Audi AG’s direct gasoline injection (DGI) system is the first volume-oriented application of the fuel-saving, power-enhancing direct-injection technology to be used in North America. It may be the start of something big.
We’re aware BMW, Rolls-Royce and even Isuzu already are in the U.S. market with DGI engines. None, really, are representative of the mainstream; only one, Isuzu’s DGI-wielding 3.5L DOHC V-6, is available in a vehicle that costs less than the $52,500 price cap for 10 Best Engines eligibility. It is Audi’s brilliant new FSI (Fuel Straight Injection) 3.2L DOHC V-6 that is positioned to put DGI technology on the map.
In a sense, DGI allows gasoline-engine engineers to impart some of the best attributes of diesels – higher efficiency, better torque output – to gasoline engines. Audi says FSI enables something on the order of a 10% boost in power and torque, yet affords an analogous boost in fuel economy.
Audi’s new 3.2L DOHC V-6 is first North American application of the auto maker’s FSI gasoline direct-injection technology.
The company of the Four Rings appears to speak the truth: Compared with Audi’s “old” 220-hp 3L DOHC V-6 (not direct-injected, of course), the new FSI 3.2L V-6 makes 35 more hp and 22 lb.-ft. (30 Nm) more torque. Yet despite the power and torque gains, the 3.2L FSI V-6 delivers 1 mpg better fuel economy in both city and highway driving.
Instead of injecting fuel into the intake manifold, where it is ingested with air when the intake valve opens, FSI injects fuel directly into the cylinder – at pressures that can exceed 1,160 psi (80 bar), 20 or 30 times the pressure used by conventional indirect injection. The higher pressures and the ability to precisely aim gasoline directly at the sparkplug largely are responsible for FSI’s power and efficiency gains.
FSI can be tuned exclusively to enhance fuel efficiency without sacrificing power by using a stratified-charge injection strategy in which there is an excess of air in the air/fuel mix. The stratified charge approach, however, produces an excess of oxides of nitrogen emissions, says Marc Trahan, director-product management and quality, Audi of America Inc.
Trahan says Audi chose, instead, for FSI to enable a standard “homogenous” air/fuel mixture that delivers meaningful power and torque improvements while managing a slight increase in fuel efficiency. Our only regret: The extra real estate required for the in-cylinder fuel injector means Audi has to ditch its novel 5-valve cylinder head architecture.
Ward’s testers were singularly impressed with the 3.2L FSI V-6’s driveability and throttle response. Better yet, the FSI V-6 weighs in with huge bursts of low- and midrange torque; the effect almost is that of a light-pressure turbocharger. Oh, and engineers win extra brownie points for managing a power-enhancing 12.5:1 compression ratio that can be satisfied with regular-grade unleaded gasoline.
With the FSI 3.2L DOHC V-6, Audi’s engine wizards prove high performance doesn’t have to come at the expense of reasonable fuel economy. Audi’s FSI is game-changing technology. So high is the company’s belief in FSI that it says all its gasoline engines will be so-equipped by 2006.
|FSI 3.2L DOHC V-6|
|Engine type||3.2L DOHC 90° V-6|
|Bore x stroke (mm)||84.5 x 92.8|
|Horsepower (SAE net)||255 @ 6,500 rpm|
|Torque||243 lb.-ft. (329 Nm) @ 3,250 rpm|
|Specific output||80 hp/L|
|Application tested||Audi A6|
|Fuel economy for tested vehicle (EPA city/highway mpg)||19/26|