Light-duty pickups, SUVS, and other large vehicles to get all-new diesel after 2009.

“Diesel is critical to GM’s global strategy,” Tom Stephens, vice president of GM Powertrain division said in August at an introduction of an all-new diesel V-8 engine to executives and journalists. The company says the new engine meets BIN 5 requirements for 2010, which are much more stringent than BIN 5 levels for 2007. Our first impressions are that the all-new V-8 is gutsy, smooth, quiet, clean, which we experienced from a drive in a current model Buick Ranier mid-size SUV fitted with the new engine. 


Front and side of new engine is silhouetted against small-block gas engine

Because we were not allowed to look under the hood of the Ranier, which had a large 18-inch square bulge on its right side, protruding about three inches tall, we’re guessing it displaces 4.5 to 5.0 liters. We’re also guessing it’s a pushrod engine, because most important to GM is to keep the price of the engine low, and the size compact enough to fit in mid-size SUVs. GM did say the engine is compacted graphite iron (CGI) with aluminum cylinder heads that have integrated manifolds. Connecting rods and caps are fracture split, a common GM method for keeping fit tolerances accurate. The injection system is common-rail, as well.

To meet emissions, the engine uses an oxidizing catalyst, followed by an SCR (selective catalytic reduction) catalyst, and then a particulate filter about the size of a large pickup muffler. “Today is a solution that meets the NOx challenge,” said Charlie Freese, head of diesel engineering for GM. Freese added that the new engine is “more than 3.0 liters and less than 6.6.”

The SCR system was chosen for its flexibility with different qualities of fuel, Freese said. “Liquid urea is what we use. Our intention is to size the tank to span one oil change interval.” Freese said that size would be about five to seven gallons, which would add about 40 to 55 pounds to the vehicle.


Photos and details of the new engine are still a secret at GM

New engine will have variable turbocharging, but Freese would not say if it would be a single, double, or even a tri-turbo system.

Two days before the engine was introduced to journalists, it was driven by GM top executives, who made comments regarding the low noise and good launch feel, according to engineers. To us the engine was reminiscent of Audi’s 4.0-liter diesel V-8, except the GM engine is claimed to meet 2010 BIN 5 emissions standards, which the Audi cannot presently meet.

The engine was only running in the test Ranier a week before the demonstration drive, although it has been in development for more than a year. It is mated to a six-speed automatic, but a new version of the new rear-drive six-speed family—which are the 6L45, 6L50, 6L80, and 6L90—that are being introduced for 2007.

Cruising on a level road in sixth gear, the engine revved at 1500 rpm at 56 mph. At part throttle acceleration it shifts from 1500 to 2000 rpm, and would get into fifth gear by 35 mph. The tall gearing and low-revving steady torque output is consistent with V-8 diesels from BMW and Audi, but something unusually refined for a Buick SUV. The maximum torque output of the new engine is 520 lb ft beginning at 1800 rpm and staying strong up to 4500 rpm. The new engine is promised to “deliver industry leading power and torque and refinement in noise and vibration,” said Freese. “It hits peak torque at 1800 rpm and goes out to 4500 rpm.”

In addition, Freese promises “this engine is going to be at benchmark levels for noise and vibration.” So far we feel GM has hit that mark. The engine produces 330 hp, according to Freese.

We noticed some diesel combustion rattle noise—characteristic to all diesels and a product of the way combustion occurs—but it can be heard only from outside and behind the vehicle. Inside there is no telltale diesel noise, apart from brief constant-speed whine events from the turbo. The engine was running on ULSD (ultra low sulfur diesel) fuel available in the U.S. , said engineers, not a cleaner GTL (gas-to-liquid) blend or other more highly refined fuel more common in Europe .

Launch speed is impressive, although immediate take-off from a stop feels a bit bogged down. Engineers explained that the traction control system was calibrated to clamp down on the launch because wheelspin and axle tramp would otherwise result. Above 5 mph, the diesel-equipped Ranier pulled strongly, and at full acceleration shifted just above 4000 rpm in the middle gears of the six-speed.

On one zero-to-60 mph sprint, the Ranier took about ten seconds, however, that was with five adults on board, with the aggressive traction control system engaged.

The engine is an all-new GM design, not a version of anything from Isuzu, which is where the previous generations of the 6.6-liter Duramax came from. The engine is destined to be used in vehicles “under 8500 lb GVW”, said Tom Stephens, vice president of GM Powertrain division.

General Motors’ direction is to put diesels in large vehicles and focus on optimizing gasoline engines for small vehicles. “Diesel would pay back earlier for the big truck,” says Freese, “The Saturn Green Line hybrid would pay back earlier than a diesel.”

New diesels will cost “several thousand” dollars more than comparable previous diesels not subject to the stringent new emissions standards.

The mid-size Buick Ranier was originally developed for a family of inline engines, five and six cylinders, and the current gasoline 5.3-liter is a tight fit inside the engine compartment. Fitting the new diesel engine inside this space was of great importance to GM, said Freese. “To really be able to have maximum flexibility in how we use this powertrain, it has to fit in the envelope of the gasoline small-block engine. It gives us a lot of flexibility to introduce this powertrain,” he explained. “This is just a mule, not a vehicle that will go in production. This is intended to show this powertrain fits under the hood.”