For over a decade, Mother Mopar has owned the late-model V8 horsepower war with its Hellcat and Demon blown Hemis, but Chevrolet has just laid a king-hit on Team Dodge with the release of its C8 Corvette ZR1. That’s because the new LT7 V8 that powers the 2025 ’Vette is the most powerful production engine ever produced in America.

First published in the Sepember 2024 issue of Street Machine

Boasting 1064hp at 7000rpm and 828lb-ft of torque at 6000rpm, the 5.5-litre, DOHC LT7 is boosted by two turbos, making the C8 ZR1 the first-ever factory-turbocharged Corvette. To put the new donk’s performance into perspective, it not only produces more power than the 2023 Dodge Demon 170, but also bests hypercars like the Ferrari LaFerrari, Porsche 918, Mercedes-AMG ONE and McLaren Speedtail!

While it shares the familiar Chevy small-block (and LS and LT) bore spacing of 4.4 inches, the LT7 is a galaxy away from the GM pushrod engines we’re used to. As part of General Motors’ Gemini engine program, the LT7 is closely related to the C8 Corvette Z06’s 670hp LT6, which is the world’s most powerful aspo V8. Both engines share an alloy block design, though the LT7 has extra machining to support turbo cooling and oiling.

The LT7 also runs the same style of flat-plane crank as the LT6, with GM engineers believing the high-rpm capabilities of a flat-plane give a much better performance driving experience than an engine using a cross-plane crank (see more, below). The LT6 and LT7 share the same 104.25mm bore and short 80mm stroke, but changes were made to the LT7’s crank counterweights to account for the unique dished pistons and shorter conrods used.

GM also dropped the compression on the LT7 from 12.5:1 to a boost-friendly 9.8:1, and the redline was pulled back to 8000rpm from the LT6’s 8400rpm. The dry sump oiling system from the LT6 has been carried over to the new engine, but it now has seven scavenging stages, as the low-mount turbos needed a scavenge port to ensure a constant oil supply.

To supply the go-sauce, the LT7 relies on both port and direct injection (DI), similar to the system found on the C7 ZR1’s blown LT5. Because DI systems aren’t easily upgraded to handle the kind of power the LT7 puts out, the simplest solution was to plug eight extra port injectors into the intake manifold. The LT7 idles on the port injectors, brings the DI system on board while driving, and then uses all 16 injectors when going flat-out.

GM engineers drew up new cylinder heads for the LT7, featuring CNC-machined 59cc combustion chambers and a fresh port design, and the valvetrain (including camshafts) was also redesigned with boost in mind. The new heads feature 45mm titanium intake valves and 35mm exhaust valves made from a high-nickel superalloy called Nimonic, chosen for its ability to withstand the extreme temperatures the exhaust side of the motor will see. The LT6’s radical intake manifold was binned in favour of a more traditional plenum with twin 65mm drive-by-wire throttles, as the boosted LT7 didn’t need the airflow trickery of the highly strung aspo mill.

The LT7’s twin 76mm BorgWarner ball-bearing turbos feature electronically operated wastegates, and are mounted on integrated exhaust manifolds. The big snails feature port shrouding, which has been used on aftermarket turbos for years to improve boost response and stability. There’s also “intelligent anti-lag” on the ECU tune, which GM claims will adapt to a driver’s style. The turbos push 20psi worth of atmosphere into the spicy V8, but can go up to 24psi when heat loads rise, countering the effects of poor air density. Intake charge is cooled by a pair of water-to-air intercoolers mounted on top of the engine.

Initially, Gemini engineers only wanted the LT7 to make 800hp, but the very first dyno runs bested that figure even with the wastegates held wide open to give the lowest possible boost. While all LT7s will be hand-assembled at GM’s Performance Build Centre in Bowling Green, Kentucky, the 1064hp small-block has passed GM’s 240,000km street-driven durability testing, and carries a warranty.

There is no word yet on whether the LT7 will end up as part of Chevrolet Performance’s range of crate engines, but previous ZR1 powerplants like the C6 LS9 and C7 LT5 have both been available aftermarket. The good news is that the LT6 and LT7 share their bellhousing pattern with the garden-variety pushrod LTs, making it easy to fit a transmission suited to front-engine layouts.

We can’t wait to see if the LT7 pop ups on Chevrolet’s stand at SEMA 2025 with a part number and price tag. BLOBAK 3, anyone?

Flat-plane crank: why is it so?

The GM brass have repeatedly claimed that the decision to equip the LT6 and LT7 with a flat-plane crankshaft was simply to allow for high-rpm fun. Certainly, a flat-plane crank is great for a performance car because it removes the need for counterweights and fires the cylinders in sequence on opposing banks. With a large bore and short stroke, this adds up to a high-rpm screamer of an engine, which is exactly what you want on a twisty road or race track. But we suspect there was a bit more to GM’s decision than just that.

In moving the Corvette to a mid-engine platform, Chevrolet head honchos claimed it was because they’d done all they could with a front-engine layout. What wasn’t said was that the company wanted to up the price tag for Corvettes to help recoup ever-increasing development costs, thus pushing the car into genuine supercar territory.

Moving to the mid-engine platform meant Chevrolet could then explore proper sports-car traits like a high-rpm, overhead-cam, turbocharged drivetrain package, which wouldn’t have been as attractive to traditional Corvette buyers when the car had its pushrod V8 mounted between the front wheels.

Put simply, the Chevrolet bigwigs know they need a slice of the European supercar market to keep the Corvette alive and profitable, and the flat-plane set-up lends the ’Vette an aura of credibility in that space, as manufacturers like Ferrari have used flat-plane V8s for decades.

GENERAL MOTORS LT7