daf999999

I have to believe this has been discussed at great length - my search skills must be bad today. So sorry if duplicative, but I'd like to hear impressions about the new V8 turbo vs old V8, particularly in a NWB and including mpg experiences in heavy city traffic. Thanks

DeerHunter

I'm not from the A8 camp myself, but I do have experience with variants of the 4.2 V8 (in my B6 S4 Cabrio) and the 4.0T (in my S6). In short, it's a huge step up. The turbo motor has waaaay more low-end torque and, with cylinder deactivation, mileage is better as well. You can have your cake and eat it too.

Dr.Aronis

There is no comparison. The turbo is better in every way possible. More power and better mpg.

derfA8L

I'll take an opposing view from the above opinions:

If given the choice, I'd take the 4.2 normally aspirated V8 due to no turbo lag. I believe the new V8 is much improved over prior turbocharged Audi engines in this respect, but turbo lag is still present to some degree. While others may enjoy it, I'm not a fan of the neck-snapping you get upon hard acceleration when the turbos kick in---much prefer the smoother more linear acceleration of the normally aspirated 4.2 engine. As for fuel economy between the two, the 4.2 V8 is comparable to the 4.0T...actually a trifle better than the 4.0T in LWB form:

From Audi USA (A8-Non "S" Variants):

4.2 V8- NWB/LWB: 17 City/27 Highway
4.0T V8-NWB: 17 City/28 Highway
4.0T V8-LWB: 16 City/26 Highway


However, at the end of the day it's all moot if you're looking at acquiring a new A8/A8L, since the only V8 is a turbo.

Dr.Aronis

I'm getting 25 mpg overall with led foot. My RS6 gets about 20.

Barmats

I had a 2012 A8 NWB with the 4.2 and it was just fine. Not immense power but a good amount when you pushed it. Then I drove a 2013 A8 4.0T LWB and ended up buying it. There is a considerable power difference in both hp and tq, but as was mentioned earlier it is not a linear power delivery with the turbos, which is quite all right with me. There were other reasons I traded up, but the engine was a big factor.

I am having some off-the-line lag issues which were not present on my 4.2, but I believe this is software-related and not turbo lag because it happens immediately off idle rpm when accelerating.

Interestingly, I had better fuel economy with the 4.2 and could get just over 33 mpg running at 65 mph on the highway with cruise on and a level grade. With the 4.0, the highest I've seen under the same driving conditions is about 26 mpg. While I know this is not representative of everyday driving, it is an interesting and significant difference between the two.