Chevrolet Gemini small-block engine

The Chevrolet Gemini small-block engine is a dual-overhead cam (DOHC) V8 engine designed by General Motors. While technically a small-block engine because of its bore spacing of 4.4 inches, General Motors engineers do not consider it to be a part of the traditional Chevrolet small block lineage because of the substantial reworking, specialized development, and unique technical features distinguishing its design.

The LT6 is a clean-sheet design, mechanically unrelated to both the LS-based engines and the Cadillac Blackwing V8. Its most notable traits include a flat-plane crankshaft and dual-overhead camshafts, which represents a departure from the traditional pushrod valves and crossplane crankshafts found in all previous generations of Chevrolet small-block engines. As of May 2024, the Gemini engine has only one variant, dubbed LT6. Hagerty, an American insurance company, reported in 2020 that a higher horsepower variant, the LT7, is expected to arrive in the 2024 model year.

LT6
The LT6 is a 5.5-liter, naturally-aspirated V8 engine. It debuted in the eighth-generation Corvette Z06, and was unveiled on October 26, 2021.

While the LT6 features a redline of 8,600 RPM, it generates a maximum of 670 hp at 8,400 rpm and 460 lbft of torque at 6,300 RPM. These figures make it the most powerful naturally-aspirated production V8 engine of all time; the engine to previously hold this title, the Mercedes-Benz SLS AMG Black Series M159 6.2-liter V8, made 622 hp at 7,400 RPM.

The LT6 is also the largest flat-plane V8 used in a production car by displacement, dethroning the Ford Voodoo. This is notable due to the additional vibrations inherent to this architecture compared to a crossplane V8, which tend to scale up with displacement.

A modified version of the LT6 has powered the Chevrolet Corvette C8.R since 2019, and many features in the racing engine carry over to the road engine. Other notable features include a cast aluminum block, dual coil valve springs supporting titanium intake & sodium filled exhaust valves, forged aluminum pistons, forged titanium connecting rods, active split intake manifold with twin 87mm throttle bodies, four-into-two-into-one stainless steel exhaust headers, and a factory six-stage 10-quart dry sump oiling system with individual crank bay scavenging.

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