Engine: Description and Operation
Engine Component Description
The Northstar V8 VIN Code D is a 4.4L (267 cu in) supercharged engine incorporating two intake and two exhaust valves per cylinder with individual cylinder head mounted camshafts with camshaft position actuators for intake and exhaust functions (DOHC). The cylinder bore diameter is 91 mm (3.583 in) and the piston stroke is 84 mm (3.31 in). The cylinders are arranged in two banks of four with a 90 degree included angle. The left, front, bank of cylinders are number 2-4-6-8 and the right, rear, bank cylinders are 1-3-5-7. Engine firing order is 1-2-7-3-4-5-6-8.
Crankcase
The cylinder block is constructed of aluminum alloy by the precision sand casting method and is constructed of two sections, an upper and a lower crankcase, split at the crankshaft center line. The grey cast iron cylinder liners are cast with the upper crankcase. The upper and lower crankcase sections are held in alignment by four dowel pins. Once machined, the sections must be kept together as a set. Sealing between the crankcase halves consists of a silicone rubber seal and a bead of anaerobic sealant along each side. Since the lower crankcase contains the lower main bearings, this casting adds to the structural rigidity of the engine assembly. Both upper and lower crankcases incorporate oil drain back passages isolated from the crankcase. These passages provide a direct path from the cylinder heads to the oil pan in order to prevent the needless aeration of the oil through contact with the rotating components. An oil gallery through the block supplies four oil jet assemblies used to cool the cylinder pistons. The assembly is bolted between two cylinders and incorporates two jets. Each assembly contains a spring operated check valve to maintain proper oil pressure.
Crankshaft
The crankshaft is a forged steel design with five main bearings. Crankshaft thrust is taken by the number three main bearing. The position sensor, also known as the reluctor wheel, is integral with the crankshaft. The crankshaft is internally balanced and incorporates a one piece rear seal. A rolled fillet radius is incorporated on all bearing journals to improve fatigue strength.
Connecting Rods and Pistons
The connecting rods are made from forged ferrous powder metal and have full floating piston pins. These pins are slip fit in the bronze bushed rods and are retained in the piston by round wire retainers. The cast hypereutectic aluminum alloy pistons use two low tension compression rings and one multi-piece oil ring. The top compression ring is nitrided steel. The second compression ring is coated cast iron. The oil ring is a three piece side seal type ring which incorporates a steel expander and two chrome plated steel rails. To provide a non-scuffing surface when the engine is new, the pistons are tin plated. The piston skirts are coated with a polymer coating to provide reduced friction.
Camshaft Drive System
The four overhead camshafts are driven by three separate fine pitch chains. The primary drive chain connects the crankshaft with the intermediate shaft and sprocket located directly above the crankshaft behind the engine front cover. Each camshaft drive chain connects the intermediate sprocket with the camshaft position actuators on each intake and exhaust camshafts on the cylinder heads. Two camshaft drive chains are used; one for each cylinder head. Each of the chains incorporates a hydraulic tensioner to minimize chain noise and provide accurate valve action by keeping slack out of the chain and continuously adjusting for chain wear. This is accomplished by providing engine oil pressure to each tensioner forcing a nylon pad into mesh with the slack side of the chain. As the chain stretches from wear, a ratchet mechanism inside the tensioner prevents the nylon pad from retracting when the engine is turned off and engine oil pressure ceases.
Camshaft Position Actuator System
The camshaft position actuator system is an electronically controlled and hydraulically actuated system. The camshaft position actuator system enables the engine control module (ECM) to change camshaft timing of all four camshafts hydraulically while the engine is operating.
Two camshaft position actuator magnets, one for each camshaft position actuator oil control valve, are mounted to a camshaft position actuator housing on the front of each cylinder head. The ECM energizes the camshaft position actuator magnet in order to create a magnetic field. The magnetic field created by the camshaft position actuator magnet pulls, from the home position, the spring loaded spool valve in the center of the camshaft position actuator oil control valve. The camshaft position actuator oil control valve is incorporated into the fastener that bolts the camshaft position actuator to the camshaft. Alignment between the camshaft position actuator magnet and the camshaft position actuator oil control valve is crucial. An air gap must be maintained between both components.
Oil under pressure is supplied to the front camshaft bearing cap and flows through passages into the camshaft front journal. The camshaft front journal passages supply oil to the camshaft position actuator oil control valve. The camshaft position actuator oil control valve supplies oil to the camshaft position actuator. The camshaft position actuator oil control valve incorporates a return spring in order to return the internal spool valve to the home position.
The camshaft position actuator contains an inner rotor with vanes bolted to the camshaft and an outer housing incorporating the timing drive chain sprocket and camshaft position sensor trigger wheel. Internally the camshaft position actuator contains a spring loaded locking pin that prevents movement between the inner rotor and outer housing and keeps the camshaft position actuator in the home position. The locking pin releases when proper oil pressure reaches the camshaft position actuator. The exhaust camshaft position actuators also incorporates return springs in order to return the exhaust camshaft position actuators to the home position when the engine is turned off. Due to rotation direction of the intake camshaft position actuators return springs are not necessary.
Oil directed by the camshaft position actuator oil control valve's position is used to vary the advance or return of the camshaft position actuator's vanes from the home position.
Cylinder Heads
The cylinder heads are semi permanent mold cast aluminum with powdered metal valve seat inserts and valve guides. Two 36.2 mm (1.425 in) intake valves and two 29 mm (1.142 in) exhaust valves are actuated by roller finger followers pivoting on a stationary hydraulic lash adjuster (SHLA). Separate intake and exhaust camshafts are supported by five bearings machined into the cylinder head with camshaft thrust taken by the first bearing. The combustion chamber is roughly in the shape of a clover leaf with a nominal volume of 58.08 cc (3.544 cubic inch) and a centrally located spark plug. The exhaust ports are specially polished using an abrasive flow machining method. The cylinder head gaskets are multi-layer steel (MLS).
Engine Cooling System
The coolant pump assembly is located on the engine front cover. The water outlet housing distributes coolant to the cylinder block and collects it from the cylinder head for delivery to the radiator.
Lubrication System
Notice: This engine uses a special high performance oil filter. Use of any other filter may lead to filter failure and/or severe engine damage.
The oil pump has increased output from other Northstar engines. The additional output is needed to supply the volume needed for the oil jets required to cool the pistons. An oil gallery, specific the LC3, is used to supply oil to the oil jets. A new oil filter is also required to meet the additional volume that needs to flow from the oil pump. The new oil filter incorporates a bypass valve and a specific filtering media for improved protection along with lower pressure drop through the oil filter. Supercharged Northstar engines oil filter adapters and oil filters utilize special thread size and pitch. The oil filter adapter does not contain the bypass valve.
Supercharger and Induction System
The induction system consists of induction tubes, throttle body, and a Roots style supercharger with an integral intake manifold and intercooler. A forward section to the induction system consists of a central intake port that splits into twin thin wall cast aluminum induction tubes. Each tube incorporates a silencer in order to reduce induction noise without disrupting air flow. After each silencer a flexible port duct connects to the rear tube that combines the air flow into a single port at the rear of the engine. A flexible port duct connects the rear tube to the 80 mm (3.15 in) diameter throttle body mounted at the rear of the supercharger.
The throttle body is an electronic throttle controlled (ETC) design. The throttle body, EVAP purge valve solenoid, and bypass actuator cable mount to the supercharger bypass valve.
The supercharger pulley is driven by a serpentine drive belt. The pulley drives the supercharger from the front of the engine. The two tri-lobe helical Roots type rotors are counter-rotating as the drive and driven rotors are geared to each other. The rotors are mirror image, precision hobbed aluminum extrusions rotating on press-fit steel shafts. Ball bearings between the gears and the rotors support the rotors at their forward end. The forward bearings are lubricated and cooled by a volume of synthetic gear lubricant contained within the supercharger front cover. At the rear, sealed maintenance-free needle bearings support the rotors. The incoming air enters the rotor chambers at the lower rear just past the bypass valve. Air is pushed up around the outside of the rotors and is expelled from the rotors at the upper front of the supercharger body. Mounted on top of the supercharger body is the intercooler housing. The air flows up from the supercharger and travels through the intercooler tube fins and then down into the individual cylinder inlet runners. The supercharger displacement and pulley ration are proportioned to deliver almost two times the volume of air the engine would naturally aspirate, providing positive manifold pressure when the valve is closed. The bypass valve controls recirculation between the rotor outlet and inlet to reduce parasitic losses and noise during light load operation, at which time the valve is open.
The intercooler housing contains four longitudinal bores that house the four cylindrical intercoolers. The manifolds at the front and rear of the intercooler housing route the coolant through the interior of the four intercooler tubes. A coolant fill cap is located on the top of the intercooler housing. Slots in the intercooler housing direct the supercharged air flow past the fins of the intercooler tubes. Once cooled by the intercooler the supercharged air is directed through the top of the intercooler housing and down into the outboard sides of the intercooler housing and into individual runners that proceed through the supercharger housing and into the cylinder head intake runners. Inputs from multiple sensors for vacuum and pressure and a temperature sensor are used by the engine management system to control the supercharge operation. The bypass valve for the supercharger is operated through a cable by a supercharger bypass valve actuator. The supercharger bypass valve actuator is operated by supercharger pressure and vacuum operated by a charge air bypass regulator solenoid valve. The charge air bypass regulator solenoid valve is controlled by input from the engine management system. A cooling system separate from the engine cooling system is used for the intercooler. An electric remote-mounted coolant pump is used to circulate the coolant between the intercooler of the supercharger and the heat exchanger mounted at the front of the vehicle.
Right and Left Bank Designation
Right hand (RH) and Left hand (LH) designations through the engine mechanical On-Vehicle Service section are viewed from the rear of the engine.