The team that created the Oldsmobile Aurora V8 engine has combined the latest in combustion technology and the most extensive use of computer testing in General Motors' engine history to create the new 3.5-L V6 engine that has its first application in the 1999 Intrigue. The engine uses technology from the Aurora 4.0-L V8 while introducing several new features. From the beginning, the development team started had a "hit list" of specific program goals including good noise, vibration, and harshness (NVH) characteristics; compliance with California Low Emission Vehicle (LEV) emissions standards, on-board refueling vapor recovery, and second-generation on-board diagnostics (OBD-II); commonality, where practical, with the Aurora's V8; maximum engine/transmission integration for vehicle harmony; and use of agile and flexible manufacturing systems for efficiency's sake.

The resulting engine has dual overhead cams and 24 valves. The chain-driven camshaft system provides lifetime durability, with no required adjustments or maintenance. With 24 valves to open and close, friction becomes an issue. This dilemma was solved by incorporating low-friction, rolling-element rocker arms at the camshaft interface. Each end pivot rocker arm is anchored with a stationary hydraulic lash adjuster to maintain correct valve lash automatically. Induction-hardened nodular iron cams could then be used instead of more costly steel cams because contact stresses at the cam lobe were kept low.

The low-volume, high-flow-rate cooling system uses an internal bypass to achieve rapid engine warmup for better emissions, fuel economy, and passenger comfort. The high coolant-exchange rates ensure uniform internal temperatures during warmup and high-output operation, reducing stress on gasketed joints and maintaining the dimensional integrity of internal parts.

The engine delivers 160 kW (215 hp) at 5600 rpm and 312 N•m (230 lb•ft) of torque at 4400 rpm. Aluminum cylinder heads and a 9.3:1 compression ratio were chosen for maximum thermal efficiency using regular fuel. A 3473-cm3 displacement results from a bore and stroke of 89.5 and 92 mm (3.52 and 3.62 in.), dimensions that provide for strong low-end torque.

Mass was reduced by using a cast aluminum two-piece block in addition to aluminum cylinder heads. Cast-in iron cylinder liners provide a durable interface for the aluminum pistons. Splitting the block at the crank centerline allows the main bearing caps and side rails to be cast in a single lower crankcase.

Lightweight, low-friction, hypereutectic cast aluminum pistons with full floating wrist pins are used. Their top rings are located 3.0 mm (1Ú8 in.) from the top of the piston crown to minimize crevice volume for unburned hydrocarbon reduction. The top piston ring is nitrided to withstand the heat better and the top ring groove is hard-anodized for strength.

Three single-row roll-er chains and eight sprockets keep valve timing synchronized. A single primary chain drives the two intake cams and the balance shaft directly from the crank sprocket. Two separate, shorter chain loops connect the exhaust cams with the intake cams. Three guides help to restrain the primary chain, while a hydraulically activated tensioner arm eliminates slack. This layout minimizes packaging requirements and adds very little to the overall length of the engine.

Connecting rods, cam drive sprockets, camshaft bearing caps, valve guides, and valve seats are all made from powder metal for fabrication consistency, minimal machining, and optimum material properties.

A powertrain control module (PCM) monitors and directs both engine and transmission operations. More than 29 sensors, switches, and actuators communicate with the 512-kB PCM computer to provide temperature, speed, position, and location settings for numerous powertrain functions. The PCM is housed in the air cleaner, the fresh airflow providing improved cooling. Its location minimizes the number of wires that must be passed through the instrument panel.

The crankshaft-triggered ignition system features dual crankshaft sensors, a single-cam sensor, and coil-on-plug technology. Its reluctor ring is precision-machined into the parent metal of the crankshaft, providing an accurate reference for crankshaft position. The PCM schedules firing events and ignition energy for each cylinder. The close proximity of the coil to the plug eliminates the need for switching and distributing high secondary voltage, thus enhancing durability.

The engine's 90¡ configuration allows for a shorter engine and a low hoodline and increased packaging space for the tuned, thermoplastic intake manifold. This one-piece manifold has long, individual intake runners connected to a common plenum for good low-speed torque and high-speed flow. A cast iron, split-pin crankshaft with an integral ignition trigger wheel and four main bearings provides even firing, while roller chains and sprockets keep valve timing synchronized for life.

The primary imbalance inherent to a 90¡ V6 is compensated for by a balance shaft in the vee of the block. The counter-rotating shaft is driven by the primary timing drive at crankshaft speed. A hollow-cast manufacturing technique was specified to reduce its mass by more than 1.4 kg (3 lb).

An advanced, composite fuel rail design uses advanced top-feed injectors for fuel delivery as well as a new compact fuel-pressure regulator. The injectors are about half the size and weight of traditional fuel injectors and have a simplified design that reduces the potential for contamination. The fuel rail attaches to the intake manifold without bolts, requiring fewer parts and providing simpler and quicker manufacturing.

Maintenance needs are reduced by DexCool engine coolant, which provides engine protection for up to 240,000 km (150,000 mi.) and 160,000 km (100,000 mi.) platinum-tipped spark plugs. In addition, the PCM continuously monitors engine-operating parameters and calculates useful oil life based on how the car is driven, notifying the driver when to change the oil. This results in longer oil change intervals and less waste-oil disposal.

All accessories are designed for direct mounting to ensure maximum rigidity and minimum noise generation. Powertrain stiffness, another contributor to good NVH characteristics, is enhanced by the structural oil pan that bolts directly to the transmission, eliminating the need for separate stiffening braces at the engine/transmission bell-housing interface. Slosh baffles in the pan keep oil away from the crank, and a contoured scraper sheds oil from the crank to reduce friction.

This engine "ran" in computer simulation more than a year before the first prototype was constructed and started. Analysis covered windage losses, intake fluid dynamics, structural stresses, noise, vibration, and power forecast. Because of the year-long simulations, the development team attained a level of engine testing refinement never before achieved in a new engine, according to John Zinsler, chief engineer for Premium V engines. Complete structural models accurately predicted stresses and strains, and over 60,000 engine dynamometer test hours and 2.4 million km (1.5 million mi.) on vehicle prototypes have confirmed the computer analyses, he said.