Tech minded aficionados will not be disappointed. The Eaton supercharger has 4 lobes with a high angle of twist which greatly boosts thermal efficiency over previous offerings. At rated power, the energy input required to drive the supercharger is just over 20 hp, which is quite good considering the unit is capable of blowing out over 1 ton of air per hour. Twin liquid-to-air intercoolers are housed under the supercharger within the intake manifold. Bosch's latest FSI system is employed boasting 150 bar of injection pressure. Direct gasoline injection allows a high static compression ratio of 10.3:1 to be possible without engine knock.
Further benefits are increased efficiency, power, and off boost response. The closed deck aluminum block (with etched Alusil bores) is very compact and lightweight (73 lbs). Audi has made their own proprietary modifications to the supercharger housing to improve NVH characteristics. The intake camshafts are equipped with a variable valve timing system. Audi's new Valvelift strategy is not employed, perhaps leaving the door open for future output expansion.
All the technology in the world doesn't matter unless the final product delivers what it promises. Admittedly, we were skeptical. We have grown to love the prodigious torque and effortless acceleration that Audi's turbocharged engines of the past are famous for.
My personal car is a biturbo B5 S4 warmed over to the tune of 500 hp, so it takes some muscle under the hood to impress me. Luckily, two days of blasting up and down the Spanish countryside have left me very impressed. Audi has done a great job with this powertrain!
The throttle response is at least as good as the outgoing V8, perhaps better. If you gingerly take the 3.0T up to about 3,000 RPM in first gear and mash the go pedal, you will be drop kicked in the sternum with an immediate surge that no turbocharged car will compete with. It responds NOW. Even the best turbocharged cars, especially at higher power levels, will need a few split seconds to build boost as the torque pours on like heavy molasses. Turbochargers have a delay, superchargers don't. The lack of a cliche supercharger whine will fool many people into thinking there is muted 5.0+ liter engine under the hood. Other than certain light throttle conditions at low revs, one would be hard pressed to identify it.
The near telepathic response is pretty amazing, and admittedly addicting. In what we consider a good decision, the behavior of this engine is not overly dulled electronically. While being refined in nature, it still has a slightly raw feeling to it when pushed hard. Turn off the ESP, and you can light up the tires on a hard 1-2 upshift, especially in the wet. The free revving nature is much quicker than the old 2.7T engine and on par with the RPM-happy V8's. The power delivery does not let up as you approach redline, but it doesn't build to a frantic crescendo like a highly strung normally aspirated car either.
There exists a certain segment of S4 fans who have bought into the platform solely for the V8 experience. Perhaps slightly superficial in their needs, the staccato V8 bark may be a make-or-break feature. For those who can try the car with a logical and open mind, the performance of the supercharged V6 is superior in every aspect...except for the soundtrack, which did leave us a little disappointed. In our opinion, the sound is slightly overmuffled, with an industrial Shop-Vac overtone at full kick. It lacks the authoritative bark of the V8, the mellow and smooth nature of the B5's biturbo V6, or the soul-stirring wail of the inline 5's of yore. Perhaps the aftermarket will find a way to uncork things a little.
On the plus side, S4's equipped with the new S-tronic 7-speed DSG box will be rewarded with playful cracks through the quad tailpipes on the lightning quick upshifts (ignition timing being retarded) or rev matching downshifts so perfect that any human short of the Stig would be unlikely to recreate them. Those 6-speed manual die-hards will be stuck with a less stimulating aural sensation, so you better pony up for the excellent Bang & Olufsen sound system.
When benchmarking other comparable engines, the 3.0T has raised the bar in this mid sized sports sedan segment. A glance at the spec sheet shows you this new engine is competitive; it sports 333 hp and 325 lb-ft of torque which easily puts it ahead of its closest competitor - the BMW 335i twin turbo. At a scant 189 kg (417 lbs), the 3.0T is lighter than the outgoing V8 (195 kg) and on par with the less powerful BMW twin turbo I6 (187 kg). For additional reference, the cast iron block 2.7T tips the scales at 200 kg. The 3.0T is also inches shorter than all three of those engines which is a huge benefit on a quattro equipped vehicle that still has an entire engine hanging forward of the front axle line. Audi promises the new engine will yield better performance and significantly improved fuel efficiency.
Initial engineering estimates predict 17 mpg city/27 mpg highway for the S-tronic 7-speed car, figures the V8 could maybe achieve coasting down the steep side of a mountain pass. With a tailwind. Electing to shift gears on your own will cost you about 1 additional mile per gallon on the highway. Chances are at least one of the S4 variants will be able to drop the gas guzzler tax.
The beefy torque curve and instant throttle response is well matched to either transmission choice. The B8 S4 is Audi's first vehicle to offer a true DSG S-tronic gearbox on a longitudinal vehicle platform (engine oriented North-South). There are 7 well spaced ratios for optimum acceleration, and the 7th gear is taller than the highest ratio found on the manual transmission netting slightly better highway fuel consumption. For those concerned about durability of this complicated gearbox behind a powerful engine, the rated torque capacity of the S-tronic is actually greater than that of the traditional 6-speed manual (369 lb-ft vs 332 lb-ft).
There is no type of "launch control" built into the S-tronic, so acceleration out of the hole isn't breathtaking. Launching above 2,000 RPM is out of the question. However, the shifts are performed blitzkrieg quick which will make up ground on manually shifted cars very expediently. Each new iteration of DSG we've driven is a significant improvement over the previous. We found the shift speed and shift logic of this unit a marked improvement over the TT's transverse DSG. The 6-speed manual is smooth and precise, lacking the rubbery feel of the 335i. We fully expect acceleration figures to be smack-dab between the outgoing B7 S4 and RS4 models. Despite Audi's conservative quoted figures, US magazines (who traditionally use 12" or 0.3 seconds of rollout) should be running about 4.7-4.8 second 0-60 times and dashing through the quarter mile at 13.4@105 mph if our Popometers are still calibrated to TUV specification. You heard it here first.
As good as the new engine is, don't take our gloating the wrong way. Audi's S cars have always been about more than a small car with a powerful engine. The overall package must be well rounded - a veritable decathlete if you will. Fortunately, the driving dynamics of the B8 platform are on par with the new engine - meaning, improved in every category.
Much like Porsche, the very basis of Audi's design concept does bring about dynamic compromises. Front engined cars with quattro still have the entire engine mounted fore of the front axle line creating a nose heavy car. Audi has spent decades taking this inherently flawed idea, and honing it to near perfection. In the past, this often meant that chassis behavior at the limit of adhesion was compromised to some extent. In most situations, factory stock Audis would tend to push or understeer at the limit. Although a safe and predictable response, this left many enthusiasts wanting more control over the rotation of the car at the limit of traction.
Beginning with the B7 RS4, quattro equipped cars started sending more torque to the rear axle than the front under normal conditions. Admittedly a step in the right direction, this was not a radical change in performance. Now Audi has a new technical solution, the "sport differential", which is capable of drastically changing the dynamic response of a nose heavy platform. Using innovative technology to overcome what was previously a shortcoming is what Audi's "Vorsprung duch Technik" tagline is all about.
Simply explained, Audi's quattro sport rear differential is ESP in reverse. A more generic term for this technology is torque vectoring. As we know, ESP (electronic stability control) combines wheel speed, steering angle, and yaw angle sensors to individually brake any of the 4 wheels on the car when a slip angle is detected. Those of us who have made that yellow triangle on the dash illuminate madly know the feeling all too well. Just as the car starts to slide, the electronic nanny steps in and straightens things out while scrubbing off speed. Somehow the same electronic widgetry deployed to harness your speed often manages to take the fun out of the equation at the same time. It's usually a little on the intrusive side. While a good feature for safety, it can easily become a hindrance on the race track or when enjoying an AWD car in slippery conditions. If you're one of those who tends to turn your ESP off as things start to get a little wild, you're a prime candidate for the sport rear differential option.
How does it work? The center section of the differential is surprisingly no different than a traditional open unit. On each outboard side, there is "superimposed gear stage" meaning an overdriven gear capable of turning either of the rear wheels 10% faster than the input speed. Each side has an electronically controlled clutch pack which can engage the "overdrive" gear. The clutch engagement is variable meaning either side can be sped up at any interval between 0 and 10%. This speed differential can send nearly all of the rear axle torque to one side, as long as both wheels are getting traction. The engagement of the differential clutches is dictated by the same sensors which control ESP operation (wheel speed, steering angle, yaw, etc). The behavior of the system can be further altered by the ADS (Audi Drive Select) mode.
End result, by speeding up individual rear wheels, this system can provoke the car to rotate in the same way ESP prevents the car from rotating. The system is active on acceleration and deceleration. Unlike ESP, the system can begin working before slip angle is detected, meaning the operational sensation is seamless and fluid. For an example on how the system would work, imagine negotiating a bend to the right. In this case, the sport differential can speed up the rear left wheel, causing the car to rotate and maintain a neutral cornering characteristic before understeer sets in. It can even induce and control oversteer!
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