Is Audi TFSI More Than Just A Badge? It's Complicated

Audi has gone through some wacky phases with its naming conventions recently, and as more and more models use the same engine with different power outputs, it becomes even more difficult. It seems like every car nowadays is saddled with, say it with me, a turbocharged 2.0-liter inline-4. Most Audis saddled with the Volkswagen Group's ubiquitous 2.0-liter turbo engine are marked as 45 TFSI, but what all does that mean?

TFSI is an acronym that stands for Turbo Fuel Stratified Injection, and it was first used in the 2004 Audi A3. That humble A3 hid under its hood the world's first turbocharged direct injection gasoline engine, a technology that paved the way for all the ultra-high-output turbo engines that power many cars today. The TFSI name is reserved exclusively for Audi's gasoline-powered cars. Gasoline-electric hybrids are dubbed TFSI e, and diesels, which are no-longer sold in the U.S. after the Dieselgate dumpster fire, retain Volkswagen Group's TDI title in markets where they're sold.

Turbo Fuel Stratified Injection technology for gasoline engines was once a remarkable innovation that has since become quite commonplace. Traditional fuel-injected engines that don't use direct injection usually use throttle body injection or port injection; those systems spray gasoline into the intake port where it's mixed with air before it enters the cylinder via the intake valve. In contrast, gasoline direct injection directly injects gasoline into the cylinder, which increases efficiency by burning the fuel more completely which produces less exhaust. Gasoline direct injection requires beefed up injectors that can withstand high pressures and temperatures while still remaining incredibly precise for optimized fuel metering and atomization, as well as high-pressure fuel pumps, fuel rails, engine control modules, pressure sensors, and unique air intake systems to work properly. 

Direct injection is known to lead to carbon buildup on the intake valves and ports since fuel doesn't wash over them like it does in traditional port injection systems. This can be mitigated by using high-quality gasoline, and keeping up with maintenance like frequent oil changes and monitoring your spark plugs. The more advanced technology can also result in more expensive repairs, and it can push prices up. 

The benefits of direct injection, especially in turbocharged engines, outweigh the negatives. Direct injection is more efficient, allowing engines to use less fuel, and direct injecting a turbocharged engine means you get that boost in power while retaining more efficient combustion. This has allowed turbocharged direct injection engines to provide big power numbers while producing fewer emissions, which allows automakers to continue producing powerful cars despite stricter emissions regulations.

The numbers placed before TFSI don't actually mean anything outside the world of Audi's own numerical structure. Audi decided to make the numbers represent different ranges of power outputs. For example, 40 TFSI cars have power outputs that range between 167 and 201 horsepower. The ranges have changed a bit over the years too, just to make things harder to comprehend, and the brand is ditching the numbers for its next-gen vehicles completely.

This can be confusing in the case of the 2025 Audi Q3 45 TFSI. It is the only Audi model currently on sale with a 2.0-liter turbocharged inline-4 that produces 228 horsepower and 251 pound-feet of torque. All of Audi's other 45 TFSI models produce more power, but share the same 45 TFSI badge. The A4, A5, A6, Q5, and Q7 45 TFSI models all use a 2.0-liter inline-4 that produces 261 horsepower and 273 pound-feet of torque, so they make a lot more power than the Q3 45 TFSI, but the outputs are still in the same output range, as defined by Audi.

Engine displacement, aka the size of the engine, doesn't play a factor in the numerical aspect of the TFSI naming structure, just the engine's power output. That's what TFSI means, and the numbers that precede it mean, and no, I don't think the naming scheme makes much sense, either.