WHILE we love the LS and LT-series Gen III-V small block engines for their compact size and low weight, the writing has been on the wall for them since images were leaked showing General Motors was developing new overhead-cam V8s. Today, we got our first look at the details behind one of these engines, a twin-turbo 4.2-litre unit that has two cams sitting in each of its cylinder heads.

Cadillac has used overhead-cam V8s before, most notably the Northstar family, but this is a whole new, “clean-sheet” design they’ve spent three years developing, and it is intended for the top-dog CT6 V-Sport. They have announced two variants, with one making 550hp and 850Nm, and a de-tuned version spitting 500hp and 750Nm.

Using the conventional 90-degree bore angle, the new motor is all-aluminium, runs six-bolt mains, and has 96mm bore spacing with press-in iron cylinder liners. It is reported the engine has a forged steel crank and rods, with aluminium pistons, with 86mm bores to minimise piston weight (improving the engine’s keenness for RPM). Compression ratio will be 9.8:1, while there will be twin throttle bodies and a new E68 ECU.

The 4.2 uses a “hot V” design where the twin-scroll turbochargers and cat convertors sit above the valley, between the head castings. This is to reduce lag and packaging issues, although leaked CAD images from General Motors shows they have also been developing another twin-turbo quad-cam V8 where the turbochargers are positioned in more conventional fashion, down beside the block.

For the Cadillac 4.2 V8 the intake manifold will be an integrated unit sitting outboard of the cylinder head, where the exhaust manifold sits on a conventional V8. These new motors will feature direct injection and Active Fuel Management, while GM have confirmed a next-gen cylinder deactivation is also on its way soon. The Cadillac four-cam donks will mate to a 10-speed electronically controlled 10L90 Hydra-Matic automatic, which is apparently all-wheel-drive only!

Interestingly, these new engines will be built at GM’s Bowling Green Performance Build Centre in Kentucky, right near the Corvette plant. This is of note as leaked CAD images have shown a twin-turbo 5.5-litre quad-cam V8 engine with up to 850hp, in a mid-engined format (which is widely rumoured how the next-generation Corvette will be built).

While they will likely need pushrod motors for at least five years for their pick-up truck programme, this may signal the writing is on the wall for the traditional Chevy pushrod V8.