Think of General Motors' new global four-cylinder engine as the camel of the auto industry: a perfect example of a design by committee that works.
The engine is an amalgam of compromises, design trade-offs and sundry technologies reflecting its creators' diverse backgrounds. Designers realized early that without certain basic design elements, the engine had no chance for success in any market.
For starters, it had to be quiet and refined. That's a challenge in larger-displacement four-cylinder engines. In these powertrains, the heavier moving parts can increase the natural tendency of inline fours to vibrate.
Like many of its competitors, the L850 has balance shafts to stamp out these vibrations. Located in the block just above the crankshaft, the two shafts are weighted unevenly and turn at twice the speed of the crankshaft. As they turn, they generate opposing vibrations to counteract the vibrations caused by the moving pistons.
The L850 also borrows the Northstar's low-friction roller finger-follower valve lifters. These lifters have small wheels instead of pads to follow the contours of the turning cam lobe. By reducing friction, the design saves fuel and helps smooth the engine.
CUTTING THE CLATTER
Further refinement comes from bolting accessories such as the alternator and air-conditioning compressor directly to the engine block. These hard mounts cannot vibrate and clatter as adjustable brackets would.
Another goal for the L850 was compactness.
True, the engine's first home is the cavernous engine bay of the 2000 Saturn LS, which also must swallow a V-6. But smaller vehicles such as Opel's Vectra and Astra will follow, and older GM models also might get retrofits.
To avoid the expense of re-engineering those vehicles, the L850 had to be no larger than GM's other four-cylinder engines.
That's not a problem with the Pontiac Grand Am's bulky LD9, but the 2.2-liter pushrod LN2 in the Chevrolet S10 pickups, Chevrolet Cavalier and Pontiac Sunfire is a very squat knob of iron.
Engineers created a 3-D packaging envelope for the L850 by overlaying the schematics of GM's current lineup of four-cylinder engines. The composite included the 1.9-liter Saturn SL/SC engines and the current family of Opel Ecotec engines. It established dimensional borders for the L850 that could not be crossed.
Engineers shaved millimeters wherever possible to make the L850 fit. For example, the designers spaced the pistons more tightly by using iron cylinder liners with walls just 1.5 millimeters thick.
REDUCING THE WEIGHT
One happy consequence of all this cutting and shaving is reduced weight. The L850 weighs only 330 pounds fully 'dressed' with accessories, compared to 418 pounds for a dressed 2.4-liter LD9.
Unlike many transverse-mounted four-cylinder engines, the L850's intake faces forward while its exhaust faces rearward. The layout helps the engine meet federal emissions standards by bringing its exhaust manifold closer to the catalytic converter for quicker light-off.
That reduces emissions during the first two minutes the vehicle is in use, when the engine is still cold.
The L850 visually resembles the current Saturn 1.9-liter engine because of its lost-foam aluminum castings.
In the lost-foam process, the casting cores are made from plastic foam that vaporizes as the molten aluminum alloy flows into the die. Although it is used to produce the current Saturn engine, the process was re-evaluated for the L850, says GM Powertrain's Jay Subhedar, one of the engine's chief engineers.
GM is continuing the lost foam process in part because it lets engineers cast intricate oil filter channels into the block. It would have been impossible to machine those passages, Subhedar said.
The oil filter is a cartridge type that screws in from above, allowing technicians to change the filter element without crawling under the car.
The L850 filter is GM's first step toward 'over-the-fender' oil changes, says Al Landosky, Saturn's advanced powertrain engineering manager. The company also is working on dipsticks that will suck oil from the crankcase, he says.
Engines built in North America and Europe will share 85 percent of their parts, but there will be differences. Gearing of the U.S. engines will be substantially lower to suit the tastes of American drivers, who like quick getaways from the stoplight.
Also, European units will run a 10-to-1 compression ratio while U.S. counterparts will be limited to a 9.5-to-1 compression.
It was one compromise necessary to accommodate some of the cut-priced gasolines available here, says Subhedar.
'Customers don't make the connection between poor fuel quality and their engines not running well. They just think GM screwed up.'