LT6 Engine Ultimate Guide
Tuesday, October 26, 2021, was a big day in the world of the Chevy Corvette. We, along with the rest of the world, got our first real look at the all-new 2023 Corvette Z06. Since its introduction, the internet has been abuzz with all sorts of news about Chevrolet’s newest super car. From its track-bred architecture to its near hyper-car performance potential, there’s been a lot of conversation about what drives this beastly Corvette. It is with this thought in mind that we decided to proverbially “look under the hood” and share all we could uncover about GM’s all-new LT6 5.5-liter engine.
Let’s start with some statistics. First, this latest engine is the most powerful naturally aspirated, internal combustion engine (by a good margin) of any production Chevrolet small-block ever produced. Boasting a massive 670 horsepower, the LT6 trumps almost all its Corvette predecessors (save for the 2019 Corvette ZR1’s Gen V LT5 engine, which boasted 755 horsepower, but only with the aid of an Eaton supercharger – the LT6 has none.) It also outpaces the C7 Z06’s LT4 engine by twenty horsepower.
DOHC, VALVES & LIFTERS
The LT6 utilizes a DOHC (That’s a “Dual Over Head Camshaft” for the uninitiated) configuration. The DOHC setup was lifted directly from Corvette Racing’s C8.R setup. The same is true for many of its other components as well. Virtually identical cylinder heads, valves, ports, combustion chambers….and everything is CNC machined, another indicator of the precision powerplant engineering usually found on engines used in a race car.
The car requires larger intake and exhaust valves to properly feed and vent the engine’s massive 4.104-inch cylinders. The intake valves’ have a diameter of 1.654 inches (42mm) while the exhaust valves measure 1.378 inches (35mm). A generous 58.8cc combustion chambers allows the engine to operate at a 12.5:1 compression ratio. As with all Corvettes past and present, the 2023 Z06 will require premium (or better) fuel.
The LT6 utilizes hollow camshafts and variable valve timing. They are phased by an electro-hydraulic system that allows for approximately 55 degrees of authority on the intake came and approximately 25 degrees on the exhaust, both of which should allow the engine to be more drivable in its lower rev ranges.
The cams depress finger followers. In turn, the followers actuate the titanium intake valves and sodium-filled exhaust valves. The valves are controlled at high rpm by twin valve springs, with a smaller spring cradled inside a larger, outer spring.
The LT6 utilizes solid lifters, with the lifter being the intermediate part between the cam follower and the intake and exhaust valves. In the past, lifters of this type would typically require adjustment over time. However, Chevy claims that owners won’t have to adjust the lifters on the LT6 because of the precise fit between the finger follower and the lifter itself. Additionally, an oil jet has been positioned to spray oil through the finger follower and onto the area where the cam surface and the follower come into contact.
DRY SUMP OIL SYSTEM
The LT6 engine will utilize a dry sump oil system, and is engineered to operate using a full synthetic 5W50 oil weight, which is pumped thru the engine very quickly. As much as 80 percent of the engine’s oil will remain in the sump, and the sump system will circulate enough oil to fully lubricate the engine without having excess oil slow down fast moving components like the crankshaft. There are four points in the crankcase and two points in the heads thru which oil returns to the remote sump.
A vital aspect of the engine’s oil system is its bolt-on, cartridge-style oil filtration system. This type of filter was selected out of necessity based on the types of vibrations created by a flat plane crankshaft. Per GM’s engine program engineers, they observed the early spin-on oil filters literally vibrating off the engine during a high RPM dyno testing. The bolt-on filter became the logical answer.
FLAT PLANE CRANKSHAFT
The LT6 engine utilizes a forged steel, flat plane crankshaft which is bolted to the block via four bolts per main cap. This crankshaft creates a rather short 3.150-inch (80mm) stroke, which is typical in higher-revving engines. The LT6 has a bore/stroke ratios of 1.3:1. Per an article published in “Engineering Explained,” the higher the bore/stroke ratio is, the higher the theoretical “revability” is. Consider this, the current Porsche GT3 has a bore/stroke ratio of 1.25:1, and the base C8 Mid-Engine Corvette a ratio of just 1.12:1. At the other end of the spectrum, a current F1 engine’s bore/stroke ratio is 1.51:1.
Of course, the high efficiency and revability of the engine requires fortified bottom-end hardware, which the LT6 provides in the form of forged titanium connecting rods, pistons, and (as mentioned earlier) the crankshaft itself.
ALL NEW EXHAUST NOTES
While we appreciate the incredible efficiency of the engine itself, it is equally important to look at how the engine exhausts its spent energy (and fuel). As with the LT6 engine, GM’s engineers have invested considerable time into the creation of an exhaust system that will provide increased exhaust flow and will utilize “exhaust scavenging.” Exhaust scavenging is a process by which an “exhaust pulse” travelling down the exhaust pipes draws other pulses down the tube with it, thereby increasing exhaust flow.
The exhaust system utilizes a 4-2-1 setup, with four exhaust pipes combining into two pipes, then the two pipes combining into one. What’s interesting is that while it appears there are quad tips emerging from the rear of the car, these “tips” are actually just finished behind a unique bezel that was designed to function like a “reverse trumpet.” Chevrolet engineers designed these reverse trumpets to reflect the engine’s high-pitched exhaust note back towards the car’s cockpit, giving the car’s occupants an unprecedented connection to the exhaust sounds normally only observed by other drivers trailing the car.
This is an engine (and a Z06 Corvette) built from the heritage of the Corvette Racing program. More than that, it was built in conjunction with the latest racer, and we suspect that the new 2023 Corvette Z06 will share a kindred relationship with the C8.R in a way that no other Corvette before it has…and that’s saying something given that the mid-engine C8 Corvette represents the third-generation of Corvette built alongside its track-born counterpart.
We expect great things from the 2023 Corvette Z06…and I’m confident we won’t be disappointed.
|Type:||LT6 5.5L DOHC V-8 Direct Injection|
|Bore & Stroke (in / mm):||4.104 x 3.150 / 104.25 x 80|
|Block Material:||A319-T7 sand-cast aluminum with pressed-in iron cylinder liners and four-bolt main bearing caps|
|Oiling System:||Six stage dry sump (8-qt. capacity); includes oil-spray piston cooling|
|Oil Type:||DexosR synthetic 5W50|
|Cylinder Head Material:||A356 T6 cast aluminum|
|Combustion Chamber Volume:||58.8cc|
|Valvetrain:||Dual overhead camshafts with mechanical finger follower valvetrain and dual-coil valve springs|
|Valve Size (in / mm):||1.654 / 42 titanium (intake) & 1.378 / 35 sodium filled (exhaust)|
|Fuel Delivery:||Exhaust side direct injection. Max pressure: 5,076 psi (35 Mpa / 350 bar)|
|Throttle Body:||Twin 87mm single bore (electronic)|
|ECU:||GM E68 (32-bit processing)|
|Horsepower (hp):||670 @ 8400 rpm (GM tested per SAE J1349)|
|Torque (lb-ft/ Nm):||460 / 623 @ 6300 rpm (GM tested per SAE J1349)|
Many tried and true design segments in this engine. The best feature is the use of a single plain crank, which definitely effects crank harmonics and torsional forces. I also like the use of the finger approach to the cams, especially the shortness of them. Definitely like the hollow cam approach. I played with a DOHC design for a small block back in the 60’s and utilized that idea too. All in all, a brilliant engine.
Will the LT-6 engine & transmission combination be available for purchase from the GM High Performance catalog?