We've lifted off the gas pedal of the new 2013 Audi S8 sport sedan and something strange has happened.
A second before, there was a silken, bellowing, twin-turbocharged V8 engine propelling us down a back road behind Audi's Ingolstadt HQ and now there's, well, nothing.
The engine has gone quiet, a green bar grows across the bottom of the instrument cluster and, just like that, the all-new 4.0-liter V8 has turned itself into a V4. Not a buzzy and lifeless four-cylinder, but a perfectly smooth, sufficiently powerful stand-in for those times when you don't need 500-plus horsepower at your disposal.
Audi's All-New V8
It's clear that there is plenty going on below decks for the 2013 Audi S8's helmsman to consider, and it starts with Audi's all-new aluminum-silicon alloy V8. At 3,993cc, it's considerably smaller than both the standard 4.2-liter V8 in the A8 and the 5.2-liter V10 that was in the previous S8.
Although they would never admit it, Audi's engineers have taken a leaf out of BMW's book by mounting a pair of twin-scroll turbochargers inside the valley between the V8's cylinder heads. And like the BMW engine, Audi's 4.0-liter puts the inlet valves on the outside and the exhaust valves facing in. With a bore of 84.5mm and an 89mm stroke, the engine is slightly undersquare, although less so than the old 4.2.
Direct injection and variable valve timing and lift are also used, and the results are impressive. According to Audi, the 4.0-liter in the S8 generates 512 hp at 6,000 rpm and a crunching 479 pound-feet of torque between 1,750 and 5,000 rpm.
That's significantly more than the upcoming S6 and S7 sedans, both of which will use the same V8. Credit goes to a dual-branch air intake, more turbo pressure, a higher compression ratio, an extra oil cooler and changes to the valve timing, fuel injectors and crankshaft.
All that power will be put to good use, too, as the second application of this engine will be in next year's Bentley Continental GT. And you can only imagine what the lunatics at Quattro will do with it for RS models.
More Than Just Power
The new 4.0's real trick isn't more power, because that's pretty much a given in this day and age. The big news is how much more efficient the engine is compared to its predecessor.
By switching across to become a V4 when its headlining power and torque aren't required, the 2013 Audi S8's fuel consumption drops by nearly 15 percent. In the Bentley, a spokesman even talked of a 40 percent reduction in consumption and emissions. Then again, the Continental GT's standard engine is a 6.0-liter W12, so the switch to a 4.0-liter V8 is a much bigger step down.
Dropping four cylinders is accomplished by switching to a lumpless cam lobe, which closes both the exhaust and inlet valves on cylinders 2, 3, 5 and 8 and keeps them closed to run as a V4, then shuts down the ignition and direct injection as well.
The system only switches across to V4 mode in a tightly controlled set of parameters. The engine must be spinning between 960 and 3,500 rpm, the coolant must be at least 86 degrees and the gearbox must be in 3rd gear or higher. No one said getting good mileage was easy.
You Hardly Know It's Working
There's an indicator in the dash that changes color to green when the S8's running as a four-cylinder. Because V4 engines lack the inherent NVH qualities of a V8, Audi has fitted the S8 with both active engine mounts and Audi Noise Control in the cabin. Both systems work in a similar way, detecting unwanted vibrations and then using noise-cancelling technology to eradicate them.
When the driver needs more power, the sleeping cylinders fire back up within 300 milliseconds. During our brief drive of the new car, that 0.3-second switchover is pretty much lost in the eight-speed automatic transmission's kickdown anyway. We would venture to guess that without the lights on the dash, most owners probably wouldn't even know it was happening.
More Than Just an Engine
There's more to the 2013 Audi S8 than sheer power, however, so Audi tweaked the suspension to complement the new V8. An adaptive air suspension is standard and it rides nearly half an inch lower than the A8. Call up the more aggressive modes and it will drop another half inch. Audi's dynamic variable steering is also standard, so the ratio can be adjusted by as much as 100 percent depending on how aggressively you dial up the Audi Drive Select settings.
Of course, more capable brakes are part of the package, too. Up front, the vented and perforated discs measure 15.8 inches in diameter while the rears are just over 14 inches across. Six-piston calipers are mounted on the front discs, with single-piston calipers on the rear discs. If you want to shave 28 pounds off the brake setup, there's a set of carbon-ceramic discs available as an option.
There's plenty of room for the brakes, too, as the standard wheels are 20-inchers with 265/40R20 tires at each corner. Optional 21-inch wheels and tires are also available.
Is Smaller Better?
Like so many of its competitors, Audi has chosen to embrace smaller-displacement engines to increase fuel efficiency and reduce emissions. It's a logical progression, especially now that modern turbochargers help make up for the lack of size, with fewer ill effects on the power delivery.
We didn't get enough seat time to feel the full wrath of the new engine's power, but the refinement of its fuel-saving measures was certainly on display. To some that might seem like a sad indication of where performance sedans are headed. Don't worry, though. The 2013 Audi S8 remains on solid performance ground; it's just a little smarter about how it got there.
Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report
