In a discussion in the Allpar forums , the question was posed: Why are automakers moving away from V8 engines again?

At FCA US, the most powerful V8s are likely to continue for Ram and specialized Dodges, but the base 5.7 Hemi could be running on borrowed time. A turbocharged V6 can equal the Hemi’s power —  with twin turbos, beat it — and modern turbo engines can have flat torque curves than past ones.  Fast-shifting eight and nine speed automatics help, too.

Hemi engine with ZF HP8 8-speed transmission

All else considered, a turbo six generally gets somewhat higher fuel economy than a V8 (and therefore has lower pollution). The V6 is usually lighter than an equivalent V8; there are usually lower parasitic losses, with fewer moving parts.  The smaller size of the V6 allows for a smaller engine bay, which both helps with handling and cuts weight.

The engine bay size really comes into play with the next generation of rear-wheel-drive cars, being created by FCA for both Dodge and Alfa Romeo. They will share key dimensions and basic structures (including the engine bay), and to save weight and improve handling, they probably aren’t being designed with space for V8 engines.  Instead, the hottest ones will have twin turbo V6 engines — at Alfa Romeo, a Ferrari design.

The cost of the turbo hardware may or may not outweigh the extra two cylinders of a V8, but it's likely cheaper to design and produce one block, and to produce one family of engines than two. The 392 and 6.2 Hellcat can continue, since there’s no need to optimize their fuel use, given their much smaller sales; but moving to single and twin turbo V6 engines that produce more power than the current 5.7 Hemi would have definite benefits for FCA and drivers who just want the power, regardless of the engine form.