allroad V6 TDI slow build

[Foxpuppet]

http://www.fourtitude.com/artman2/up...ed_600_005.jpg

Funny I was only reading the write up on that guys car a few hours before you posted the pic. That's such a tidy looking ride. Like his wheels in particular!


Sent by courier pigeon

[gldgti]

Got a new drinking device

[gldgti]

So yesterday I spent 10.5 hours doing what felt like physical and mental endurance training.... otherwise called building a twin exhaust system from scratch. Basically it involved a lot of getting up off the ground and back down again, welding in awkward positions and fretting over symmetry, all the while hoping that when I finally bolted it all together, it would fit so I could just drive home.

Fortunately, it did all fit together. Actually it fits very nicely. Win!

But how about the sound you ask... well, yesterday I threw all i thought i knew about diesel exhaust out the window. Essentially, if you want a diesel to sound deep, throaty and rediculous, you have to get a v6 tdi. By the same token, if you wnat to completely ruin the peaceful hiway serenity that an a6 gives you, do what I have done.

After the drive home last night, I was pretty much disheartened and depressed, having cut up my old exhaust, spent all day fitting a new one only to have it so loud and droney that I literally felt like I didnt want to drive the car to work this morning. So not a great result there. The only plus seeming to be that indeed performance has been massively improved, particularly at low revs where turbo spool is much faster.

I did a bit of web trauling at lunch time and discovered that you can buy these cheap, crappy little exhaust tip baffles for (mostly it seems) subaru's with fart can exhaust, which purport to make long distance driving a pleasure.

Figuring I had nothing to lose, this evening I made 2 of them up. They basically slide neatly into the 4" tip of the muffler, and have a couple of transistion disks so its steps down from 4" to 2.5", then to 2". Gets retained in the tip with a little 5mm high tensile bolt.

I just went for a little drive and I reckon its shaved about 7-10dB off the noise right across the board, which is amazing IMO. I will wait until I do the commute tomorrow to pass final judgement, as I didnt really get to load it up like a freeway hill does. Even so, theres still some easy things like that I can do if its still not quiet enough.

Video is uploading now...
here it is: Allroad V6 TDI exhaust - YouTube

unfortunately the audio went crap. better to come this weekend hopefully.

[Greg Roles]

I've seen some trick weld in venturi's on a Audi TT site, drops the diameter briefly and supposed to be the go for droney cat backs....can't recall the site, will hunt.

Found it: 2 Venturi [VEN 200] - $15.00 : Techtonics Tuning, VW and Audi Performance Tuning and Repair Parts

[anthony--t]

Was going to flick you a text today and ask if you ended up doing it this weekend! - really sorry I couldn't come help

Awesome to hear about the power gains! Hopefully with a little fiddling you'll get the volume to your liking and everything will be golden, keen to hear it one day.

[gldgti]

thanks Anthony, no worries about it at all man you would have had much more fun in canberra

I am about 80% happy with the volume level now after coming to work this morning, a little more fiddling and it should be right. Thanks for that link greg, it has given me an idea and the final solution I think will have the baffle and an integrated venturi pics to follow...

[Ryeman]

I had an idea, some time ago, that it should be possible, theoretically, to place a 'bug' at/near the exhaust tip and tune in on your ICE.
I cant believe it not on go-fast shelves already.

[gldgti]

Do you mean play you exhaust sound on your stereo? Not sure I would want that. Perhaps noise cancelling though, that might be better.

[gldgti]

here are my quick and dirty baffle/venturi plates:

[anthony--t]

I'm not sure I understand. Do you put them in at the exhaust tip and they're held in with a small bolt each? And I'm assuming it's just quieter due to the inner diameter being so small?

[gldgti]

Well, exaclty how it works in this case is probably not possible to understand without some kind of flow analysis, but it seems to work pretty well. The internal pipe through my mufflers is 2.5" (63mm). The venturi pipe in my baffle plate thingy has a min ID of about 47mm, so its a bit of a decrease in size there but not heaps. I think the biggest thing is that the muffler transitions smoothly from the straight through perforated 2.5" pipe tothe 4" tip, which seems to let a helluva lot of sound out - nothing is reflected off the back wall of the muffler, its just funnelled out and almost amplified i reckon. The glass packing just takes the harsh raspiness out of the sound.

by adding the baffle plate, I think i'm helping to contain some of the sound pressure waves within the muffler to be dissipated by the glass pack. Its all theory at this level but it makes sense to me.

I just drew this up - its basically to scale

[Mysticality]

Video is uploading now...
here it is: Allroad V6 TDI exhaust - YouTube

unfortunately the audio went crap. better to come this weekend hopefully.

Oh good god that sounds amazing.

[gldgti]

I made one more little modification to the baffle plate on Saturday and now I'm pretty happy with the sound. Its still got a resonance between 2200-2800 but its much more bearable than without the baffle plate. I cant tell any performance difference between having the baffle in or out - which is no surprise given that the size of the exhaust is way bigger than necessary. I think the main reason I've seen the performance gain is because I have got rid of 2 cats and 4 mufflers and replaced them with 2 mufflers (much larger) and 2 baffles (same min ID as stock pipes).

I still have the cat in the downpipe to keep it legal and help reduce the NOx.

[Ryeman]

To me, it sounded like a tractor within that closed environment.
Do you have a drive-by highway recording for a better appreciation of the mod?

[gldgti]

not yet mate, still havent managed to get one will try this weekend though