S4 Exhaust Help

[nemo2182]

Evening all,
Looking to replace my B5 unit,and wanted some advice....

Now I had my eye on the dual 2.5" Milltek, but now im wondering after I spend nearly 2 grand, am I getting the best for the following criteria.....

Sound - Dont want to sound like a "v8" 1.2 corsa, but would like a nice burble on idle and throaty tone under hard throttle

Performance - Was told by MRC with pre-cats out and sports cats I could see 340bhp after fitting + 2nd remap, its currently 320bhp with standard unit. Im also one for bottom end power, so I like the gain in torque as well as BHP. Could I do any better with something else??

Price - Like I say, with sport cats its £1800 b4 fitting. Is there anything that is as good for less??

As always, any help would be appreciated.

Nathan

 

[aragorn]

TBH, thats a complete rip off.

I'd find a decent local exhaust fabricator, and get them to build a twin 2.5" system with a 3.5" X pipe.

Get yourself a pair of those ebay bargain downpipes (or you could always gut your existing units and fit sport cats to those) and you'll pick up a pair of decent sport cats for 2-300quid. The system itself shouldnt cost any more than 400 fitted.

 

[nemo2182]

Are these any good????

http://cgi.ebay.co.uk/AUDI-S4-B5-2-...arts_Vehicles_CarParts_SM?hash=item43999f3a82

 

[hardhitter]

The Milltek Dual 2.25" is the best off the shelf exhaust for the B5 S4 IMO. They are very quiet with the standard cats in the downpipes. You either take the pre-cats out of your standard S4 downpipes, or fit RS4 downpipes with the pre-cats removed (which is popular and will gain more). RS4 downpipes are fairly cheap s/hand and work well. The only thing is the RS4 downpipes connect up to the system differently (slightly diff length on one I think). it's no big problem for an exhaust place or somewhere like MRC to do.

As I said the dual Milltek is very quiet on idle, full chat and all round with std downpipes. when you remove the pre-cats or do the RS4 downpipes they will start to make a bit more noise but it won't be loud by any means.

aragorn- an x-pipe would probably do more harm than good as you are trying to keep each turbo seperate and reduce back pressure. I think most exhaust fabricators would recommend a single system as it's easier to make for them. If you can't get them to make a full dual system and that's what you wan't I'd stay away. Some of the better exhaust fabricators would do it, don't know how much cheaper than milltek though.

I wouldn't like to comment on the quality of the ebay systems and downpipes. What i know is the S4 / RS4 downpipes are a pain to fit and they need to be absolutly spot on, any downpipes that haven't been jigged correct would be apparent when fitting. Similar story with the system, but not as critical as there isn't much room for error when fitting a dual system. great if they do fit though !

 

[aragorn]

They seem to get a decent write up. Quality can be a bit hit and miss, sometimes needs a bit of fettling to fit, but if your getting someone to weld in the sport cats anyway the exhaust place can tweak it to fit.

 

[aragorn]

A Mate of mine had a 530i V8 BMW. The stock exhaust rotted out and BMW wanted about 1200quid for a new system.

He had a dual 2.5" system made up by a local place for £350 in stainless.

£1800 for the milltek is just rediculous, and personally, 2.25" is a bit too small.

 

[AndyC]

there is no definative exhaust tests out there it seems

twin is "supposed" TO BE better...... but is it really.

 

[AndyC]

there is no definative exhaust tests out there it seems

twin is "supposed" TO BE better...... but is it really.

 

[mwarrey]

A few years ago I was considering a milltek and was at the AMD stand at Audi Inters. There was someone there from Milltek and I asked what the difference between the dual (rs4 type) and single system. His reply was that the main reason they produced a dual system was to satisfy their market in America and that their single system was better.

I still however have the standard system on my S4!

 

[S4 IRL]

I have just removed my milltek dual, And have ordered a jetex cat back, will have it monday 16/05, Not bad money for it either. Taking a chance on it as i dont think many use them on the s4 and i cant find any reviews either, but it was recommended to me by pw motorsport, I have RS4 down pipes with gutted precats, will be fitting it monday night, Let you know how it goes.

 

[dest]

Ive got XS Power downpipes and full system (2.5" dual) with no cats or precats, its running 480bhp no problem and sounds awesome!

 

[Foxmeister]

As Dest says, most folk have went for XS system lately, and all are happy with sound etc, sometimes fit isnt perfect but any exhaust place will cure this, cant complain for the prices, very competitive. Personal choice at end of day thou.

 

[dest]

My downpipes were modded to add in flexi's, which any decent exhaust place should be able to do.

Two totally crap videos of the sound:

 

[AndyC]

I am hazy on twin turbo exhaust theory.

2.25" ID gives 15.89 x sectional (if my maths is right)
3" ID gives 28.27

giving just under the x sectional going from twin into single 3"

 

[aragorn]

a twin 2.5" exhaust has an area of: (3.14*31.7*31.7)*2 = 6330mm^2

a single 3" has (3.14 * 38.1 * 38.1) 4558mm^2

working back, you'd need a single 89mm exhaust pipe to match a dual 2.5 in terms of area... ie just over 3.5"

 

[AndyC]

thats pretty much what I worked out, as the 3" is about 2" less x sectional under the overall 2.25" x sectional.....

however I am not sure if its actually a problem, as if it goes too large the temps can drop and it will slow the gas down.....

I am not sure if anyone has done any testing on this

 

[aragorn]

"Too large" doesnt really matter on a turbo car. After a turbo you want the biggest pipe you can sensible fit. 4" drainpipe out the wing would be optimal.

Pulse tuning and exhaust gas energy etc only really matters pre-turbine. The turbine itself works on pressure differential, bigger exhaust means less pressure, which means the turbine works more effectively.

 

[AndyC]

I have always believed this to be the case, i have a funky design that the rally boys use.. (conical expansion chamber post turbo)

but its the difference for twin turbos is the difference I wasnt sure about