The changes will debut in the 2016 Jeep Grand Cherokee, and make for fuel economy improvements of more than 6%. Torque has also increased more than 14.9% at engine speeds below 3,000rpm, depending on the application.
What are the changes?
The headline change is the introduction of two-step variable valve lift (VVL), which benefits fuel economy and refinement. Cooled EGR delivers greater efficiency and enables knock-free operation at higher loads, and the VVT system has been upgraded too. Other changes include a new intake manifold (which alone increases power from 294ps to 299ps), an increased compression ratio (11.3:1), high-tumble intake ports and shrouded combustion chambers and eight-hole fuel injectors with optimized atomization.
How has Chrysler achieved the large drop in fuel consumption?
Chrysler says it’s a detailed effort, no improvement was too small to chase, but the engineering team had to find the combination of features to deliver the greatest benefits over the widest operating range.
FCA says its two-step VVL is the most significant change. The system is designed to remain mostly in low-lift mode until the customer demands more power; then it responds by switching to high-lift mode for improved combustion.
The result is less overall pumping work, which on its own, accounts for a fuel-economy improvement of up to 2.7%, compared with the 3.6-liter engine’s previous iteration. The addition of cooled EGR benefits emissions reduction and further cuts pumping losses and enables knock-free operation at higher, real-world loads. This translates to a fuel-economy improvement, on its own, of up to 0.8%.
The engine’s upgraded VVT system further aims to reduce pumping losses. The new unit moves to torque-driven cam-phasing, which reduces oil demand, and the new VVT system also increases its range of authority to 70°, from 50°. This helps mitigate knock during hot starts and expands the operating range of the stop/start system, which is driven by a high-speed/high-durability starter that reduces crank time for quicker restarts.
More than that, FCA engineers say that they’ve put 7.6m customer-equivalent kilometers on the revised engine, using computer simulation and physical tests.
What have the engineers done to reduce friction?
FCA has used a number of friction reduction strategies that contribute to an additional 1% improvement in fuel economy compared with the outgoing engine. Particularly notable is the use of HG-R1 on the timing drive guide-faces. The new Pentastar is the first production engine to feature this low-friction material. Also contributing to friction reduction are new valve springs, low-tension piston rings and piston pins which feature diamond-like carbon coating.
What about cutting weight?
Despite the many changes to its 3.6-liter Pentastar engine, Fiat Chrysler is pleased that the engine weighs in at around 148kg, depending on the application 1.8kg less than the old Pentastar, despite the addition of new content weighing 5.9kg.
To achieve the reduction, FCA says that a thin-wall strategy was used to reduce the nominal thickness of certain die-cast components, without compromising NVH.
Windage-tray weight was cut by 19% and front-cover weight by 5%. Two-piece oil pans were eliminated too, with the exception of trail-rated vehicles. The engine’s crankshaft also went on a diet. Its main bearings and pins were trimmed, which contributed to an overall block-assembly weight reduction of 2.7kg.
September 9, 2015