In the latest signal that automakers aren’t shutting off investment in internal-combustion just yet, General Motors’ Cadillac premium-vehicle brand unwrapped an all-new V8 roughly four years in the making. Cadillac will begin with exclusive use of the twin-turbocharged 4.2-L DOHC V8 starting in the first half of 2019 with a high-performance V-Sport variant of the CT6 flagship sedan—but it’s easy to speculate the V8 could be earmarked for future use by at least one other important GM model.
Revealing the new V8 architecture to a small media group, Jordan Lee, chief engineer for Cadillac V8 engines, said the engine is intended to underscore the Cadillac brand’s exclusivity and performance heritage and deliver an appropriate blend of high performance and refinement. The updated 2019 CT6 lineup will offer two variants of the new V8: a high-output version for the V-Sport model that generates an estimated 550 hp at 5,700 rpm and peak torque of 627 lb·ft (850 N·m) from 3,200-4,000 rpm.
The standard variant of the all-aluminum V8 is projected to produce 500 hp at 5,000-5,200 rpm and 553 lb·ft (700 N·m) from 2,600-4,600 rpm. Assistant chief engineer John Rydzewski said premium-unleaded fuel is required to achieve those output figures. The fueling system is a high-pressure (5,076-psi) direct-injection system and compression ratio is 9.8:1. Engineers told Automotive Engineering that the comparatively high pressure of the DI system meant they could forego the current trend of coupling direct- and port-injection fuelling systems.
The “Hot V” difference
Perhaps the new 4.2-L V8’s signature design feature is “reverse” porting that sees the exhaust ports on the inside of the engine’s 90-degree vee, with intake charge entering the cylinders from ports on the outside of the vee.
This is not a first for production-vehicle V8s, but the Cadillac engine takes the concept to a new extreme, locating not only both twin-scroll turbochargers in the engine vee (as integral parts of each exhaust manifold), but also the single-volume catalytic converters, bringing a new definition to the term “close-coupled” in relation to the catalysts. The catalytic converters, drilled for inclusion of an oxygen sensor, literally sit atop the engine and all but inside its valley. Once the exhaust leaves the converter, there are no other components or restrictions on the route to the dual exhaust tips at the rear bumper.
Rydzewski said the “Hot V” design is “the most effective way to optimize the turbo responsiveness of the system.”
The compact twin-scroll turbochargers are supplied by Mitsubishi Heavy Industries (MHI) and feature electronic wastegate control; the titanium-aluminide turbines can spin at up to 170,000 rpm and are half the weight of a similar design in Inconel material, GM said. Maximum boost pressure is 20 psi and the air-to-liquid intercooler design can reject up to 20 kW of heat per cylinder bank, dropping intake-charge temperature by as much as 130 deg (74 C), Cadillac said.
Extracting the immense heat developed in the engine vee was one of the most challenging aspects of the new V8’s development, added Lee. He said the clean-sheet design allowed new thermal-management solutions to assure the V8 maintains acceptable temperatures, particularly after the engine is shut down and the turbochargers and catalysts retain immense amounts of heat. Lee said the single front cooling fan continues to circulate ambient air over and around the engine, while the variable-flow water pump also circulates coolant for whatever time is required after engine shut-down.
With cylinder bores just 10 mm (0.4 in) apart, Cadillac’s new V8 packages its 4.2 liters of displacement in a footprint that’s about 50 mm (2 in) shorter than usual, said Lee. Bore is 86 mm and stroke is 90.2 mm; Lee said the tight spacing between bores did not dictate a limitation on bore size.
The V8’s 6-bolt main-bearing cylinder block is A319 aluminum with pressed-in iron liners and the cylinder heads are Rotocast-supplied 356 aluminum, with 36 mm intake valves and sodium-filled 29-mm exhaust valves. The crankshaft is forged steel, as are the connecting rods.
Performance and refinement were paramount design targets for the 4.2-L V8, but the architecture includes several fuel-saving technologies.
Most significant is Active Fuel Management in its first use for a GM-made DOHC V8. The setup operates the engine in 4-cyl. mode when appropriate, shutting down the outboard two cylinders of one bank and the inner two cylinders of the other engine bank. The variable valve timing allows for 55 deg of authority for exhaust valves and 70 deg of authority for intake. This and other engine-operating parameters are governed by a new E86 engine-management controller.
The new engine also incorporates start-stop for increased fuel saving, although Lee said it remains too early to release projected fuel-economy figures.
For the 2019 CT6, either variant of the new V8 will be coupled with the GM Hydra-Matic 10-speed automatic transmission with GM’s Performance Algorithm Shifting/Performance Algorithm Liftfoot (PAS/PAL) and steering-wheel paddle shift control. An electronic console selector frees interior space by eliminating mechanical linkages.
Additionally, the CT6 applications will include all-wheel-drive as standard fitment with the new V8. The AWD transfer case is mounted integrally with the engine’s cast-aluminum oil pan.
Hand-made in Kentucky
Cadillac’s new 4.2-L V8 will be hand-assembled at GM’s Performance Build Center in Bowling Green, Kentucky. This is the site of assembly for Chevrolet’s Corvette and certain hand-built engines for that model.
It has long been rumoured that the next-generation Corvette could be powered by a new V8 engine—other than its longstanding small-block OHV V8—in addition to the possibility of either adding or wholly moving to an advanced mid-engine vehicle architecture. With the obvious power and torque “headroom” of the new Cadillac V8 and its new assembly location in the same plant where the Corvette and special Corvette engines are built, many will find it logical to speculate that Cadillac’s new V8 architecture is foreshadowing its eventual use for the Corvette—or other Cadillac models.
The company’s powertrain engineers of course aren’t directly addressing that speculation, but Lee didn’t exactly throw cold water when telling the media that the new Cadillac V8 “could be the basis for a lot of other things going forward.”Continue reading »