3.2L Pentastar V6 engine (2014-on)

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Introduction

The 3.2L Pentastar V6 engine was first introduced in the Jeep KL Cherokee in 2014 and was the first derivative of the 3.6L Pentastar V6 engine. Key features of the 3.2L Pentastar V6 engine included:

• High-pressure die-cast aluminium block with a 60-degree ‘V’ angle;
• Nodular iron crankshaft;
• Forged steel connecting rods;
• Cast aluminium alloy pistons;
• Semi-permanent mould cylinder head made from T7 aluminium;
• Double overhead camshafts (chain-driven);
• Variable intake and exhaust cam phasing over a range of 50 degrees;
• Four valves per cylinder actuated by roller finger followers;
• Port injection via four-hole injectors;
• Compression ratio of 10.7:1; and,
• Total length of 503 mm.

The Pentastar V6 engines are manufactured at three locations:

• Mack Avenue Engine Complex in Detroit, Michigan;
• Trenton Engine Plant in Trenton, Michigan; and,
• Saltillo South Engine Plant in Mexico.

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Block

The 3.2L Pentastar V6 engine had a high-pressure die-cast aluminium cylinder block with an open-deck design. The 3.2L Pentastar V6 engine had 91.0 mm bores and an 83.0 mm stroke for a capacity of 3239 cc. Compared to the 3.6L Pentastar V6 engine, the 3.2L version had thicker cast iron cylinder liners to reduce the bore from 96.0 mm to 91.0 mm.

As a result of its high-pressure, die-cast manufacture, it is estimated that the Pentastar block was around 9 kg (20 lbs) lighter than GM’s ‘Alloytec’ engines, resulting in a saving on aluminium of around $40 USD per engine.

Due to its 60 degree ‘V’ angle, the 3.2L Pentastar V6 engine did not require balance shafts.

Crankshaft, connecting rods and pistons

The 3.2L Pentastar V6 engine had a nodular iron crankshaft that underwent a rolled fillet process. The crankshaft weighed 19.5 kg (43 lbs) and had four bolts on the main bearing supports, while two additional bolts were cross-fitted in the main bearing caps for a rigid bottom end. Specifications for the crankshaft were as follows:

• Main bearing cap material: powdered cast iron;
• Crankshaft journal width: 72 mm; and,
• Crank pin width: 59 mm.

A structural windage tray was used to reduce oil splash on the crankshaft and reduce power losses from the reciprocating assembly.

The 3.2L Pentastar V6 engine had forged steel connecting rods and cast aluminium alloy pistons which weighed 359 grams (+/- 5 grams). Attributes of the pistons included:

• Low-friction piston rings;
• Reduced skirt area;
• Full-floating piston pins with an offset of 0.8 mm; and,
• Three oil cooler jets mounted in the engine block which sprayed oil onto the pistons to reduce heat and suppress knocking tendencies. Each jet cooled two pistons and was attached to the main oil gallery.

Cylinder head and camshafts

The 3.2L Pentastar V6 engine had a semi-permanent mould cylinder head – made from T7 heat-treated aluminium – and chain-driven double overhead camshafts (DOHC). The chain drive of the 3.2L Pentastar V6 engine had four chains, each of which had a ‘silent chain link’ design to improve sprocket engagement and reduce noise. While one chain drove the oil pump, the other three chains drove the camshafts. The primary and secondary camshaft chains used oil pressure-controlled chain tensioners; while the left secondary used a ratchet, the right secondary chain and primary chain did not. The chain guides and tensioner arms were made of glass-filled nylon, with nylon wear faces.

The 3.2L Pentastar V6 engine had high-flow intake and exhaust ports, while the exhaust manifold was cast into the cylinder head. Unlike the 3.6L Pentastar V6 engine, however, the 3.2L version had individual exhaust-manifold runners to reduce weight and for more compact packaging.

Cam phasing

The 3.2L Pentastar V6 engine had independent cam phasing for the intake and exhaust camshafts over a range of 50 degrees relative to the crankshaft. The torque-actuated phasers used the natural action of the valve springs to pump the phasers into position, lowering the amount of energy required to move the phasers. According to Chrysler, the small size of the phasers combined to reduce weight and allow the camshafts to be spaced closely together for optimum valve angles and combustion chamber geometry.

Valves

The 3.2L Pentastar V6 engine had four valves per cylinder that were actuated by roller finger followers with hydraulic lash adjusters. The single-piece intake valves were made from forged, heat-resistant (martensitic) steel, while the two-piece exhaust valves had a forged austenitic head that was welded to a martensitic stem. Both the intake and exhaust valves underwent a nitride surface treatment to prevent scuffing, with the exception of the tip and lock grooves.

Valve specifications for the 3.2L Pentastar V6 engine were as follows:

• Intake valve head diameter: 39 mm;
• Intake valve angle relative to the bore axis: 17 degrees;
• Exhaust valve head diameter: 30 mm;
• Exhaust valve angle relative to the bore axis: 18.8 degrees; and,
• Included valve angle: 35.8 degrees.

Intake

The 3.2L Pentastar V6 engine had a three-piece, composite intake manifold and a 74 mm throttle bore diameter. Instead of a mass airflow sensor, the Pentastar engine measured manifold absolute pressure (MAP), intake air temperature and oxygen, engine speed and valve timing – these inputs were then used in a speed-density algorithm to calculate the intake air volume.

Engine Start Stop (ESS)

From late 2014, the 3.2L Pentastar was available with Engine Stop-Start (ESS) which enabled it to shut down when the vehicle was stationary in traffic to reduce fuel consumption. The engine control module (ECM) monitored engine speed and, when the vehicle came to rest, cut fuel flow to the cylinders and turned off the engine. While the engine was shut down, the larger batteries maintained other vehicle systems – such as air conditioning – so that passenger comfort was maintained. Within 0.3 seconds of the brake pedal being released, the engine automatically restarted and the transmission was engaged. To minimise crank time, the ESS system had a high-speed/high-durability starter motor.

Injection and ignition

The 3.2L Pentastar V6 engine had electronically-controlled, sequential fuel injection via four-hole injectors that were mounted in the intake port (i.e. ‘port injection’). The engine had coil-on-plug ignition via long-life spark plugs that were positioned in tubes that were pressed into the cylinder heads and sealed in place. The firing order for the Pentastar V6 engine was 1-2-3-4-5-6.

The 3.2L Pentastar V6 engine had a compression ratio of 10.7:1 and two knock sensors were positioned between the cylinder banks in the engine’s ‘V’.

Lubrication and PCV

The 3.2L Pentastar V6 engine had a variable displacement oil pump which adjusted its flow rate and pressure to minimise energy use. Specifically, the pump operated in a low pressure mode at engine speeds below 3500 rpm and a high-pressure mode beyond that. A spring mechanism inside the oil pump adjusted the size of the pumping chambers to deliver the required oil flow. Furthermore, the oil-filter system for the 3.2L Pentastar V6 engine eliminated oil spills and contained an incinerable filter element for easier disposal than conventional oil filters.

The 3.2L Pentastar V6 engine had a positive crankcase ventilation (PCV) system which used a camshaft-mounted centrifuge to separate oil from crankcase blow-by gases.

Emissions control

For emissions control, the 3.2L Pentastar V6 engine had dual three-way catalytic converters and heated oxygen sensors; the Pentastar V6 engine did not have exhaust gas recirculation (EGR).