Legislators intent on requiring new light vehicles to consume less fuel and emit fewer pollutants are forever altering the American automotive landscape by demanding smaller engines.

Some enthusiasts argue this change is for the worse, but it’s not. Set the bar high enough, and some auto makers, such as Fuji Heavy Industries, will clear it in clever ways.

The purveyor of the Subaru brand earns its third Ward’s 10 Best Engines trophy, this time for its latest high-output boxer engine. This 2.0L 4-cyl. naturally aspirated gem produces 100 hp/L and instills hope that cars of the future will not be appliances, void of passion and emotion.

Subaru’s “FA” boxer finds a pleasant home under the hood of a new rear-wheel-drive 2+2 coupe that is a collaboration in every sense of the word: the Subaru BRZ and its twin, the Scion FR-S.

Subaru needed Toyota to help create the ideal, lightweight package to showcase this engine as much as Toyota needed Subaru’s expertise in designing and building a power-dense engine that could sit unusually low and toward the center of the chassis to enable darty handling and rail-like cornering.

Toyota should not be overlooked for its own contributions to the FA engine, which bears the names of both vehicle brands on the intake manifold.

Toyota gets an assist developing the fueling system that integrates both direct and conventional port injection.

Spraying fuel directly into the combustion chamber creates a cooling effect and enables a high 12.5:1 compression ratio to extract maximum energy from the fuel. In light- and medium-load conditions, Subaru says the port fuel injectors help produce precise combustion and boost efficiency.

This same belt-and-suspenders approach is used in the Lexus IS 350’s 3.5L V-6, which won four consecutive Ward’s 10 Best Engines trophies through 2009.

The 2.0L FA boxer is more compact (and considerably more powerful) than Subaru’s 2.0L FB boxer in the Impreza sedan, with a shorter intake manifold and shallower oil pan.

The bore and stroke dimensions are identical (86 mm) in this truly “square” engine architecture, and 4-2-1 exhaust routing has been tuned for a throaty sound while intake pulsations are piped directly into the cabin via the footwell.

Disgruntled bloggers say the FA boxer isn’t so special, not when Honda was producing 120 hp/L with the S2000 roadster’s naturally aspirated 2.0L (also a 2-time Ward’s 10 Best Engines winner) more than a decade ago.

In truth, both engines are thin on torque, but the S2000, with its 8,900-rpm redline, required considerably more caning – and earplugs. Unlike the S2000, the BRZ and FR-S are fine daily drivers.

We hammered the BRZ and still managed nearly 29 mpg (8.1 L/100 km) with the 6-speed manual and 27 mpg (8.7 L/100 km) with the 6-speed automatic. Pummeling the S2000 for 10 Best Engines in 1999, we didn’t even pay attention to fuel economy.

There’s nothing wrong with waxing nostalgic about bygone cars, but that was then and this is now. Honda stopped producing the S2000 three years ago, and it also was more expensive than the BRZ/FR-S.

A viable competitor in the U.S. for Subaru’s FA is the 2.0L (likewise naturally aspirated) in the Mazda MX-5 Miata. But the FA trounces it by 33 hp and makes more torque.

A turbocharged version of the FA engine first appears in 2013 in the Forester cross/utility vehicle, which will be a Ward’s 10 Best Engines contender in the fall.

Together, Toyota and Subaru maximized their resources to demonstrate that cars of the future, using the finest powertrain technologies available, can be lightweight, fuel-efficient, affordable and thrilling to drive.

tmurphy@wardsauto.com