Audi S4 Reviews - Audi S4 Price, Photos, and Specs - Car and Driver
New Engine, New Transmission

To begin with, the S4 employs an all-new, 3.0-liter turbocharged V-6; internally called EA839, this engine is related to the 4.0-liter V-8 that Porsche will use in the next Panamera. Fitted with a BorgWarner twin-scroll turbocharger, the new mill makes 354 horsepower at 6400 rpm and produces 369 lb-ft of torque starting at a low 1370 rpm. That's 21 more horsepower and 44 more lb-ft of torque than was offered by the S4’s previous 3.0-liter supercharged V-6.

This engine mates to an eight-speed ZF torque-converter automatic, a unit that replaces the previous model's seven-speed dual-clutch automatic (DSG). The S4’s six-speed manual, previously standard equipment, also is dead. Really? Audi says it went for the conventional automatic because U.S. customers prefer the smooth torque-multiplication effect when taking off at a stoplight, something the dual-clutch gearbox is unable to provide.

https://www.autotrader.com/car-tech/2018-audi-s4-inside-the-new-engine-264821

The 2018 Audi S4 and 2018 Audi S5 have arrived. Based on the new generation of A4, they're the sportiest variants so far. Each one is a joy to drive, with sufficient power to exploit an excellent chassis and the traction that comes from all-wheel drive. The same engine propels both the sedan (S4) and coupe (S5) versions. It's a turbocharged 3.0-liter V6 developing 354 horsepower and 369 lb-ft of torque. Let's work off the premise that 250 hp is probably enough for most people who only drive on public roads and never on a track: overtaking power is sufficient, and steep hills will hardly register. That puts the new S4/S5 on the thrilling side of "just right."

Hardly surprising, since Audi's S cars have a sporty reputation to uphold. Let's take a closer look at the wonders of combustion.

Forcing the Issue

This is an all-new engine, even if the general idea is similar to that of the old S4. The previous generation used a supercharged 3.0-liter V6. Supercharging and turbocharging are forms of forced induction, where air is compressed before being fed into the cylinder along with that all-important squirt of gasoline. The result is a bigger bang -- a greater explosive force -- meaning more energy and ultimately making for a faster car. To all the people who say, "there's no replacement for displacement" (implying that big engines with many cylinders are superior), the smart reply would be, "forced induction means efficient production."

Superchargers are usually run off a belt driven by the engine, and turbochargers use exhaust gases to spin a turbine. In the past, turbos were plagued by "lag," where there was a discernible pause between the driver pressing the throttle pedal and the power coming in. During that lull, the turbine had to spool up before reaching its ideal working state. In a big engine, what happened next might be a sudden -- and scary -- burst of power. Superchargers don't have that issue, because the belt that drives them is turning all the time, so everything happens in a more progressive manner.
Volvo uses both methods of forced induction in some of its engines to eliminate even the slightest hint of turbo lag. Other manufacturers use what's known as twin-scroll turbochargers, which is what's happening here. It's a single unit but with two turbines, each with its own configuration. So one spools up super fast before the other kicks in. Add some advanced engine-management systems and turbo lag is defeated once again.

That said, it's still better to run at or comfortably above the level where the engine makes its maximum torque. In the new S4/S5's case, that happens at a really low 1,370 rpm. If there were a graph, it would stay fat and flat until 4,500 rpm. Between those engine speeds, throttle responses are immediate yet smooth.

The V of this engine sits at a 90-degree angle. Audi has situated the turbocharger between the two banks of cylinders, known as a "hot V" configuration. As well as offering effective packaging, it also means the compressed gases have the shortest route to travel, another safeguard against lag.

Although turbocharged car engines are more popular than ever thanks to advances in hardware and software, the idea of forced induction is not new. As far back as the late 19th century and into the early 20th century, engineers were trying various ideas and applying for patents. At high altitudes, naturally aspirated (non-forced induction) engines lose power, because the air gets thinner. That doesn't happen with a turbo or a supercharger, so it was only natural that aircraft engines were the first to benefit.


WTH Is TFSI?

Open the S4's hood and emblazoned on the plastic engine cover you'll see the letters TFSI. "T" stands for turbocharged, and the other bit means "fuel stratified injection." The important part here is "stratified." What happens is a fuel injector (there's one for every cylinder) delivers a precise amount of gasoline at precisely the right moment. The advantage is that less fuel needs to be used, with benefits in economy and emissions.
The pursuit of efficiency extends to adopting a method of internal combustion known as the Miller cycle. An American engineer, Ralph Miller, patented the idea in 1957, and it entails leaving the air/fuel intake valves open for slightly longer than during the widely used Otto cycle. The result is a two-stage compression phase. Audi says it has modified this cycle by using a centrally located fuel injector, variable-cam timing and what it calls "Audi Valvelift." Each cylinder has a pair of valves on the intake side and another pair on the exhaust side.

Worth the Weight

Generally speaking, weight is a problem for economy and performance alike. Enthusiasts always prefer a car whose weight is distributed as evenly as possible for a fine balance. The new S4/S5 engine has an aluminum head and block, making it about 30 pounds lighter than its predecessor, which helps make the steering feel a little more direct.
The main concern in this area is cylinder wear. Cast iron (used for engines over decades) is tough and, assuming the oil system works, can handle friction for hundreds of thousands of miles. Aluminum isn't quite so sturdy. Some manufacturers have used cylinder liners of basic cast iron, but that brings too much mass. Others have tried silicon-based sleeves, with varying degrees of success. In this case, the cylinder liners are made of lamellar-graphite cast iron 1.5 millimeters thick (about six one-hundredths of an inch).

Opus 2018

The 2018 Audi S4 and its coupe cousin have advantages of 21 hp and 44 lb-ft of torque over the outgoing models. They're capable of sprinting from a standstill to 60 mph in a rapid 4.4 seconds. Driving is never just about the numbers, though. The new S4 and S5 are both well-executed packages, with everything about them -- from power to agility to equipment -- tuned to perfection, like a world-class orchestra under a brilliant conductor. Think of this engine as the brass section.