The LT6 engine of the 2023 Chevrolet Corvette Z06 is not only the world’s largest flat crankshaft V-8, but also the world’s most powerful naturally aspirated mass-produced V-8, surpassing the 622 horsepower 6.2 that powers Mercedes. Liter M159 engine-Mercedes-Benz SLS AMG Black Series 2013-2014, producing 670 horsepower at 8,400 rpm. Compared with that powerful Mercedes-Benz, how did Chevrolet manage to find a "[745 cubic centimeter] displacement replacement"? Through better breathing and faster engine rotation-after all, horsepower is just torque multiplied by rpm divided by 5,252. Please also note that at 460 lb-ft, this is not the world's most torque V-8 (the Mercedes-Benz above made 468). Here are five ways Chevrolet achieves this goal.
Two huge 87mm throttle bodies provide a separate intake chamber for each cylinder bank of the Z06 engine. It can hold a total of 11 liters of air-twice the displacement of the cylinder. Fun fact: C7 Z06 is fueled by a single 87mm throttle body. In these pressurized chambers, each cylinder inhales through its own unique intake horn, and the angle of the intake horn is slightly different to optimize cylinder inflation. The team is happy to see the aftermarket develop a clear pressurized chamber that allows people to see these speakers, but it is a structural part, and it has not been determined whether the plastic part can be reliably coated with Edge Red to match the cam cover, such as The figure is shown on the display engine.
In the flat crankshaft V-8, the firing sequence is always switched from one row to the other, and there is a lack of the split obtained by the continuous firing of a split cross-plane engine from a single row (this is what caused them to burst). The real intake manifold magic that takes advantage of this potential volumetric efficiency windfall is a series of three valves that connect two intake booster chambers. They open in different combinations to change the pressure wave inside the LT6 engine booster chamber. Or the degree of communication between.
When each of the 32 independent intake valves of the Corvette Z06 is suddenly closed, it generates a pressure wave that is reflected back to the intake runner. When the timing is right, when the intake valve opens to help fill in additional air, the wave will reflect back to the runner. This is called resonance boosting, and it is based on the same Helmholtz resonance effect, which produces a bottle of sound when you blow over the top. This type of supercharging will not cause a loss of horsepower to the engine.
The three intake boost valves are initially closed. Then as the speed increased, one opened at about 2,000 rpm, then all three opened at about 5,800 rpm for a short time, after which they all closed again. (This is the strategy in Sport and Track modes-different strategies are used in Stealth and Tour modes to optimize quiet operation.) This makes the LT6 engine volumetric efficiency rating above 100, which means it can naturally inhale a The volume of air is larger than the static size of its cylinder. This is rare in naturally aspirated road-legal production engines.
One of the main keys to the high-speed characteristics of the LT6 engine—except for the inherently lighter flat crank (without counterweight)—is its super-square cylinder bore and stroke (104.3/80.0mm), which greatly reduces the speed at high speeds. Peak piston speed rotation speed. Short skirts, lightweight forged aluminum pistons, forged titanium connecting rods, and aluminum harmonic balancers all help to minimize the moment of inertia. In the double overhead cam cylinder head, we found that the life-long mechanical valve lifter can eliminate the tilt and friction in the valve train. Each roller follower is supported by one of 40 eyelash caps of different sizes individually selected after high-precision robotic measurement. The resulting tolerances are so strict and precise that they never need to be adjusted. Oh, the titanium alloy intake valve and sodium-charged exhaust valve are closed by double coil springs.
Exhaust is discharged from the LT6 engine through an equal length main pipe, and then flows through a brand new exhaust system. The challenge with a flat crankshaft exhaust system is that the exhaust characteristics are similar to those of two four-cylinder engines. This sounds quite harsh, and connecting the bank through an X tube or crossover tube will often eliminate and attenuate the sound. The Corvette team found that the best result was to place the muffler in the corner of the car and let the pipe exit in the middle. Now, as the loud valve opens, adjacent pipes emit the sound of each cylinder bank, making the exhaust pulses combine in a less noisy way.
The exhaust tip is now mounted on the dashboard and has a parabolic reflector-if you prefer, you can use a reverse loudspeaker whose profile can reflect sound waves forward to the nacelle as they leave the duct radially outward Extension. From this central location, exhaust noise reaches the cabin more directly than from the corner of Stingray.
They sound great. The character is Ferrari-like, but the voice is lower, reflecting Corvette's deeper lungs. As you transition from the track to sports and touring, this role will gradually step down and almost disappear in stealth mode 1. The loud valve is completely closed, and all exhaust gas passes through the entire muffler system and through the smaller external duct (opening in it) Including a perforated outer flange similar to a spark suppressor, but only to match the outer dimensions of the inner pair of pipes). If you are wondering, Stealth Mode 2 will dim all unnecessary cabin and dashboard lighting.
Everyone likes the hiccups and pops when speeding, and Chevrolet delays turning off the direct fuel injectors slightly to encourage this-especially in more aggressive driving modes. But they only do this when your feet are moving. When you back up, you will hear a popping sound, but if you keep the throttle position—even when the car is decelerating—the popping sound will subside.
A brief description of these injectors: Using the lessons learned from Chevrolet IndyCar engines, they are installed on the side of the exhaust valve. This frees up valuable real estate in the valley for a well-designed intake, but it also helps to better mix the fuel. Most engines put them under the intake valve, where they will naturally stay cool, but this usually requires some rollover caused by the intake runner, which reduces volumetric efficiency. The water jacket extends downwards around the fuel injectors, and the exhaust headers are upwards and away from them and are completely wrapped in a heat shield. A large amount of airflow from the side air intakes cools the engine compartment.
The last trick to make a high-strength and complex engine like the LT6 of the 2023 Chevrolet Corvette Z06 is the complex refueling system. Here again, LT6 borrows heavily from racing cars. Each piston pair is sealed to each other so that the air under the piston simply moves back and forth laterally, with minimal pumping loss. The six-compartment oil pump that runs the length of the engine scavenges each compartment plus each cylinder head, requiring 14 horsepower to run. This car requires 10 quarts of 5W50 oil, and through the large oil cooler in the left rear air intake, the daily oil temperature on the track reliably hovers around 250-265 degrees.
An interesting development driver note about this system: pumping 60 psi vacuum. When shutting down, the vacuum draws air through the main crankshaft seal, causing a short whistling sound. A design fix has solved this problem, but one of our development cars has not been updated to the new design.
The Corvette team really hope you like the exhaust sound because it is expensive. When the pandemic closed, spending also stopped. But the computer continues to iterate the exhaust system design, leading to this central exit. Everyone likes this sound, but the cost of tearing up the rear panel design to fit the centrally installed reverse loudspeaker exhaust pipe is "millions." worth!
This does not necessarily help the engine breathe better or spin faster, but it’s worth noting that under the 11-liter intake manifold in the V-shaped valley, most of the engines are suspended on the front or side of the engine. The main components: the starter is installed at the rear of the valley, and the alternator is installed at the front. Two high-pressure fuel pumps are also located here, driven by dedicated cams with lobes optimized for 9,000 rpm operation.
The design team called the LT6 engine series "Gemini" because it uses dual cams, dual throttle bodies, dual high-pressure fuel pumps, and so on. To pay homage to this unofficial nomenclature, you can find small rocket ship icons molded or cast into various engine parts
Since the large naturally aspirated engine is on our extinction watch list, we asked Tadge Juechter, chief engineer of Corvette, about the future of LT6. He assured us that it was developed to meet every projected emission regulation. European regulations are stricter, and the export market requires particulate filters to meet Euro 6d. The biggest challenge to legitimize this racing engine: Let the catalyst ignite at the end of the four-inlet two-in-one header, its size can optimize scavenging (resonant supercharged suction and exhaust counterpart). But the catalyst light-off fuel strategy seems to have worked.
Photos taken by William Walker, Jason Lanham/Astro Creative and the manufacturer
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