This is a great thread, which I would like to see more on. I myself am struggling to find real performance upgrades for my 4.2. There is all sorts of stuff for the 2.7T however I have yet to find much for the 4.2. I did find a chip that costs $595 which claims 12-15 awhp gains.... which seems 'dern unreasonable for something you likely will not notice. I can't even find exhaust mods.

I would like to know more on this topic as well!!

Welcome to Audi's 2.8 and 4.2 world (no one cares about non-turbo's).

remember, theres about 20% loss with quattro so that 12-15 hp that seems very little, is probably more like 20 hp. that is not too bad imo for a na engine chip. There are plenty of exhaust options. Cargraphic has a NICE system for the 4.2 and I think LLtek has one as well. Then theres always magnaflow mufflers, they sound great. Remus may have one for the v8 as well.

Well it is hard to say on that chip. The chip I am referring to is the GIAC chip. One vendor promised 40 hp, another promised 20, and another, 12-15. I would be inclined to go with the 12-15 as I personally have seen similar results with other cars- The Audi world is just new to me. Anyhow, I'd rather not spend $595 on that one yet. The transmission chip sound worth it, just to save me the frustation of the laziest shifts I have ever experienced in a car. I love this 4.2 but the tiptronic is slightly frustrating for people who like to 'drive' their cars.

As for exhaust- I am looking for 100% performance... not sound. I want to keep it quiet, but I noticed the actual lead pipes are TINY on my car. No mandrel bending, etc. Are there GOOD systems out there that aren't loud? I don't want this thing loud at all- Maybe a slight increase in low tones, but, I definintely don't want it loud. Any suggestions on that? I will Google those vendors you listed in the last post too....

Well, if you get a resonated system, it wont be too loud. The LLtek system advertises a nice deep tone thats not intrusive so that might be a good choice... however I have never heard it or heard anything about quallity so that may not be the the best. Remus is not much louder than stock but its only rear mufflers(axle back) so you would have to do something else if you wanted to change it up front. I will say that when I put my Remus mufflers on, I noticed a big difference in how the engine felt inn the mid range. If you are interested, I can send you some videos of my 2.8 with Remus.

I would definitely be interested in that. Thank you!

Yeah, if I got any 'added' sound out of the exhaust, it would be just that- Some deep v8 grumble. I was a little surprised at the lack of 'grunt' it had. I'm in a whole new ballpark now with refined german luxury, I know.... but I am used to American V8's. I recently got rid of my 1996 Trans Am which sounded like ear candy. We also had a 5.9 Limited Jeep which also sounded LOVELY... and now have a Denali XL with the 6.2L that sounds even better. So I was just put aside for a moment when I heard the Audi 4.2. It packed the punch I wanted, so I didn't care after driving it Plus, it IS a luxury car!

Anyhow, thanks for the tips.. I would like to see those links for sure. i will check out those systems you reccomended too.

beware, the 4.2 engine itself has changed drastically

I am sorry, beware of what? Are you referring to all of the differences between c5 & c6 4.2's and S6 & RS6, A6 etc? As far as trying to do the same thigns for performance upgrades? Is, is there something baout the older 4.2's we should be careful of?

Well, after 06 I think, it goes to FSI so it has 4 valves per cylinder instead of 5. Not sure about other changes, but Im sure there are some... after all, it IS Audi.

Thanks all for input so far but no one seems to recall or able to answer my fundamental question which I am now better able to articulate:

What is the difference between the 2003 A6 4.2L and the 2003 S6 4.2L which is an A6 with reportedly ~40 more HP. I have the repair manual which covers both engines and they have the same repair procedure for everything (just show the procedure applies to both engine codes). So basically I don't get the difference. If the S6 has 40 more HP in the same motor than there IS some mod out there waiting for me to find.

PS. I am waiting for RevoTechnik to prepare an ECU flash more my car (seems my ECU code was one they did not have a program off the shelf for) and the feedback from my local tuner is the ECU upgrade adds a little bit of noticeable power but most of the benefit is elimination of the hesitant tranny response.