GM plotting biturbo DOHC V8

The death of Holden's homegrown Commodore in 2017 might also spell the end of Chevrolet's small-block pushrod V8 in Australia, but General Motors is working on an all-new twin-turbo DOHC V8 that could eventually become available here.

Hopes of a born-again DOHC from GM were sparked in 2013, when Cadillac revealed the Elmiraj luxury coupe concept powered by a 373kW/678Nm 4.5-litre twin-turbo V8.

Then early last year new Cadillac president Johan de Nysschen told US publication Car and Driver that the brand's new CT6 limousine; would be available with "a high-performance advanced V8 turbo" to go with its 2.0-litre four-cylinder and (300kW) 3.0-litre V6 turbo engines.

Now, de Nysschen has told the same Detroit-based website the all-new GM V8, which will debut in the CT6, will displace 4.2 litres, incorporate two turbochargers and deliver a horsepower output in the "upper 400s" [500hp = 373kW].

This is significant for a number of reasons, beyond confirming Cadillac will finally have a modern downsized twin-turbo V8 to compete with 4.0-litre biturbo eights from German luxury car rivals like Audi and Mercedes-AMG.

The move indicates GM has revived its still-born DOHC V8 program, which was shelved with the GFC in January 2008. Codenamed 'Ultra', the next-generation V8 was to have replaced the decades-old 4.6-litre Northstar DOHC V8, which was later discontinued in 2010.

At the time, the engine was expected to share technologies with GM's Melbourne-made High Feature V6, including continuously variable valve timing for both intake and exhaust, and was to be built for both longitudinal (rear-drive) and transverse (front-drive) applications at the company's Tonawanda plant in the US.

In 2007, before the program was axed, one GM powertrain executive told US website Inside Line the engine was "as refined as anything in the history of internal-combustion engines. It was the quietest engine we've ever tested."

The new V8 marks the combination of both biturbo and DOHC technologies for the first time for GM. While the Northstar V8, which was introduced by Cadillac in 1993, featured double overhead cams and even supercharging, it was never turbocharged.

The last time a twin-turbo GM V8 appeared in dealerships was in the C4 Corvette, which was available with a Callaway-tuned L98 V8. But like all small-block Chevy V8s remain to this day, it was a pushrod engine with a single crankcase-mounted camshaft.

The latest and greatest iteration of GM's small-block pushrod V8 is the 6.2-litre Gen 5 LT1, which debuted in the 2014 C7 Corvette Z06 with 466kW and 861Nm, while a naturally aspirated 339kW version powers the new 2016 Camaro SS.

Both LT1 engines will eventually supersede the 6.2-litre Gen 4 LS3 V8 that powers Holden's existing Commodore, but both models remain left-hand drive and have been ruled out for Australia.

GM's new biturbo DOHC V8, meantime, will debut in the Cadillac CT6 and is also expected to power a future Cadillac limousine to rival the BMW 7 Series and a future sports car to rival the Porsche 911, but Cadillac has been ruled out for RHD markets including Australia until next decade.

However, the new downsized 4.2-litre V8 could also find its way into the next-generation C8 Corvette, which is under development and will reportedly be mid-engined. It could also be matched with GM's first dual-clutch automatic transmission.

If the next Corvette does indeed turn out to be the mystery V8 sports car promised by Holden, it could arrive here with the most advanced GM V8 ever produced.