Whatever you do, don’t call it Northstar. According to John Rydzewski, assistant chief engineer of the all-new 550-hp Cadillac V-8 engine, the powerplant was called many things during its roughly four-year development, but in the end they’re just calling it exactly what it is: twin-turbo 4.2-liter V-8. No funny alphanumerics or drawing on history here. Considering the Cadillac brand’s devotion to letters and numbers for all of its nameplates except the Escalade, we’re a little surprised something like NS2 didn’t wiggle its way into its lexicon.
General Motors devotees will remember the Northstar as the first and—aside from the engine powering the limited first-gen Corvette ZR-1—the only DOHC V-8 that GM has produced. It was a silky-smooth mill in its day that served in the top-range Caddys, Oldsmobiles, Pontiacs, and Buicks. But this new engine isn’t much like that one.
Starting at the top, it certainly looks different. That’s because the rotocast aluminum heads have a reversed flow, creating what is called a “hot V,” to feed two Mitsubishi Heavy Industries TD03 twin-scroll turbochargers nestled in the valley of the engine. This arrangement is common among the German automakers, with Audi, Porsche, Mercedes, and BMW all running hot-V twin-turbo V-8s. Positioning the turbos as close to the exhaust ports as possible is advantageous to response and efficiency, and it also simplifies exhaust plumbing to allow the turbos to receive even exhaust pulses from a cross-plane V-8. Air-to-liquid intercoolers also located atop the engine reduce the intake temperature before the air makes its way through cast aluminum intake manifolds and into the cylinders.
The sandcast aluminum block is a clean-sheet design, according to Cadillac, and it is fitted with a 10-quart sump, cross-bolted main bearing caps, a forged steel crankshaft and connecting rods, pistons from Mahle, and 5000-plus-psi direct fuel injection. The compression ratio is 9.8:1. The exhaust manifolds are integrated with the hot side of the turbo housings, which encase titanium turbine wheels spinning at up to 170,000 rpm while pressurizing the intake manifolds with as much as 20.0 psi of boost.
Both intake and exhaust camshafts feature cam phasers. Hydraulic lifters acting on roller finger followers can deactivate valves, enabling cylinder deactivation and V-4 operation to save some fuel. The 4.2’s default firing order is 1-5-4-3-6-8-7-2, which is different from that of GM’s venerable small-block engine, and then changes to to 1-4-6-7 in V-4 mode.
Cadillac says the new 4.2 is actually a little lighter and a little more compact than the LT4. We find this hard to believe, considering compact dimensions are among the biggest selling points of GM’s small-block. Engineers point to the shorter block (by 50 mm), made possible by bore spacing down to 96.0 mm from 111.7 mm in the small-block.
For now, this new 4.2 will live exclusively in the Cadillac CT6. It will launch in the freshly unveiled CT6 V-Sport with an estimated 550 horsepower at 5700 rpm and 627 lb-ft of torque from 3200 to 4000 rpm. (Ninety percent of the torque is available as low as 2000 rpm.) That’s breathtaking torque, as in it takes the breath out of the competition. The 553-lb-ft BMW M5 is the closest, but an M5 beater the CT6 V-sport is not. Its mission isn’t too dissimilar from that of a V-8–powered Mercedes-Benz S-class, which is to deliver ultrasmooth and quiet operation while still being able to outrun the vast majority of cars on the road when called on.
After the V-Sport launches, a 500-horse version of the 4.2 will join the CT6 ranks sometime in the first few months of 2019, with the only differences being a slightly different exhaust and ECU tuning. All V-8–powered CT6s will receive the 10-speed automatic transmission and an all-wheel-drive transfer case. The front axle runs through the oil pan, ensuring the engine is mounted mostly behind the axle line for optimal weight distribution. While Cadillac’s representatives won’t talk about future product, they made it clear to us that there is potential left untapped in the engine to make an even more powerful version.
Character, specifically under-the-radar smoothness, is the reason for a Cadillac-only V-8. Sure, Cadillac could have slapped an equally powerful small-block in the CT6’s bay and been done with it. While a pushrod V-8 is a very versatile engine, subtlety isn’t on its résumé. Brand president Johan de Nysschen, formerly of Infiniti and Audi, was brought on board to make Cadillac a serious player in the luxury segment. To succeed, Cadillac needs special elements, things it can call its own, and a Caddy-only V-8 is a great start. We can’t wait to see what’s coming next.
from Car and Driver BlogCar and Driver Blog http://ift.tt/2ptq9uO
via IFTTT
0 comments:
Post a Comment