How Chevrolet Made the C8 Corvette Z06 Engine Bomb-Proof

The C7 Z06 had major overheating problems. The team behind the new LT6 V-8 worked hard to vanquish these issues.

c8 corvette z06 lt6
Chevrolet/Illustration by R&T

Recently, GM hosted an event where engineers from the Chevrolet Corvette and Small Block programs gave a three-plus-hour presentation on the LT6, the engine powering the new C8 Corvette Z06. The most common point of reference throughout was the LT4, the supercharged 6.2-liter V-8 used in the C7 Corvette Z06, and currently found in the Camaro ZL1 and Cadillac CT5-V Blackwing. It's a killer engine, though early on, it was plagued with faults.

Namely, overheating. In track use, early C7 Z06s had a habit of hitting high engine temperatures and going into limp-home mode, something that led owners to file multiple class-action lawsuits against GM. Chevy fixed the problem by raising the supercharger cover starting with the 2017 Z06, but the damage to GM's reputation for building durable track cars was done. It was a rare miss for team Corvette, and while no one directly mentioned the LT4's issues in the LT6 presentation, the subtext was, "we know where we screwed up with the LT4-powered C7."

(We should note that the LT4 hasn’t shown heat-soak issues in the Camaro ZL1, the 3rd-generation Cadillac CTS-V, or the current CT5-V Blackwing. Cadillac's media launch for the CT5-V Blackwing was held at Virginia International Raceway last summer, and the cars presented no issues lapping all day in 95-degree heat with A/C on.)

LT6 engineers spent lots of time talking about how they achieved such impressive figures with this all-new 5.5-liter V-8: 670 hp at 8400 rpm, 460 lb-ft of torque at 6300 rpm, and an 8600-rpm redline. But they dedicated just as much time to explaining the cooling system, and how the engine was made to be robust.

c8 corvette lt6 block castings
LT6 block castings.
Chevrolet

That starts with how the LT6 is constructed. The block is made of two separate aluminum castings: one for the cylinders, water jackets, and the upper half of the crankcase, the other forming the lower crankcase and holding the oil scavenging system. It's a highly unusual design—the vast majority of V-8s built since the Thirties use a single casting for block and crankcase.

lt6 gunslit
The LT6 "gun-slit."
Chevrolet

This design was employed to maximize the efficiency of the dry-sump lubrication system. Casting the crankcase separately allowed Chevy to create four sealed crankcase bays, which help to keep air out of the system, allowing the crankshaft to spin more freely and reducing pumping losses. Each crank bay has what engineers call a "gun slit" to allow oil into an individual scavenge circuit. "It's critical in a high performance engine to not aerate the oil and get it out of the crankshaft," says Jordan Lee, chief engineer for GM Small Blocks. Aerated oil wreaks havoc on bearings, and the new crankcase design and dry-sump system are designed to keep oil air-free.

lt6 oil tank
LT6 oil tank.
Chevrolet
2022 lt6 oil pump
LT6 oil pump. Note the six scavenge circuits in at the bottom left. 
Chevrolet

There are six oil scavenge circuits in total: one for each crank bay, one that gets oil from the front cover, and one for the cylinder heads. The oil tank itself sits right on top of the pump at the front of the engine. Engineers are particularly proud of the system's efficiency, noting that at 8600 RPM, 96 percent of the engine's oil—eight quarts of 5W50—remains in the tank. That outperforms the LT4, which only retained 68 percent of its oil in the tank at redline. There's also a bottom-mounted oil cooler, which engineers say has 85 percent more cooling capacity than the LT4's. Lee says the goal with the LT6 was to keep oil temperature below 248 degrees F on track, and in track testing, temps rarely exceeds 230. The system can handle 1.25g of lateral or longitudinal acceleration, so oil starvation shouldn't be an issue.

lt6 radiators
Chevrolet

Of course, the oiling system is critical in making a durable engine, but it doesn't stop there. Compared with the C8 Stingray, the Z06 has two additional radiators, one in the center of the front grille, and one at the driver's side rear for oil cooling. The two outboard front radiators each get a new fan and a new compressor. For track driving, the front license plate bracket is easily removed, increasing cooling airflow to the center radiator. The LT6 even gets a larger A/C compressor and pulley compared to the LT2 in the Stingray, for those 100-degree track days.

2023 corvette z06 lt6
LT6 cranktrain.
Chevrolet

Chevy went fancy with the engine materials, for both strength and lightweighting. The forged titanium rods are the lightest ever in a Z06, as are the forged aluminum pistons. The pistons and mechanical finger followers get a diamond-like carbon coating to reduce friction. With no hydraulic tappets, the finger-follower valvetrain has “set for life” lash and gap, and after 100,000-mile tests, engineers saw "negligible" wear on these components. They also claimed to see no unusual oil consumption in track testing, and said the vacuum created by the new crankcase design actually helps keep the piston rings seated.

2023 corvette z06 lt6
LT6 valvetrain.
Chevrolet

The LT6 is a radical departure from GM small-block tradition, incorporating engineering solutions commonly associated with limited-production cars without demanding the special treatment of those machines. "You get the exotic engine, but not the exotic ownership experience with extraordinary maintenance bills and frequency of maintenance," says Corvette chief engineer Tadge Juchter. "There is no special maintenance," Jordan Lee adds. "Change your oil and your filter, and change your spark plugs after 100,000 miles."

It's clear that the Corvette and Small Block teams want to win back those disappointed by the problems with the last Z06. The Z06 is supposed to be the most track-focused Corvette, and those early LT4 issues really damaged the C7 version’s reputation. With the C8 Z06 and its LT6, GM engineers are looking to right those wrongs. It's an enticing promise: The most powerful naturally aspirated road-car V-8 ever, with the reliability and durability we’ve come to expect from a small block.

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