Originally posted by |Maku|
Cheers,
Steve
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Probably because a 3" pipe will not go over the coupe back axle. It is the major stumbling block to putting a large diameter exhaust on a coupe...
Cheers,
SteveThe Perfectionist
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Audi Class Concours winner Stoner Park 2014, ADI Concours D'Elegance Class Winner 2008, Runner up 2014. Winner, S2Forum Show'n'Shine Billing 2006 & 2008.
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i have 3" over rear drive shaft
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Friend of mine suggested:
1. 3" downpipe;
2. 3" pipe instead of cats;
3. 2,75" pipe before middle muffler;
4. 2,75" pipe between two mufflers;
5. 2 x 2,75" tips.
What do you think of this?
To "s2avant": when its warm, how does it sound at 50-60km/h with 3-4th gear and cruising at 110km/h with 6th gear?Comment
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I get a resonance at certain RPM around 50-50km/h in 4th and 5th. Cruising in 6th at 110km/h is more a background hum than a drone.
Benthe best intentions are fraught with disappointment - gil grissom
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1994 ABY Avant - it's getting thereComment
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Just read this through for the first time - my thoughts:
What exhaust does Angus have on his RS2? Goes like hell, and is really quiet.
Anyway. My Longlife is quite noisy - but the external wastegate doesn't help with that one
It's loud to start on a cold morning - once it's warmed up, on idle, it's got a raspy burble and sounds rather nice. It's boomy at 2-3K rpm, once above that there's no boom and sounds like a wild animal 
I only have the one box... I think it's a bit noisier than I expected, but I just remind myself that it gives better performace that way I've been in David's car with a 2-box Longlife I believe and I don't remember it sounding at all boomy in the cabin. ANyway, once you're over the about 3000rpm the external WG pipe drowns it out anyway. I'll report back once I get a 3" downpipe fitted! 
For any 3B car that is pre Aug '92 registered, I'd recommend getting it done DP-back in 3" S/S as a replacement for the de-catted twin-pipe section.
RossAUDI - saving Dad's from minivans since 1994
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The reason why I asked it is that right now my s2 avant has 60mm pipe "downpipe-back" to the end where is 300mm (lenght) muffler and thats it. Previous owner has made such a terrible exhaust that when I drove with the car for the first time I thought that there is no muffler at all!!! If the result with a 3" exhaust (two mufflers) is the same, then I dont want it.
I have S2 coupe as well and it has sport exhaust by SKN. 70mm downpipe, 2x64mm in the middle and again 70mm pipe with two mufflers. This is the best exhaust system I have ever had. Its not too loud but it gives a hunch that car has sport exhaust system.Originally posted by s2avantComment
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Exhaust Pipe Size.
- Bigger diameter bores are not always better.
Because of the big weights of big diameter exhausts and big diameter silencers, bore sizes should be kept as small as possible while still allowing maximum flow.
A good guide, based on the experience of tuners is as follows:
1300-1600cc – 2.25 to 2.5in
2000-2300cc – 2.75 to 3.0in
2500-3000cc – 3.5 or 2x2.5in
3500-4000cc – 4.0 or 2x2.75in
5000-5700cc – 2x3.0in
These figures are based on engines developing 120-150bhp per litre.
Rally engines developing 200-250bhp per liter need pipes that are 0.5 to 1.0in bigger.
The tailpipe can be reduced by 1/4in without suffering penalty.
But testing is the only way to go. On group A two litre turbo engines, a 3in pipe will give excellent power but a pipe 3.5in will cause a power drop and at 4in the power comes back. So testing is the only reliable method for choosing max power setups.
With turbos, the biggest flow restriction is at the turbine wheel and housing. The use of a bigger housing, without suffering further turbo lag will give better gains than exhaust change. Then next most restrictive area is at the manifold between the turbo and the head, so improvements here will also give good gains.
Tailpipe Design.
-Can use a tailpipe or use CATs, baffles and silencers.
After the header, we have to consider the rest of the exhaust system. On all out competition cars this can mean just a tail pipe. On road cars to usually means a cat and one or more silencers. Less tailpipe length will increase top end power and longer tail pipes will yield more low and mid range power.
This is why some engines will have a tailpipe not much longer than the collector. However, most tailpipes go right to the back of the car.
Tailpipe diameter is determined on the dyno and if a cat is used the diameter after the cat needs to be larger.
A guide to blown and nitrous engines is:
80 to 120bhp – 1.875in
110 to 140bhp – 2in
130 to 150bhp – 2.125in
140 to 185bhp – 2.25in
180 to 220bhp – 2.5in
210 to 265bhp – 2.75in
250 to 320bhp – 3.0in
280 to 360bhp – 3.5in
400 to 500bhp – 4.0in
480 to 630bhp – 4.5in
580 to 750bhp – 5in
As always the entire system must have a minimum of bending and adequate bore size. When ground clearance is a problem then oval exhaust bores can be used with no penalty in flow. You can reduce the diameter by ¼ in at the end (beyond the real wheels) without incurring any flow restrictions.
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Have anyone reduced tailpipe by 1/4??? It sounds logical that when exhaust gases aint so hot anymore,then they dont need so much cubic measure anymore. But have anyone tested it??Last edited by |Maku|; 15 March 2006, 12:42.Comment
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