvette Z06's new engine breathes through a carefully designed intake system. An individual plenum serves each cylinder bank and is fed by an individual 87-millimeter throttle body. Each plenum houses four individual trumpet-shaped intake horns designed to minimize the imbalance between each cylinder. These runners give the incoming air a straight shot right into each combustion chamber, something that's necessary for making high-rpm power.
Between the LT6's plenums are a trio of 72-millimeter tuning valves. These open in different stages to adjust how air resonates in the manifold, providing more torque throughout the rev range. According to Eric Weir, LT6 design release engineer, GM's engineers ran through more than 50 different intake iterations, tweaking plenum volumes, angles and horn designs to get everything just right.
This is a cutaway of the 2023 Corvette Z06's exhaust system.
The C8 Z06 will feature a driver-adjustable exhaust system, one with continuously variable control valves, rather than more conventional flappers that have just two operating positions. This allows you to revel in flat-plane V8 music when desired and not wake the neighbors when you leave for work early in the morning.
A world-beating V8
With its high specific output, rev-happy nature and race-proven design, the new LT6 promises to be a real world-beater. GM didn't have to design a brand-new V8 from scratch, the automaker could have easily used its proven, supercharged 6.2-liter LT4 engine in the upcoming Z06, or even a retuned version of Cadillac's Blackwing V8, but neither of these would have been the right choice. "We tend to pride ourselves on purpose-built engines," said Lee, and to achieve their goals, he explained the Corvette required something special. In the case of Cadillac's twin-turbo V8, Lee noted it's a force-fed luxury-car engine with much smaller bores, elements that would not be optimal in a car designed for the track.
But a big question remains: Is an engine that redlines at 8,600 rpm going to last for hundreds of thousands of miles or will it vibrate itself to pieces as soon as the warranty expires? According to GM powertrain engineers, the LT6 is built to last, and even though that flat-plane crank does produce certain shaking forces, durability should not be an issue. Of course, there were some customer complaints about previous-generation Corvette Z06 engines having valve guide woes and other problems -- the automaker was even sued over this -- but engineers sound confident in what they've created here. Fingers crossed this new high-winding V8 is problem-free.
The new LT6 will be hand assembled at the Performance Build Center in Bowling Green, Kentucky. Trained technicians should be able to complete one of these engines in around three hours, including affixing a signed placard to a bridge between the intake plenums.
Look for this exhilarating V8 in the 2023 Chevy Corvette Z06, a car we at Roadshow cannot wait to drive. Given the gargantuan investments GM has made in electric vehicles, this could be the company's final internal-combustion hurrah. If that's the case, then GM is going out with a thermonuclear bang.
