audi40

My sentiments exactly, and I had a 3.0T previously.

audi40

Audi rates the A6 3.0t @ 5.3 secs compared to 5.5 for the TDI. C&D hasn't instrument tested an A6 tdii, but did record a 5.8 second 0-60 in a heavier and less aerodynamic Q5 TDI.

feralc

I am sorry but the diesel engines DO NOT perform as a gas engine, they have more power hauling but not accelerating (from standing still, 40-65mph, top speed, you name it), they don't rev that high, they don't sound as nice, etc.
They fit a specific purpose in drivers like yourselves that do not fit it in mine,
You love your Diesel engines and that is perfect but as I said in my book is not worth the trade off, and I believe any S/RS owner would agree with me.
You took the "lack of performance" too personal I should have said the "difference in performance"

perlfather

The Audi USA website shows for the A7 a 0 to 60mph time of 5.5 sec for the TDI and 5.4 s for the TFSI. Thus I calculated a difference of 0.1s.
I looked at the A6 page and noticed they quote 5.5 and 5.3 respectively.

in2dwww

Correct. But the logic here for us diesel owners is that there is no trade off. It's just a different power delivery and different marginal utility. High revs are not where the money's at. It's down low, which gives the off-the-line utility in situations like city driving, highway passing, and quiet cruising. For instance, at 55mph, the engine is turning over at 1150rpm. At that engine speed, relative to wind and road noise, you don't hear anything. Yet, the engine is sitting right at the sweet spot for the torque curve, meaning you can reach 70mph rapidly and with little drama. That's the difference, subtle, but major for a lot of us.

Again, the supercharged V6 is excellent. For the application, I like that they've turned the A6 into a bad-*** long hauler. Range per tank is where the TDI can beat out any other A6 in the lineup. If you happen to have a need for long range, give the TDI a shot.

perlfather

Exactly correct the 2nd time - "a difference in performance" is more appropriate and correct.

I think you are making a mistake in thinking that hp equates to acceleration. Torque is more important to acceleration. An engine's power affects acceleration, however it affects strongly top speed and acceleration near the top of the allowable RPM range. TDI engines have poor top end hp (240) which affects acceleration above about 100mph but have high torque at low RPM which is why they do well in 0-60 and especially in accelerations where you are between about 1500 and 2500 RPM (428 ft/lb).

I have often driven diesels as rental cars in Europe and over the years found them ever more satisfying and closer in performance to gasoline engines. This is my first diesel engine and i think it really suites our driving in the US.
We in US/Canada are all quite fortunate to drive such great cars and be able and purchase them for less money than people in virtually any other country in the world. (big difference in price between us and the EU)

Needless to say a TDI will not appeal to the S and RS people. Nor will it appeal to those that keep RPMs consistently above 5500 RPM or those obsessed with how to lower the car by 2.7189mm etc.

in2dwww

Those numbers can be achieved with higher cetane fuel. In Europe, the diesel is 50 cetane while in the US, it's commonplace to find 40 cetane. The min cetane for the US is 35. You can use an additive (PowerService) to boost cetane by 8.

in2dwww

Torque does all the hard work of acceleration but the HP needs to sustain the speed and fight wind resistance. I know first-hand from a Jetta TDI with manual transmission. The Jetta manual was fun because it was a manual diesel. I never had to downshift on the highway... just keep it in 6th and put the foot down. But since it only had 120hp, it was hard to get past 80. I had to downshift and redline to reach the hp and got it up to 105. 105 was not vmax, but I wasn't going to push it. The Jetta is not aerodynamic, and above 80mph, the 120 hp is at the top of the rev range. If they find a way to get more hp from a diesel at redline and if they make slippery, lighter cars, then diesels might have a chance at s/rs or amg or m status.

feralc

Guys sorry if I offended you
That was not my intention at all
The only reference I have with TDI is a Q7 I drove side by side with a Q7 prestige, because My wife's cayenne turbo gas consumption makes me cry everytime I put more than 100 Dlls for 250 miles of range. So for that specific reason I wanted to test drive the TDI engine but I did like more the gas engine version if the Q7, and because I already have that engine in my A7 I knew all the sweet things I could do with it.
In the A7 forum I wrote the following in a thread and I still believe the 240hp TDI should not be more expensive than the TFSI, if we were comparing a bi turbo version then (maybe) I would be thinking differently.


"I do not understand why
1 Audi does not offer the bi turbo version with 313ps (308hp) in the United States
2 the pricing of the 240hp diesel is more than the gas version (starting at 69,800usd for the diesel and 67400usd for the gas)
In the UK the 245ps (240hp) is at the same price level than the gas version (53,250 gbp for the gas and 53,150 for the diesel) and the most expensive of the line is indeed the bi turbo version at 56,795 pounds.

I am just comparing the difference between the models of course the cars in the UK are way more expensive in dollar terms.
And I believe in Norway they are in 6 digits territory."

mirin S6

Not true. Here is a relevant response from a physics forum.

People often confuse power and torque because car enthusiasts tend to (unknowingly) use these words for different concepts. This is a physics site, so I'm going to go ahead and use the definitions from physics.

The full-throttle behavior of an engine can be approximately modelled as a device which has some function τ(ω) associated with it. This fixes the torque it can produce as a function of engine speed (rpm). This function is not at all constant, although engineers often strive to make it as flat as possible.

Regardless, given the torque function, there is an associated power P(ω)=ωτ(ω). So if the torque is known at all speeds, the power is known at all speeds (and vice versa). You can't have one without the other.

Despite this, it is common practice for engines to be advertised only in terms of their peak torque and peak power. The engine speeds where those conditions may be found are also usually given. The peak power is very important for reasons I'll get to later, but the peak torque is essentially useless all by itself. The reason is that the gearbox can multiply the torque to (essentially) any amount whatsoever at an appropriate speed. But an ideal gearbox cannot change the power.

Staying with the ideal case, the maximum forward force that a car can produce is entirely determined by the power its engine is producing and the car's overall speed. So fixing speed, maximum acceleration is always reached by maximizing the engine's power output. It is the job of the transmission (and driver) to use the gearbox to keep the revs as close to the engine's power peak as possible if full acceleration is desired.

Modern transmissions have many closely-spaced ratios, so except at very low speeds (at the bottom of 1st gear), an engine may be kept close to its power peak for as long as desired. That means that a well-designed car that is driven well may produce a force F∼Ppeak/v. This depends only on the peak power (and velocity), and explains why the power-to-weight ratio is such a good predictor of acceleration performance.

Having said that, the torque peak is not completely irrelevant. Its position relative to the power peak is usually a good indicator of the size of the car's "powerband." Essentially, how high do you have to rev it in a given gear before the engine really gets going? Having a wide powerband is extremely important in everyday (or moderately aggressive) driving where you're not going to redline in every gear. It makes the car feel much more powerful even if the maximum performance is the same. Of course, a wide powerband is also useful if your have a poor transmission or don't want to shift as much.

Russ, differences in drivetrain inertia between reasonable designs are not usually not a huge effect. They're certainly significant, but I don't think I'd include them given the approximations already inherent in this sort of discussion.