Last Summer, 80 drivers came together at Mandarin Hotel in Washington DC to take part in Audi’s TDI Efficiency Drive Challenge. Among the drivers were journalists, scientists, startup entrepreneurs, bloggers, policy makers, and three Audi Club members: Paul Rivera (Southern CA), Matthew Welch (Lone Star), and myself (Golden Gate).

The drivers were split into four groups and our arrival and departure were staggered. Everyone arrived the night before the competition day for technical presentation and panel discussion followed by dinner. The next morning, each group was tasked to drive three cars in three segments: Q5 TDI, A6 TDI, and A7 TDI on predetermined routes. The drivers in each car took turns at midpoint of each segment. Our driving stats were collected by a special add-on device installed on each car. At the end of each day, the winning team with the highest miles per gallon was announced at dinner.

TDI History at a Glance
Audi brought the very first TDI into production in 1989. It was based on its proven 2.5L five-cylinder design. Then in 2006, Audi introduced a slightly bigger 3.0L V6 TDI. The second TDI generation produced more power and boasted better fuel efficiency. It achieved Tier II/Bin 5 ULEV CARB through the use of a DeNOx catalytic converter and the aid of AdBlue after exhaust treatment.

What do all of these acronyms mean? Two tiers of emission standards for light-duty vehicles were defined as a result of the Clean Air Act Amendments of 1990. Tier 1 was in effect between 1994 and 1997. Subsequently, Tier II took effect starting from 2004 to 2009. Bin 1 to 10 is a sub-ranking within Tier II. Bin 1 is designated for the cleanest vehicle with zero emission and bin 10 is designated for the most pollutant vehicle. ULEV stands for Ultra-low emission vehicle, and CARB stands for California Air Resource Board.

These standards define multilevel emissions restrictions for carbon monoxide, oxides of nitrogen, particulate matter, formaldehyde, and non-methane hydrocarbons. In short, to you and me, these standards improve the air quality we breathe every day.

In 2013, the second version of the 3.0L V6 TDI was introduced. It met ULEV2 certification, which has much more stringent restrictions for the pollutants than ULEV1. 2014 A8, A6, A7, Q5, and Q7 get this enhanced clean diesel engine. Not surprisingly, the advanced diesel technologies that go into this latest TDI came from Audi Motorsports experiences and achievements. Audi won total of eight 24-hours Le Mans races with TDI; six with TDI Clean Diesel and two with diesel hybrid R18 LMP1 car.

The new 3.0 V6 TDI
Audi engineers started with the following goals in mind to improve the first version of 3.0L V6 TDI: compact innovative engine design, lightweight, ULEV2 emission standard, improved performance and refinement, and excellent fuel economy. They achieved all of the above and then some. Using many weight reduction techniques and innovative component designs, weight was shaved from crankcase, crankshaft, main bearing frame, upper oil pan, chains, exhaust manifold, turbocharger, and cylinder head. This new and compact engine is now weight 55 lbs less than the previous one.

The innovative engine design helps reduce fuel consumption at higher speeds. Piezo injectors lower the combustion noise that most people dislike on diesel engines. It also optimizes the distribution and timing of fuel injected into the combustion chamber, helping to reduce emission further. Then, diesel particulate filters reduce up to 95% of diesel particle emissions. Next, AdBule diesel exhaust-treatment that helps turn NOx emissions into harmless nitrogen and oxygen is applied. All of these techniques enable this new TDI to meet ULEV2 emission standard.

On the performance side, this new 3.0L V6 TDI produces high engine power output of 240 hp and 428 lb-ft torque at amazingly low 1,750 rpm. The variable turbine geometry in the new TDI clean diesel engine builds torque smoothly and without delay, even at very low speed engine, maximizing driving dynamics. This marvel catapults A6 and A7 luxury sedans from 0 to 60 mph in only 5.5 seconds! Q5 and Q7 go from 0 to 60 mph in 6.5 seconds and 7.7 seconds respectively. A8 TDI does it in 6.4 seconds.

Here comes the nice surprise. Despite such exciting performance figures, these TDI cars are fuel sippers. 2014 Audi A8L TDI is the best fuel economy car in its segment, including gas, diesel, and hybrids—24 mpg city, 36 mpg hwy, 28 mpg combined—providing up to an 857 mile range. A6 and A7 TDI both have 24 mpg city, 38 mpg hwy, 29 mpg combined, providing up to a 733 mile range. Q5 TDI has 24 mpg city, 31 mpg hwy, 27 mpg combined, providing up to a 614 mile range. This allows Q5 TDI owners go to the pump less than other SUV drivers in its segment.

In practical terms those numbers mean the following. You can go from New York City to Chicago in a single tank of fuel in A8L TDI. You can go from San Francisco to San Diego in a single tank of fuel in Q5 TDI and still have plenty of fuel to do sightseeing in the city. And you can go from Chicago to Washington DC in a single tank of fuel in the high performance luxury A6 or A7.

Our TDI Experience
Our first car to drive was Q5 TDI S-line. The first thing we noticed was the unexpected sound of the engine when it was cold and idling. It was very smooth and quiet. On the highway, we opened up the car a bit. This clean diesel engine had a very sporty race-bred sound. Having 428 lb-ft at amazingly low 1,750 rpm was a brand new experience for both of us. When we drove very lightly, the acceleration was very smooth and predictable. But when we drove it spiritedly, we could feel our organs pressed against the sporty leather ventilated seats. It was that amazing!

Matthew and I decided that we would have a go in trying to win the challenge. The challenge was to obtain the highest combined mpg for the day driving three different cars: Q5, A7, and A6. So, we drove gingerly for the rest of the trip. We were doubtful about winning it because when we looked at the leader board from the previous days, the winners were able to obtain more than EPA highway mpg numbers. We knew that the routes were only less than 20% freeway. The average top speed was only just below 40 mph. So, how could they achieve higher than a highway EPA mpg number?

The weather was on our side. It drizzled on and off throughout the day and the temperature was never above 80. So, we had an advantage over the other groups because earlier that week the temperature had been so hot that everyone had cranked up their air conditioning. We used the fresh air mode all day long and kept the fan speed at the minimum to reduce the electricity consumption, hence the alternator did not work as hard.

After exiting the highway, the road became narrow and twisty. Routes had been pre-programmed into our navigation system. We passed countless beautiful pastures with rolling hills. Many stretches of the roads had canopy trees. At the top of the hills we could see many hills interlacing each other towards the horizon.

Matthew and I discussed other techniques to minimize fuel consumption. We decided to apply the lesson in physics about potential and kinetic energies. At the top of the hills, we pushed the throttle gingerly and we never revved beyond 2000 rpm, to gain decent downhill speed such that we had enough kinetic energy to push the car up the next hill without using much help from the engine. When driving downhill with decent momentum, we placed the gear in neutral so the engine speed went below 1000 rpm, hence it reduced further fuel consumption.

The Quattro and Dynamic-mode suspension enabled us to carve corners and switchbacks very confidently even while we were coasting downhill. We didn't get the best mpg in our first leg in the Q5 as we experimented with our driving techniques. And at one point, while I was in the passenger seat and was so mesmerized by the scenery, I kept the window down for half an hour to take pictures. That didn't help fuel consumption because the car aerodynamics was not as good as it could be.

We turned on the Start-and-Stop feature which turns the engine off when the car came to a complete stop. As soon as the pressure on the brake pedal is released, the engine starts as it anticipates the next move. This feature improves fuel efficiency in stop-and-go traffic around town.

Lunch time was filled with conversations from drivers about their exciting experience with clean diesel. Many had never driven a diesel engine, so they walked into the lunch room with ear-to-ear smiles. Others didn't care so much about the TDI efficiency drive challenge. After they had experienced the monster under the hood, they succumbed to their temptation; driving the car in the most spirited way possible through hairpins, switchbacks, zigzags with elevation changes. Matthew and I were envious of this hair-raising group but kept reminding ourselves that we came here for a different reason.

The A7 lived up to its expectation as a luxury smart executive car. The award winning exterior is matched by the sublime interior. Tactile feel is perfect. Buttons and dials feel consistent allowing our brains to develop muscle memory quickly. The extraordinary craftsmanship of Audi engineers creates an unparalleled comfortable feeling; like when we put on our worn-but-favorite gloves. After a few minutes driving it, Matthew claimed A7 to be the car for him.

We chose Individual Setting for Audi Drive Select, instead of choosing from Auto, Dynamic, or Comfort. In the Individual setting mode, Suspension, Steering, Engine, and Transmission can be set separately. We selected Dynamic-mode for Suspension and Steering, and Comfort-mode for Engine and Transmission to prevent ourselves punching the accelerator and awakening the ferocious monster under the hood.

We were nervous when we reached the midpoint of this stage because the A7 computer showed our average mpg was only 29. Had we driven the car so badly? But then we saw the elevation figure at the bottom right of the satellite navigation. It was close to 600 ft above sea level. We smiled. We had plenty of coasting to do on the way down.

In late afternoon, it was time to buckle up in the A6. The car felt smaller than its bigger brother A7. We configured the Audi Drive Select in the same way as the A7.  However, even though the setup was the same, the A6 ride felt stiffer and the steering darted more. The engine growl was louder. Overall, A6 felt more on the aggressive side than the well composed A7. A6 was my favorite car of the day because it gave me a bit more naughty feeling.

It was late afternoon and we had been driving for over six hours but  were not tired. The low end torque on clean diesel made these cars effortless to drive. We didn't drive the cars spiritedly like the hair-raising group, but enjoyed the rhythm we created for fuel efficiency very much.

We arrived back at the Mandarin hotel just before 6 pm. According to the Audi engineers who were responsible for inspecting the cars and downloading and tabulating the data, we were the last car to come back. The group dinner was at a  restaurant where conversation flowed about the day’s driving adventures. We thanked Audi for inviting us to participate in this great event, but more importantly, for bringing the best diesel engine in the world. Matthew and I now have TDI on our shopping list. Oh, yes, we unexpectedly won the competition, not only for the day but for the overall title with the best combined fuel efficiency of 38.7 mpg and the second highest average speed of 38.4 mph!