Nissan Motor Co. Ltd. formally announces two new versions of its legendary VQ V-6 gasoline engine.

Displacing 3.5L and 2.5L, the new VQ35HR and VQ25HR are designed for front-engine, rear-wheel-drive applications and feature more power and improved emissions over current VQ mills, the Japanese auto maker says.

The HR designation stands for “high revolution” and “high response,” Nissan says, adding the engines feature a smooth powerband with a class-leading 7,500-rpm maximum engine speed.

Horsepower and torque figures have not been officially released, but reports have the new 3.5L mill pumping out 306 Society of Automotive Engineers-certified horsepower.

Benefits of the redesign include a 10% improvement in fuel efficiency compared with current VQ engines, along with a Super Ultra-Low Emission Vehicle (SULEV) rating, the auto maker says.

A redesigned engine block with improved rigidity, along with the adoption of continuously variable intake valve timing and electromagnetic exhaust valve timing, are the most significant editions to the HR engines.

Other improvements include: lighter, redesigned internal components; symmetrical intake system; isometric exhaust manifold with symmetrical exhaust system; and improved ignition and emission electronics.

Nissan says it will build the engines at its plant in Iwaki, Japan.

The all-new ’07 Nissan Skyline, which launches in Japan this fall and is known as the Infiniti G35 in the U.S., will be the first application for the new engines. The redesigned ’07 G35 will feature the new 3.5L VQ powerplant, as well, when it goes on sale in November.

Nissan has produced more than 5.5 million VQ V-6 engines since its introduction in 1994. The engine also is the only powerplant to appear on Ward’s 10 Best Engines list every year since the competition’s inception in 1995.

msutton@wardsauto.com