A new, smaller V-8 engine with cylinder-deactivation technology is at the heart of three new S models Audi will unveil at the Frankfurt auto show next month.

Blending performance with fuel economy, the 4.0L twin-turbo V-8 develops 420 hp and peak torque of 406 lb.-ft. (550 Nm) across a wide band of 1,400 to 5,300 rpm and can take the new S6 model 0-62 mph (100 km/h) in a scant 4.8 seconds. Top speed is electronically limited to 155 mph (250 km/h).

But representing a downsizing from the 5.2L V-10 offered in the previous-gen model, the 4.0L achieves 24.3 mpg (9.7 L/100 km) in the rear-drive S6 and 24.0 mpg (9.8 L/100 km) in the all-wheel-drive Avant model, a 25% improvement.

Audi employs cylinder-deactivation technology for the first time in the new engine and adds a stop/start system to prevent the engine from burning more fuel.

The cylinder-management system deactivates four cylinders under partial loads, while active noise cancellation technology kicks in to counter any additional unwanted sound entering the cabin.

Low-frequency vibrations in the engine are countered via electronically controlled engine bearings.

The engine is mated to a 7-speed automatic transmission in the S6 and S7.

The new S7 gets the identical engine, but output is boosted in the S8 model to 520 hp and 479 lb.-ft. (650 Nm) of torque at 1,700-5,500 rpm, good enough to take the flagship car from standstill to 62 mph in an even quicker 4.2 seconds.

Fuel economy in the S8, equipped with an 8-speed tiptronic transmission, is pegged at 23.1 mpg (10.2 L/100 km), a 23% gain from the 17.8 mpg (13.2 L/100 km) average for the previous-generation car equipped with the 5.2L V-10.

All three S models feature upgraded interiors and a elongated list of standard equipment. They’ll arrive in showrooms in spring 2012.