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OK so now I've had both cat-back systems on my car and have used them for a good few weeks, heres a bit of feedback.

DUAL:
This is a superb system. Truly free flow. Really allows the engine to rev freely and the power is delivered smoothly with no hesitancy or flat spots.
Tailpipes are big and meaty. Since the system uses twin piping however, the system sits quite low and you can easily scrape it on the odd speed bump if going too quick. This is even with normal ride height.
Also, the noise. Its got a nice deep throaty sound at idle and a clean and crisp whail when blipping the throttle. Although addictive at first, when the exhaust warms up, there is a boom at around 1500-2500rpm. This is fine for motorways as you tend to sit at higher revs than that and the exhaust tone is virtially stock, with a nice deep burble when accelerating. However this rev range gets used a lot in town so the drone can get to your head. I suppose this is the only downside to the system. You may like to know that although the RS4 Milltek uses a dual pipe design as well, it is more baffled and uses a different design of boxes and pipe entry/exit, making it quieter than the S4 variant.

Single:
I think this is a pointless system. After having the dual, the change in exhaust note is virtually not too different to stock. OK so its a bit deeper that stock on idle, but throughout the rest of the rev range, you can hardly hear it.
It also doesnt seem to flow as freely as the dual. I immediately noticed that the hesitancy in the power returned again after having the dual and now had a flatspot again at low revs before the car lurched forward at around 3500rpm. The tailpipes look a bit tame and very much stock too as compared to the clean and crisp cut pipes of the dual.

Personally I would go Dual, if you can bear a bit of drone at low revs in town. And for all those that said a cat-back makes no difference, it does. It may not make a siginificant difference in power or torque on the rollers, but you certainly feel it on the road as the engine revs quicker and provides cleaner power delivery.

Hope this helps for those thinking of buying a system

Thanks.

thanks for the feedback, very helpful. What is the diameter of the pipes in dual system?

Anyone else have any feedback on other systems eg the awe

Cheers
Tony

Milltek Dual has two 2.25 inch pipe runs.
The Milltek Single has one 3 inch run.

so i assume that the single 3 inch would have greater clearance problems than the dual pipes.
Are the factory pipes that much smaller so as to not scrape over speed bumps etc?

My Miltek single knocks on the body work. Been to three different places to get it sorted, all say it's fine but it still knocks. Seems to only happen after period of sustained right foot usage...

Not heard the twin but very pleased with the sound of the exhaust. I also have APR downpipes so perhaps helps it breath and sound better.

My Milltek also hits the underneath of the car and is very annoying. I would disagree regarding noise of the single set-up, I find that it is loudest inside the cabin at idle-2K which isn't very pleasent due to the booming. Once your up the rev range it's a little more 'fruity' than stock but not a hugh amount.

The fit of the Milltek seems very bad for the cost of the exhaust. I also have had AmD try to correct the problem on a number of occasions without long term success.

That's interesting. My new S3 has a Miltek exhaust, and that too knocks badly.

If you could supply me some pictures I can try to help if you like.

john@thorneymotorsport.co.uk

Nice review. I am that cynic with respect to CAT back systems.

What amazes me is that I've never seen a proper rolling road test done with any of the so called performance exhausts. on any of the A4/S4/RS4 forums.

I think the only thing that comes close is a in car dyno test done by Don Parlik or something like that on Audi world.

I've never heard of this knocking problem before -not good when you've shelled out £450!!

Currently have a an apr chipped car with stock exhaust.
Would i have to get the car remapped again after fitting the milltek?

Steve

No for a CAT back only. You would/should if you go for sport CATS.

Thanks Golich.

I have an APR cat-back and I am impressed with both the fit of the system (never had a knock / scrape yet on RS4 suspension), and the sound of the exhaust (slightly louder than std on tickover, much throatier past 4k outside of the car, whilst remaining pretty civilised inside. As for power increases, don't expect miracles, but they should make the engine rev more freely and give a few bhp - I think the deciding point for some people is a lifetime warrantly on stainless exhausts (and that they probably cost less less than the OEM Audi price if your exhaust needs replacing.

I have a single pipe system and can't say that it knocks on the body. It does scrape a bit over 'some' speed-bumps, but then my car is lowered. When first fitted it was loud and then got quieter when (I presume) it sooted up. It then when louder again (when the Miltek cats were fitted).