LT7: How GM Made the Twin-Turbo, Flat-Plane 5.5L V8 Stronger Than the N/A LT6

GM didn’t just slap a couple of turbos on the LT6 and call it a day. We look at everything that was done to create the 1,064 HP LT7.

The 2025 C8 ZR1 has finally been revealed. The car is a staggering piece of machinery. And at center stage is the 5.5L LT7 twin-turbocharged DOHC V8. (And, yes, it’s still got a flat-plane crank.) This incredible engine makes 1,064 horsepower and 828 pound-feet of torque. It is based on the LT6 that is found in the engine bay of the C8 Z06. But GM didn’t just bolt on some turbos and walk away. The C8 ZR1 needed to make big power. But headline-grabbing power is one thing. Engineers have to make sure that the engine is as reliable as it is powerful (because warranty). That means several parts of the engine, and the attached transmission, needed to be enhanced to support the added temperatures and forces involved with making more power.

As you may remember, the LT6 program was dubbed “Small Block Gemini” and there are several Gemini easter eggs that can be found on the LT6. But this Gemini engine program was not just for the development of the naturally aspirated LT6. The other goal of the program was to create a turbocharged version using the same architecture. This is the first turbocharged factory Corvette in the 70+ year history of the model. Let’s take a closer look at what exactly went into creating this boosted LT7 engine that is about to take the automotive world by storm.

Unique LT7 Features

The LT7 has many features that separate it from its normally aspirated LT6 sibling. Below is a list of these features (courtesy of Chevrolet):

• Head castings with unique ports and a larger combustion chamber
•  Valve train timing and lift profile optimized for forced induction with higher exhaust temp enabling exhaust valves
• Completely new intake system tuned for twin turbochargers
• CNC machined combustion chamber, exhaust, and intake ports specific to the LT7
• Dual, ported shroud, ball bearing, mono-scroll (76 mm) turbochargers integrated with the exhaust manifold to reduce the volume and distance from the exhaust valve to the turbine wheel for quick response with electronic wastegates
• Intelligent anti-lag engine calibration techniques specifically for ZR1 that adapt and react to driving style
• Added block and head machining to support turbo cooling and oiling
• Counterweight changes to account for a unique piston, and unique connecting rod for the crank train
• A secondary port fuel injection system added to deliver the needed additional fuel to support the engine’s massive output

LT7 Assembly

The LT7 will be hand-built by master engine builders at the Performance Build Center, part of the Bowling Green Assembly Plant in Kentucky. It even includes a unique Edge Blue engine cover. There is no word whether ZR1 buyers will have the option to partake in the Build Your Own Engine program. But no matter who builds it, the LT7 is designed to retain the loves to rev character that the LT6 also enjoys. Peak power is made at 7,000 rpm and peak torque comes on at 6,000 rpm.

Transmission Upgrades

The transmission found in the C8 Z06 is fantastic. However, it needed to be beefed up in order to survive a nearly 60 percent increase in power. To support the four-figure power output engineers made several changes to the Corvette ZR1’s eight-speed dual-clutch transmission, including:

•  Inner and outer input shaft upgrades
•  Increased gear capacity with strength increased via shot peening for all gears
•  Final drive refinements
•  Oil management to support increased vehicle longitudinal and lateral capability
•  Increased control valves to accommodate the higher required clutch clamp load for LT7

A lot went into creating the most powerful and fastest production Corvette the world has ever seen. The specifications are impressive. And now the wait to drive it is even more difficult.

Images: Chevrolet 

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