An unmistakable trend emerged as WardsAuto editors cycled through 36 vehicles during evaluations for the 2012 Ward’s 10 Best Engines competition: Engines are getting smaller.

Not only are 4-cyl. engines ubiquitous and a lot more enjoyable to drive, they also are gravitating toward a universal displacement of 2.0L.

Yes, there are new 1.6L and 1.8L I-4s, but eight of 34 engines evaluated for 2012 displace 2.0L and four of them made this year’s list. Of all the trophies awarded over the course of 18 years of Ward’s 10 Best Engines, never before have that many engines of the same size made the cut.

The reasons for the convergence at 2.0L differ from auto maker to auto maker, but tax incentives in Europe and China make it worthwhile to stay under 2.0L. And auto makers have discovered 2.0L as the sweet spot for both power density and refinement.

Besides, an engine size that starts with “2” is psychologically more marketable than if it starts with “1” and is nearly as fuel-efficient.

This year’s 2.0L superstars – all of them new or significantly upgraded – hail from BMW, Ford, General Motors and Mazda. All use direct-injection, and three of them are turbocharged.

All four are among the most-sophisticated engines offered by their respective brands, and yet they are affordable, practical and efficient.

And all four powerplants arrive in a displacement that soon will be as common as black in a Model T showroom.

Filling out the 2012 list are four repeat winners from Audi (3.0L supercharged V-6), BMW (3.0L turbo I-6), Chrysler (3.6L V-6) and Ford (5.0L V-8), as well as two first-timers from Hyundai (1.6L I-4) and Nissan (3.5L V-6 hybrid).

To be eligible for the competition, engines must be all-new or improved and available in a regular-production, U.S.-specification model during first-quarter 2012. Vehicle base price is capped at $55,000.

WardsAutoeditors drive the vehicles in their routine commutes during October and November and score each based on power, technology, refinement and observed fuel economy.

The awards will be presented Jan. 11 at a ceremony during the North American International Auto Show in Detroit.

This year’s winners automatically are eligible for the 2013 competition.

tmurphy@wardsauto.com