GM Announces 5.5L LT6; 670HP, Four Cams, And A Flat-Plane Crank

We’ve all heard the rumors of a dual overhead camshaft V8 engine for the Corvette. Some lost hope when the 2020 Corvette debuted with the LT2 variant of the Gen-V direct-injected small-block Chevrolet. Some speculated that the Cadillac Blackwing’s 4.2-liter DOHC engine would be the basis for the upcoming Z06’s new architecture. Those hopes seemed to be dashed when Cadillac dropped the DOHC powerplant for an LT4 based option.

Not all hope was lost, however, as Chevrolet teased that the 2022 Z06 would feature a flat-plane crankshaft. That feature alone didn’t confirm or kill a dual overhead camshaft arrangement, but sparked interest nonetheless. However, at today’s Corvette Z06 reveal, we got our first look at the car’s new powerplant — The LT6 — and it has four cams.

Here you can see some of the details of the all-new LT6 engine. Chain-driven dual overhead camshafts, active intake manifold butterflies, and an exhaust with an incredible amount of engineering in it are just a few of the incredible features of this new engine. Photos by Dave Cruikshank

5.5-Liter LT6

While all of the details and specs aren’t yet available, what we do know is pretty amazing. The engine is rated at 5.5 liters of displacement — or 333 cubic inches — thanks to the 104.25mm (4.104 inches) bore diameter and 80mm (3.150 inches) stroke. The clean-sheet block design retains the standard 4.400-inch bore spacing, meaning the bore, as delivered, is close to, if not the absolute limit.

The engine will feature forged-aluminum pistons connected to forged-titanium rods — a combination we’ve seen from GM before in the LS7 — but what is all-new for GM is the 3.15-inch stroke flat-plane crankshaft. “With a flat-plane crankshaft, the mass that is moving the fastest, is much lighter. That allows the engine to accelerate much more rapidly than any small-block before it,” says Dustin Gardner, Assistant Chief Engineer, LT6

Another all-new feature (for an LT-platform engine, at least) is the dual overhead camshaft cylinder heads. The four camshafts are chain-driven and use a mechanical finger-follower setup to translate cam motion into valve motion, with dual valvesprings controlling the whole affair. The four-valve-per-cylinder design features 32 valves (16 titanium intake valves and 16 sodium-filled exhaust valves, similar in construction to the LS7’s), and incredible efficiency, with our good friend Billy Godbold of Comp Cams running the numbers and noting an estimated 95- to 98-percent volumetric efficiency at peak horsepower.

Looking into the intake manifolds, the level of effort to achieve that efficiency is obvious. Each bank has its own plenum and throttle body,  with each cylinder’s intake runner having its own bellmouth to smooth airflow into the cylinder, as well as an active intake airflow management system (no, not DOD or AFM). Direct injection is almost a given in today’s world, and the ignition system appears to be a fairly traditional coil-on-plug system mounted to the valve covers.

How Much Power Does The LT6 Make?

With SAE power certification testing just recently completed, the engine is rated at 670 horsepower at an amazing 8,400 rpm with 460 lb-ft of torque at 6,300 rpm. The maximum RPM limit in the production vehicle will be 8,600 rpm, which while impressive, isn’t surprising, given how oversquare the engine is. “It makes power all the way up, so even in the upper RPM range you can still feel it pulling,” explains Cindy Molnar, Vehicle Performance Engineer, Chevrolet Performance Cars

The LT6 makes peak power at 8,400 rpm and is rev-limited to 8,600 rpm. The highest engine speeds of any factory Corvette ever.

“An Engine of this nature is truly playing in the exotic space, Gardner explains. “It is a low-volume, hand-built, precision engine. The manufacturing tolerances in this engine are racecar tight.” What that all amounts to is the most powerful naturally aspirated V8 engine to ever grace a production vehicle. A crown the team at Chevrolet hopes to wear for a considerable amount of time.

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About the author

Greg Acosta

Greg has spent seventeen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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