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THE 5.5L LT6 V8 IN THE C8 CORVETTE Z06 WAS CODENAMED ‘GEMINI’ AND OTHER NEW DETAILS

The LT6 Is A Truly Remarkable Engine, And The Devil Is In The Details

LT6 5.5L DOHC Flat Plane Crank V8 2023 C8 Corvette Z06
LT6 V8 Engine. Image via GM.

As much as has already been said about the remarkable 5.5L LT6 flat-plane-crank V8 that powers the new 2023 Chevrolet Corvette Z06, there will always be plenty more to say. If the engine is the heart and soul of a sportscar, the C8 Z06 has vastly more charisma than most, with 670 horsepower and an eardrum-shattering 8,600-rpm redline.

It’s a heart and soul worth talking about.

Hagerty‘s official Corvette-nerd-in-residence, Don Sherman, just penned an incredibly detailed deep-dive into the Corvette Z06’s very special LT6 V8 – an engine that GM chose to give the codename “Gemini”. It essentially revealed everything a red-blooded performance enthusiast could ever want to know about the most powerful naturally aspirated V8 ever dropped into a production car.

It Took Eight Years To Develop

The LT6’s “Gemini” codename was used throughout a development cycle that spanned eight years. If you’ll notice, that would place the start of development some time around 2015 or 2016 – shortly after Ford dropped its rear-mid-engine, 647-horsepower GT bombshell on the 2015 Detroit Auto Show, before promptly snatching a class win at the 2016 24 Hours of Le Mans.

A quick look around the engine tells you everything you need to know about how its genesis took up the better part of a decade. While the Chevrolet Corvette Z06 mill shares its 4.4-inch cylinder-bore spacing with myriad different small-blocks of yesteryear, that’s about all it shares; predictably, it’s quite oversquare, with a big 104.25-mm bore paired with one of the shortest strokes GM has ever used on a production motor: 80 mm. That, of course, lends itself to the LT6’s rev-happy nature and sky-high redline – virtues further aided by the forged steel flat-plane crankshaft and dual overhead camshafts.

LT6 V8 Engine
Image via GM.

Flat-plane cranks are generally lighter and easier to manufacture than their cross-plane counterparts, and they allow for evenly-spaced intake and exhaust pulses that help smooth out flow and maximize exhaust scavenging. Unfortunately, they also tend to bring extra vibration into the picture, so GM had to specially tune the Corvette Z06 engine mounts to alleviate the extra shake as much as possible. They also developed a heavy-duty aluminum canister for the oil filter to keep the filter from spinning itself off during spirited driving, and affixed the oil reservoir with vibration-damping rubber isolators.

An Engine For The Space Age

The forged steel crankshaft is a necessity for the kind of speeds that the Gemini spins up to, but GM also felt it prudent to source forged titanium connecting rods from Austria and super-short-skirt forged aluminum pistons from trusted racing parts supplier CP Carrillo. Both the cylinder case and oil sump are made from heat-treated A319 aluminum alloy, with a special talcum additive to smooth out spots that are in contact with coolant and oil, presumably for less-turbulent flow. Meanwhile, the cylinder heads are heat-treated A356 aluminum alloy, with fully CNC-machined combustion chambers and intake and exhaust ports.

Image via GM.

But arguably the pièce de résistance is the sophisticated glass-reinforced nylon intake plenum. That’s something we’ve written about in-depth before, but the short version is this: a clever chambered design and a set of electric servo-controlled valves allow the intake to make use of Helmholtz Resonance at a range of operating speeds to cram more intake air into each cylinder. In essence, it lends a slight supercharging effect, without the need for a supercharger.

And what about that codename, Gemini? The name is a bit of an homage to NASA’s second human spaceflight program, and as we all know, the Chevrolet Corvette has a long history with America’s astronauts. But “Gemini” also means “twins” in Latin, which Don Sherman points out makes it a fitting name for an engine that, unlike the vast majority of GM V8s before it, has dual camshafts per cylinder.

As a nod to the engine’s codename, GM has placed a total of 54 small rocket insignias around the Chevrolet Corvette Z06 engine, although most of us will never be so lucky as to see even one of them in the flesh.

Written by Aaron Brzozowski

Aaron has held multiple positions in the automotive industry, from magazine videographer to dealership sales. And because his background isn't diverse enough, he's currently attending engineering school at University of Michigan Despite his expertise in covering the American performance vehicle industry, he's a devout Porsche enthusiast.

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