The fun and spirited 2016 Audi S4 sport sedan is what happens when you inject an extra shot of performance into an ordinary Audi A4. That shot comes mainly in the form of a sublime supercharged V6 that pumps out 333 horsepower, about 50 percent more than the A4's four-cylinder. That V6 can be hooked up to an available dual-clutch automated manual. Not offered on the A4, it is remarkably quick-shifting and extracts the most of the car's performance. You also get a sport-tuned suspension for sharp, nimble handling and strong, upgraded brakes.

A unique grille, exclusive alloy wheels, subtle badging and distinctive trim accents set the 2016 Audi S4 apart from its A4 sibling.

But the S4 is much more than the sum of its sporting hardware. It also has a commendable ride quality, a well-appointed cabin with high-quality materials and even a relatively spacious backseat. This isn't a car that demands much compromise relative to its workaday A4 brethren. On the contrary, it's every bit as livable as an A4; it's just a lot more fun to drive when you feel like blowing off some steam on a curvy road.

If there's a downside here, it's that the S4's technology offerings are a bit outdated. The base Premium Plus trim doesn't include Bluetooth streaming audio, for instance, and its dash-mounted MMI controls aren't as user-friendly as the available console-mounted setup. To rectify both, you need to get the Technology package, which is a pricey option on Premium Plus and standard on the higher-level Prestige trim. One thing that can't be rectified is the lack of USB connectivity, as the S4 soldiers on for 2016 with Audi's proprietary digital media interface.

You won't find such problems on the 2016 BMW 340i, which also strikes a very appealing balance between performance and comfort. The same could be said of the luxurious and capable Mercedes-Benz C400 4Matic. If sharp handling is a priority, the Cadillac ATS should also be on your list. Even among this crowd, though, we think the 2016 Audi S4 remains a very appealing choice for a hopped-up entry-level luxury sport sedan.

The 2016 Audi S4 is a high-performance version of the A4 luxury sedan. It's offered in two trim levels: Premium Plus and Prestige.

The Premium Plus includes 18-inch wheels with summer performance tires, selectable drive modes (Audi Drive Select), a sunroof, automatic xenon headlights, foglights, LED running lights and taillights, automatic wipers, auto-dimming mirrors with exterior heating, keyless entry and ignition, tri-zone automatic climate control, heated eight-way power front sport seats (with four-way lumbar adjustment), driver memory settings, leather and simulated-suede upholstery, 60/40-split folding rear seatbacks, Bluetooth phone connectivity, the MMI infotainment system (with a dash-mounted controller and a 6.5-inch display screen) and a 10-speaker sound system with a CD player, an SD card slot, Audi's proprietary digital music interface (with an iPod cable) and satellite radio.

The Prestige package adds adaptive headlights and a Technology package that includes a 14-speaker Bang & Olufsen sound system, a color driver information center, a rearview camera, rear parking sensors, a blind-spot monitor, a navigation system, an upgraded version of MMI (with controls mounted on the center console and a 7-inch display), voice controls, Bluetooth audio connectivity, a CD player, HD radio and Audi Connect telematics.

The Technology package is also optionally available on the Premium Plus. Available exclusively on Prestige versions is the Driver Assistance package, which adds adaptive cruise control and adaptive steering.

Options on both Premium Plus and Prestige trims include a High Gloss Black package (19-inch dark gray wheels, gloss-black exterior trim and mirror housings in body-color paint instead of the standard silver), a torque-vectoring sport rear differential, adaptive dampers (with adjustable settings via Drive Select), premium leather upholstery and rear side airbags.

The 2016 Audi S4 is motivated by a supercharged 3.0-liter V6 engine rated at 333 hp and 325 pound-feet of torque. All-wheel drive and a six-speed manual transmission come standard, while a seven-speed automated manual (S tronic) is the self-shifting option. The available sport differential can enhance at-the-limit handling by distributing torque between the rear wheels in a matter of milliseconds to improve the car's cornering line.

With 333 horsepower, the S4's supercharged V6 delivers quick acceleration while remaining impressively smooth and refined.

In Edmunds performance testing, a manual-equipped S4 accelerated from zero to 60 mph in 4.9 seconds. That's an impressive time, though the 340i and C400 are similarly quick. An S4 with the automated manual bested that time with a decidedly swift 4.5-second run.

EPA-estimated fuel economy for the S4 is 20 mpg combined (17 city/26 highway) with the manual and 21 mpg combined (18/28) with S tronic. That's fairly frugal for a high-powered, supercharged V6.

The 2016 Audi S4 comes standard with antilock brakes, traction and stability control, hill start assist, front seat side airbags and side curtain airbags. Rear seat side airbags are optional. The Technology package (optional on the Premium Plus trim and standard on the Prestige) adds a rearview camera, rear parking sensors and a blind-spot monitor.

In Edmunds brake testing, an S4 with 19-inch wheels stopped from 60 mph in 106 feet, a strong showing for this type of sedan with summer tires.

In government crash testing, the S4 came up aces with an overall rating of five out of five stars, including five stars for both frontal and side impacts. The Insurance Institute for Highway Safety hasn't tested the S4, but it gave the related A4 its highest rating of "Good" in the moderate-overlap frontal-offset impact test but the lowest rating of "Poor" in the small-overlap frontal-offset test. The side-impact, roof-strength and seat/head restraint design (whiplash protection) tests all resulted in "Good" scores.

Audi's supercharged V6 engine is quite potent in the relatively compact 2016 S4 (and similar S5), generating relentless acceleration. It's also superbly refined, transmitting virtually no vibration to the cabin, even at redline. You'll get the best performance from the quick and smooth-shifting S tronic transmission, but if you don't mind shifting yourself, the traditional manual is a more involving choice.

In spirited driving, the S4's brakes inspire confidence without being grabby. Handling is nimble and precise. In addition, the optional sport differential noticeably enhances the car's at-the-limit handling by minimizing the understeer to which the nose-heavy, front-drive-based S4 is naturally prone. Thankfully, ride quality remains quite comfortable and the cabin is appropriately hushed at speed.

Audis are known for their stylish, sumptuously trimmed cabins, and the S4's interior doesn't disappoint. The quality of the materials is generally excellent, while the understated dashboard design should continue to look classy for years to come. Compared to the A4, the S4 adds form-fitting sport seats, a flat-bottomed steering wheel and gray-faced instruments, subtly signaling its sporting intentions without making a fuss about it. Drivers of all sizes should have no difficulty getting comfortable behind the wheel, while four adults can ride comfortably on long trips. That's not a given for sedans in this size class. Trunk capacity is average at 12.4 cubic feet.

Form-fitting sport seats and rich materials reflect the S4's sport-luxury character.

Infotainment features are controlled through the MMI infotainment system, which consists of a controller knob and related buttons that let you navigate through menus on a central screen. Overall, it's an effective system, though we've found BMW's iDrive and Mercedes' COMAND systems a bit more intuitive to use. Notably, in S4s without the Technology package, the MMI knob is located on the dashboard, potentially requiring an unwelcome reach from the driver seat to make adjustments. But when equipped with the Technology package -- as are most S4s -- the knob and buttons migrate to the center console between the seats, where they fall readily to hand and let you control an upgraded 7-inch display.