Audi’s 4-cyl. DIG Powerhouse Hits Sweet Spot

Special Report

Story Behind 10 Best Engines

The Ward’s 10 Best Engines competition celebrates 13 years of recognizing outstanding powertrain development. In this seventh of a series, Ward’s chats with Audi engineers about the powerful, refined and technologically advanced FSI 2.0L 4-cyl. Watch for features on the other 2007 winners throughout the year.

Audi AG and parent company Volkswagen AG have collected 15 Ward’s 10 Best Engines awards in the competition’s 13 years, winning with everything from Volkswagen’s original TDI 1.9L 4-cyl. turbodiesel to Audi’s chesty 4.2L DOHC V-8.

But with the benefit of retrospection, none has been as well-rounded, as thoroughly right for the times as the FSI 2.0L turbocharged DOHC I-4, winner in 2006 and 2007 and now installed in a widening array of VW and Audi models.

Somehow, the VW Group’s engine developers always seem to be one step ahead of the market.

From the groundbreaking, refined TDI turbodiesel in 1997 (has it already been a decade for the TDI?) that augured the European tidal wave of new-age diesels to the seminal 5-valve 1.8T 4-cyl. – proof of how good downsizing can be when done right – VW powertrain development always seems to be ready with the best engine technology before anyone else.

Such is the case for the FSI 2.0L, the 4-cyl. follow-up to Audi’s FSI 3.2L DOHC V-6, the VW Group’s first direct-injection gasoline (DIG) engine offered in the U.S. in 2004 for ’05 models.

The FSI 3.2L V-6 is a magnificent premium-vehicle engine, but it was the ’06 availability of FSI (Fuel Straight Injection) technology in VW/Audi’s new 2.0L 4-cyl. that ushered today’s era of DIG fueling for “mainstream” engines. Audi says it is the first production engine to combine DIG with turbocharging.

2L FSI engine.

Audi engineers in Germany say the FSI 2.0L DOHC I-4 began a “predevelopment” phase as far back as 1999, with the aim to achieve series production in 2002-2004. The engine was adapted from the naturally aspirated FSI 4-cyl. engines that began production in 2002 in Europe.

Development goals for the FSI 2.0L 4-cyl. were threefold:

Given the engine has been a Ward’s 10 Best Engines winner in the first two years of its eligibility, it seems Audi’s developers succeeded on all fronts.

In terms of low-end torque and overall responsiveness, the FSI 2.0L has been lauded by Ward’s judges for its outstanding throttle response and infinitesimal amount of perceived turbocharger “lag.”

Audi’s engineers say this largely is a result of combined components that work in a highly complementary fashion. The on-paper result is a satisfying 200 hp at 5,100 rpm, ensuring the engine’s sporty nature.

But more important is the plump 207 lb.-ft. (281 Nm) of torque that peaks at just 1,800 rpm and hangs on all the way to 5,000 rpm, making the engine extremely tractable and seemingly much larger than its 1.984L.

BorgWarner Turbosystems tailored the variable-nozzle turbocharger’s performance characteristics specifically for this engine, says Audi, and the exhaust manifold’s design also suits the goal of integrating components and subassembies.

They also say the variable tumble flaps in the intake tract are crucial to optimizing the operation of the turbo, valving and other engine systems.

But the FSI fueling plays a major role.

Audi engineers say the unique characteristics of DIG are well suited for a forced-induction, downsized engine.

A3 offers 2L FSI as standard.

The FSI system, injecting fuel directly into the cylinder, allows for highly efficient combustion and a high compression ratio – higher than normally would be advisable for a turbocharged mill.

In the case of the FSI 2.0L, that value is 10.5:1, a value Audi says is “1 to 1.5 units” higher than might be possible without FSI. Higher compression ratios equate to higher thermal efficiency.

This all enables FSI engines to generate more low-rpm torque than the same engine with conventional port (indirect) fuel injection. This is particularly advantageous for small-displacement engines that rely on forced induction to improve torque.

“For a charged engine, the higher volumetric efficiency and the improved knock resistance also improve significantly the dynamic response of the turbocharger – (there is) reduced or almost no turbo lag,” Audi’s powertrain development team writes in response to questions from Ward’s.

“In addition, FSI is the enabler technology for using scavenging effects, which improve low-end torque and dynamic torque ‘build-up.’”

And while FSI helps to all but eradicate turbo lag – always the Holy Grail for small-displacement forced-induction engines – there are other happy results: a roughly 9% decrease in fuel consumption, engineers say, and a meaningful drop in emissions.

Audi says it will launch FSI engines late this year that emit at California’s ridiculously stringent Super Ultra-Low Emissions Vehicle (SULEV) level, while reduced fuel consumption was another goal achieved without much fuss.

The new FSI 2.0L DOHC I-4 is meaningfully more powerful – not to mention larger – than the port-injected 1.8T it ostensibly replaces, yet it enjoys better fuel economy.

Fuel-system suppliers played a giant role in FSI development, and Audi rattles off the list: Robert Bosch GmbH, Hitachi Ltd. and Siemens VDO for injectors; Bosch and Hitachi for the high-pressure fuel pumps.

Meanwhile, even today’s formidable 100 hp and 103 lb.-ft. (140 Nm) of torque per liter from the FSI 2.0L can be improved upon, Audi engineers say.

Fuel injection pressures could be increased to as much as 2,900 psi (200 bar) from today’s maximum of about 1,450 psi (100 bar).

The result, they say, could be power exceeding 134 hp/L and torque values in excess of 147 lb.-ft. (200 Nm) per liter – meaning today’s FSI turbocharged 2L 4-cyl. could bulk up to figures in the neighborhood of 268 hp and 294 lb.-ft. (400 Nm) of torque.

Audi already has variants of the engine in European “S” models that approach this output.

Those variants also employ a special aluminum engine block, abandoning the cast iron long favored by VW and Audi for its forced-induction 4-cyl. gasoline engines.

Audi engineers say the volume-production FSI engines will continue with iron blocks because “in terms of acoustic behavior, cast iron is much better.”

For small engines, they say the use of aluminum to save weight is less beneficial than with larger 6- and 8-cyl. units. They also like cast iron because it can more reliably and predictably accommodate higher boost levels.

Audi and other auto makers have suggested DIG fueling is the first phase of creating gasoline engines that mimic the characteristics of diesel, without the emissions liabilities of compression ignition.

The second phase would be future Homogenous Charge Compression Ignition, or HCCI; the design would marry spark-ignition and compression ignition in the same engine.

But Audi engineers say, don’t hold your breath – DIG is a technology that will be with us for a while.

“The homogenous charge compression ignition – or the Gasoline Compression Ignition (GCI ) – are topics in the research stadium and still far away from serial introduction,” Audi says.

“The controllability of the combustion with the worldwide deviations of fuel quality will be a major task. ‘Dynamic’ EGR regulation, (reliable) ignition without a spark plug and the combustion-noise problems have to be solved.”

For now, then, the company’s sticking with its multi-advantageous FSI technology, thank you.

Audi says all its U.S.-specification gasoline engines will boast FSI fueling by 2009. Worldwide, FSI will be featured on all Audi engines by 2011. This is something of a feat, considering the wide variability of fuel quality throughout the world.