Although the CT6 flagship sedan has been making do with the same four- and six-cylinder engines that power its lesser siblings, Cadillac has been itching to go toe-to-toe with the best A-list German sport sedans. Boss-man Johan de Nysschen or his immediate predecessor managed to convince the corporate purse-string minders that a high-torque hot-V twin-turbo DOHC V-8 was the price of entry to this elite club, and that dagnabbit, that price was worth paying! So sure enough, sometime in the first half of next year, the 2019 Cadillac CT6 V-Sport will offer the brand’s first exclusive engine since the Northstar. One irony before we delve into the deets: At least initially, the engine will only be offered in the U.S., Canada, and the Middle East, leaving the autobahns unchallenged.
As noted, this 4.2-liter engine, internally code-named GF18, is a clean-sheet design adhering to most of the latest trends. It features a smaller 86.0mm bore and longer 90.2mm stroke, a strategy that favors low-end torque, tolerates higher compression (9.8:1—pretty high for a boosted engine), and leads to improved thermal efficiency. It also enables closer bore spacing—96.0 mm, down from the Small Block’s 111.7 mm, which shortens the block, crank, and all four cams for significant mass savings. Speaking of the crankshaft, it and the eight connecting rods spinning it are made of forged steel and the piston pins feature a diamond-like coating to withstand stress and reduce friction.
The valvetrain includes cylinder deactivation of the number 2, 3, 5, and 8 bores. There’s variable timing on all four cams with 55 degrees of adjustability on the exhaust side and 70 degrees on the intake side. Even better, when switching the engine off (auto stop/start is standard), the intake cams park at a position in the middle of their travel affording no exhaust/intake valve overlap for easier starting and a smoother initial idle. Fuel is always injected directly into the cylinder at high pressure (up to 5,000-plus psi), as there were no operating conditions requiring the addition of port injectors.
The cast stainless steel exhaust manifolds incorporate the housings for the twin-scroll Mitsubishi Heavy Industries turbochargers. The titanium aluminide turbine wheels (half the weight of Inconel) spin up to 170,000 rpm to produce as much as 20 psi of boost that gets relieved via electric wastegates. Bolted directly to the back of each turbo is a 19-liter catalytic converter. These two cats provide all the after-treatment the engine needs—and they greatly complicate the under-hood thermal management, which includes electric fans and water pumps that will continue running long after engine shut-down, following a session of prolonged hard use. An intercooler mounted just above each cylinder head reduces the charge air temperature by 130 degrees F immediately before it whooshes into the outboard intake valves. (Perhaps needless to say, this engine requires premium fuel.)
Two variants of the engine will be offered—each of which will be hand-assembled and personally signed on the Performance Build Center line at the Bowling Green Kentucky Corvette plant. The top version will produce 550 hp at 5,700 rpm and 627 lb-ft at 3,200-4,000 rpm, or 500 hp at 5,000-5,200 rpm and 553 lb-ft at 2,600-4,600 rpm. The difference is primarily in the tuning, with the only mechanical difference being a more restrictive (quieter) exhaust on the lower-output version. That compares reasonably well with the German hot-V twin turbos, including Mercedes-AMG’s 4.0-liter (469-603 hp and 479-664 lb-ft depending on application), Audi’s 4.0-liter (450-605 hp and 406-516 lb-ft), and BMW’s 4.4-liter (552-600 hp and 500-553 lb-ft).
Both variants will come bolted to a 10-speed automatic transmission and feature all-wheel drive to ensure every pound-foot of leverage gets a purchase. The transmission will include the very latest Performance Algorithm Shift programming to ensure it’s always in the right gear, even when you lift for a turn.
It’s interesting to note that Cadillac claims the 2019 CT6 V-Sport’s engine is both smaller on the outside and lighter than the supercharged LT4 and LT5 Small Block V-8s, weighing in at a claimed 529 pounds. Small enough to squeeze into an ATS engine compartment? “I’ve never been asked to look at packaging it in an ATS,” replied assistant chief engineer John Rydzewski. It would certainly fit in an Escalade engine bay and go a long way toward differentiating that truck from the Yukon Denali that’s forever nipping at its Manolo Blahnik wedge heels. Expanding availability to the Escalade would certainly pay off the development costs a lot more quickly than the 1,500 or so engines per year that are currently forecast for the CT6, but truck volumes would surely nix the handcrafted one person/engine assembly idea.
We’re not sure what the engine will be called (for now it’s unimaginatively dubbed Twin Turbo V-8), or how vehicle badging may differ to distinguish the power levels. Also unknown—whether there will ever be a straight-out CT6 V, and if so whether it will use this engine. We were led to believe there is a bit of “head room” to stretch output of this engine, perhaps by de-stroking it to 86mm (4.0 liters) and spinning it a lot faster. For now, we’re assured that this engine targets a more refined power than a V badge portends.
Stay tuned, as some of these questions may be answered when the freshened 2019 Cadillac CT6 breaks cover at the New York auto show on March 28.