ian8

I am weighing up the choice between the S8 and the A8 4.2TDi. Obviously the S8 is quicker at the limit, but if in spec as close as possible- how big will the real world difference be?
In gear acceleration at normal driving revs I have the impression there may not be much in it. The torque of the diesel vs normal driving revs could feel just as responsive. The longer range on a tank with the diesel certainly has an appeal, my current S8 seems to need to stop for a drink annoyingly often at times. Which would you choose? Why?

audiboi

4.2 TDI is hot too

Der Kimbo

It won't be as spriting a drive as the S8 in the handling department, but the perceived speed will probably be close to the same. The Diesel has tunability up to 400bhp+ and over 600lb/ft of torque.

TheBrit

The 4.2 TDI was my 2nd choice if the S8 had been overpriced (it's not cheap, but compared to the W12 it's a bargain!). The reason I went with the S8 is that having had an RS 6 and a W12, I felt that a slower A8 would feel like a downgrade. I think that coming straight from a D2 S8, the A8 feels like such an upgrade in dynamics, comfort, luxury and technology that the performance wouldn't matter, but the 4.2 TDI will probably feel as fast as your S8 anyway, so you win both ways.

An A8 with sport suspension and the 4.2 TDI engine makes a very good all-rounder, and is still faster than most cars on the road, despite having the thirst of an average family saloon when driven sensibly.

One last thing - try specifying a 4.2 TDI with all the things you get in the S8, you might be surprised. My S8 with the options I put in has a lower OTR list price than a 4.2 TDI with all the options to bring it to the same specification so that only the engine is different. You might get more discount on a TDI, which might tip the balance back.

ian8

No I am not North American, and I am selecting a car for driving in Australia.
I have had a loaner D3 A8 4.2 before and was very surprised. It definitely felt sluggish compared to the S8.
Even my wife, who normally would tend to prefer a more comfortable ride, noticed at about the first real corner when she was driving that it was a big step back in dynamics too. The sport suspension option may overcome this, and in gear I am hopeful that the TDi is a significant step forward over the petrol. I was disappointed by the petrol 4.2, as the power is not a big step back and there is an extra gear. There is a big weight difference though and higher gearing. I will have a drive for around 3or4 days in the 4.2TDi very soon. We have a golf 2.0TDi as a 'shopping trolley' and it is very impressive.
240kw may be a step back from the 265kw on my S8....but the 240kw is at 3400! This is not so far from typical driving revs and generally there is way more kw at the actual rpm is use when driving.
Now the new s8 has rpm the S8 has 330kw...a significant diffence (25% more power, 15% more weight) so it should be better again. Still that power is at 7000rpm, which only happens when I am driving very breifly and quite rarely. At typical RPM the power is going to be not as different from the TDi ...and the torque will be less.

As for price...you defintely have a point on that one! Here the S8 has the B&O std and ceramic brakes as an option. THe TDi doesnt have the ceramic brake option and the B&O costs a bomb!
There are several other things std on the S8 that are extra on the TDi too...

So there is almost nothing in it cost wise and having an S badge is just a little more special if nothing else.

The issue is just how much real world performance difference (I find extra torque is very pleasant) and that benefit of less having to stop for the maintenance of refilling the fuel.

Feedback appreciated!

ian8

I would delete the V10 badges if I do choose the S. I would probably delete the 4.2 indicator on the TDi too...nothing too overt.

Having an S certainly is an attraction

ian8

I wonder how much improved the suspension is on the S8 over the regular sport version? Some reports have also claimed the S to ride better as well....could this be lower unsprung weight of the ceramic brakes on the cars they tested??

I will have more of an idea after a few days in the TDi, but there could be a significant delay on getting the same opportunity in the S8

TheBrit

band means you don't use the engine's ability all the time, but it is very drivable on the bottom half of the rev range; still faster than most cars on the road!

The TDI will rev low even at cruising speeds, the gearing will be so tall compared to your S8 it will feel very relaxed at speed.

I always thought of the sport suspension in dynamic mode as having the handling of the D2 S8 with the flat cornering of the RS 6, but with the relative comfort of a regular D2 A8 suspension in comfort mode. The sport suspension on the S8 is better than the regular A8 sport suspension, at least in the UK; the ability to soak up shake from rough patches of tarmac and crashes from poor repairs or small potholes has been improved, but it's still flat round the corners.

I think that you'll find the S8 has much better inital acceleration from a standing start, mainly due to it's very low gearing and free-revving engine, but once rolling, the TDI will almost always accelerate as well as the S8 in any given gear because there's two metric tonnes of car to haul along, and the torque of the TDI helps a lot. The S8's talent is in dropping down a cog or two and holding on to the gears for longer because of it's higher rev limit.

Of course you need to try both if you can.

ian8

I have read that audi limited the torque of the TDi as 650nm was all the gearbox could handle. I dont know how they do that but the strange rating of peak torque being available all the way from 1600 through 3500rpm without ever actually exceeding 650nm.
On this basis it would seem very easy to 'chip' the engine to raise maximum torque, but wouldnt it also be very unwise??

TheBrit

If I remember rightly, the RS 6 gearbox was listed by ZF as having less than the 560 Nm peak that was going through it.

Now if Audi could make the 6 HP 32A gearbox fit, that rates 770 Nm, so in theory could possibly take a higher peak?