One more thing to point out us I think the s6 generally had 19x9 wheels although technically optional but everyone got them. The s8 is I believe 20x9, which may been optional only last few years of the s6? My real question is how much tire can you fit there without rubbing or rolling fenders, between the two cars?
Lots of good info CountVohn!
The S8 exhaust does look like it would flow better. Less kinks, smoother bends, and dual outlets from the mufflers.
vgvt, according to Tire Rack the S6 came with 265/35/19 tires and the S8 came with 265/35/20 tires. They are the same width but the S8 uses tires that are like an inch taller. With either car I would keep the same tire width as stock but go to 18 inch wheels with tires that have more sidewall percentage. 265 millimeters is wide enough to keep the spinning off the line to a minimum. But these big and heavy cars would really benefit from lighter wheels/tires just like lighter brake rotors.
Agreed! I went with 275/35/19 because that was the only comp size that would work on the wheel. It was actually only like .2-.3 wider than the 265 tho.
Looking back I wish I had gone light weight 19x9.5 with 275 all aroun. Perhaps 19x9 like you suggested would be ideal tho.
I’m not sure if we’re doing mechanical only, or if cosmetics and creature comfort are within the scope of this topic, but, this convo could be a Google result for “differences between the S8 and the S6”.
So how about room in the back seat for long legs and big feet? The A8/S8 is serious. That’s noticeable for us taller passengers.
Also, regarding cosmetics, and I can’t remember specifics, but I remember hearing somewhere that the VW/Audi interiors cascade down from debuting on the upper end Audis, and then appear a few years later in the lower end Audis, and then finally appear in the VW’s. Does the A8/S8 get the newest generation interior before the A6/S6?
Looked this up awhile ago, an you’ll be suprised it’s not extremely more spacious then the s6. Second row leg room is over 1.5 inches more, s6 has a touch more head room vs. S8. But the biggest thing that actually grinds my about the s8 is the trunk is smaller and not quite as wide. Could fit golf clubs much easier in s6.
No one has mentioned this but th steering setups look different servo in the s6 vs. Pwr rack and pinion in the s8. Not sure how accurate the rest of this link is though.
http://www.thecarconnection.com/car-compare-results/audi_s6_2007-vs-audi_s8_2007
Picking up where we left off.
http://audirevolution.net/addons/albums/images/619428370.jpg
There is a good reason why so many have seen a great big improvement going to a custom 3" exhaust for their V10 S6 or S8
The stock exhaust on the S6 and S8 are both the same size. The S8 has better bends and no crimp points, but both exhaust systems have the same small exhaust. They are not even 2.5" The 4.2 RS4 has a bigger exhaust than the 5.2 V10 S6 and S8.
The total size for the V10 exhaust is
http://audirevolution.net/addons/albums/images/852870710.jpg
Yes, that’s 2 3/8’ that’s is very small when you think about the total flow of the V10.
Still, we know the S6 and S8 exhaust are undersized but what are the other differences between the two exhaust systems?
Other than having much better smoother bends with no crimps the S8 has what looks to be an X pipe. We all have seen just how much power can be gained by placing a proper X pipe in an exhaust system.
http://audirevolution.net/addons/albums/images/140279339.jpg
The S6 has what looks to be an H pipe.
http://audirevolution.net/addons/albums/images/409900215.jpg
There are two very different parts to each exhaust. The real question is are any of these performance adding add-ons functional? Next week we will cut them open and see.
That’s interesting, why would Audi not put an x in the s6 vs s8
Its interesting they are both the same size. but that the S6 has all the smashed and mashed areas. Then the X Vs H section again is interesting to see. Im excited to see if any of those are functional.
I really think the only difference is starting to look like just the exhaust the air box and the gear raito.
Last we left off, we were waiting to see if the OEM Audi exhaust systems on the S6 and the S8 used the X or H pipe flow technology that we see on so many performance exhaust systems.
http://audirevolution.net/addons/albums/images/579069160.jpg
First up let’s look at the S6. What are the real differences between the S6 and S8? We can see the exhaust systems are different but is it enough to make the S8 have the extra hp?
The S6 looked like it has an H pipe. We know the added power gains of adding flow technology like an X section crossover or even an H, but did the Audi S6 team use it.
http://audirevolution.net/addons/albums/images/409900215.jpg
When you look further, there is no cross over. The section is just there to support the structure. There is no H pipe.
http://audirevolution.net/addons/albums/images/291302678.jpg
So far, we have seen the S6 has a more restrictive exhaust with crimps sharper bends and now no crossover section.
Now it’s time to move on to the S8.
Here is what the possible crossover section looks like on the S8
http://audirevolution.net/addons/albums/images/140279339.jpg
With a section that looks like that and with so many welds in the area there has to be something in there.
Sure enough, there is.
http://audirevolution.net/addons/albums/images/867033232.jpg
Sure, this is way less than optimal when it comes to a well-made X section but it continues the trend, that the S8 exhaust has more of an actual performance approach to it than the S6.
The more and more I look, the more and more the S6 and the S8 are not very far apart and it seems like closing any possible gap between the S6 and S8 is as easy as an exhaust and maybe a better flowing air filter.
No surprises there. How can we measure whether the s8 heat soaks less if at all 
Nit that important but what do prod numbers look like between the two per year?
Wow that explains a lot and shows a good argument on why the S6 guys see such great results with exhaust work. Espically when they get a real exhaust with a X pipe
I wonder if I can get just a real x pipe on the 8 and see if it helps it even more.
Yes it does. Basically fab speed setup Google that and do something similar ish
Do you still have the stock exhaust. If your close to the detroit area I would just have countvohn make you an exhaust. They made both my headers and catback.
Also the X section needs to be placed in a different location depending on your over all set up
What a rip off. It looks like the same size as stock and its not even a true X pipe. Your spending too much money to remove the resonators. What a waste. Why would you put a part on that creates drone. the resonators are there to cut down on the one thing that nobody wants drone.
Fabspeed this is a big PASS what a joke.
Yeah I was thinking the same thing. $1500 for more noise that the wife will hate and not get me what I want.
http://m.summitracing.com/parts/sum-640700
Something like this can’t be too much to get installed.
And I’m in MN so Detroit isn’t close enough that I could have something made.
I didn’t say buy fab speed, but I used there principals but with 2.75 inch piping and it worked great! For about 600 
btw piping on favspeed is like 2.5ish so rs still improvement over factory wth better config just jot ideal but the design is decent actually. Not as good as custom but usually isn’t
That would be a good thing to just swap out the current X you have and put that right in its place