Tech & Trends
BILL VISNIC Ward's AutoWorld, Dec 1, 2000 12:00 PM

Inlines Alive! GM revives the inline-six engine - in volume Have hope. The world has yet to be vanquished by vee engines.

Thank General Motors Corp. for resuscitation of the industry's most tragically abandoned engineering triumph: the indiscreetly smooth inline 6-cyl. engine. Until now, renowned engine-maker extraordinaire BMW AG was left as practically the sole keeper of the faith.

Thank Ron Kociba, too. He's GM Powertrain's chief engineer for the all-new Vortec 4200 inline 6-cyl. truck engine. A wool-dyed "engine guy," Mr. Kociba concedes that the easy route would have been to design "just another" V-8.

Instead, he and his team opted for the unconventional: a DOHC I-6 configuration that would perform like a V-8 but provide the NVH and manufacturing advantages inherent with the I-6 layout.

Powertrain sources indicate the Flint Engine South facility in Flint, MI, (investment: $500 million) has capacity for 2,100 units per day, or approximately one-half million engines annually. A similar investment of $500 million for an expansion of GM's Tonawanda, NY, engine plant will allow that plant to add production of the new inline engine family to its current build of the L850 "global" 4-cyl. engine.

With that kind of volume, the inline six layout once again will be a force in the market.

The Vortec 4200 is GM's first inline 6-cyl. for trucks in more than 15 years. And GM phased out inline 6-cyl. engines entirely in 1993 - so Mr. Kociba describes the decision to build a new-generation inline six as "pretty radical."

The Vortec 4200 represents other firsts for GM: first all-aluminum engine for light trucks (until now, all GM light truck engines have been constructed with iron blocks), and it is the first GM engine of any kind to use variable valve timing.

The 4.2L DOHC Vortec is slated for initial use in GM's fully redesigned `02 midsize sport/utility vehicles (SUVs): the Chevrolet Trailblazer, GMC Envoy and Oldsmobile Bravada.

Mr. Kociba says the Vortec 4200's DOHC configuration dispels the myth that DOHC designs and load-pulling torque for trucks just don't mix. The Vortec 4200 "isn't just a `top-ender,'" he boasts, citing the development of 90% of peak torque as low as 1,600 rpm and keeping that 90% available well past the torque peak.

The Vortec 4200 produces 270 hp at 6,000 rpm and 275 lb.-ft. (373 Nm) of torque, peaking at an easygoing 3,600 rpm.

A key feature is variable valve timing for exhaust valves, which engineers say helps in delivering the Vortec's wide band of power and provides improved idle quality. Phasing of the exhaust cam also meant that the exhaust gas recirculation (EGR) valve was eliminated: All EGR function is handled by the varying exhaust-valve timing. Including this function, says Mr. Kociba, also provides a meaningful 25% reduction in engine-out hydrocarbon (HC) emissions.

Other design highlights include electronic throttle control (ETC), a unique and effective multi-layer head gasket, true coil-on-plug ignition and a powertrain control module (PCM) mounted directly on the intake manifold. In placing of the PCM, engineers point out another I-6 advantage: the well-defined hot-and-cold sections of the engine. Heat-sensitive components can be located on the "cold" side of the engine, well away from the hot exhaust.

Engineers also are proud of the engine's carefully optimized combustion: The Vortec 4200 runs an advantageous 10:1 compression ratio, yet doesn't require premium gasoline.

Mr. Kociba says the engine's 270 hp exceeds that of all other light truck 6-cyl. engines on the market - and in most cases, V-8s too. In addition to a raft of import nameplates, competitive vehicles include Ford Motor Co.'s 4.6L V-8 Explorer (240 hp) and DaimlerChrysler AG's Dodge Durango (a choice of V-8s producing 235 hp or 245 hp). Typically, however, competitors' V-8s do produce more torque than GM's new 6-cyl. unit, and torque remains an important measure for buyers who engage in serious towing.

He adds that the new Vortec engine enjoys around 5% better fuel economy and a 25% reduction in hydrocarbon emissions when compared to the 4.3L OHV V-6 engine used in GM's current midsize SUVs.

Fully dressed, the engine - including all of its direct-mounted accessories and catalysts - weighs 430 lbs. (195 kg); using more-commonly quoted weight, in "as shipped" trim, the engine weighs 408 lbs. (185 kg). That, say Powertrain engineers, is 40 lbs. (18 kg) lighter than the current 4.3L V-6 and a hulking 100 lbs. (45 kg) lighter than competing light truck V-8s.

GM Powertrain officials say early January sees the production startup of the newly constructed Flint Engine South facility. It's the first home of Vortec 4200, a modular engine family that GM engineers say eventually will include DOHC inline 4- and 5-cyl. engines of varying displacements - and eventually will replace GM's 3.4L and 4.3L OHV V-6 truck engines.