Skinny downpipes and Cats begone with you!

[S4TAN]

Hello all,

Will attempt to answer your Q's!

If a Miltek cat back mates to a stock cat, then these new miltek down pipes and cat bypass pipes must end with the same interface as a stock cat with which to fit the Miltek catback. My logic says these would fit a stcok exhaust, but either way it's a question I'd like an answer to.

Can the link pipes be swapped out with cats at MOT time or is a complete downpipe change required?

Have you an increase in max maf reading Julian?

Is taht £200+vat per downpipe or for the pair?

You may be right about the pipe size Graham - but i'm not sure: the 3" came with reducing link pipes to fit to the stock d/p's - these had to come off to mate with the link pipes that came with the new Milltek d/p's - so there may be a size difference ... Doug will know for sure.

The link pipes wouldn't come off for the MOT - the whole d/p's would have to come off ... but there may be a way round this come MOT time ...

My MAF is already maxed out on vag-com (i'm informed that vag-com only reads the S4 MAF upto 335g/s - apparently the actual MAF sensor itself measures higher, but vag-com can't see it (I could be wrong here - someone else can confirm this maybe) - so I saw no difference in MAF reading with the new d/p's as i was already getting 335g/s with the stock (pre-cat gutted) d/p's ...

£200 +VAT for each d/p - so £470 all in.

Do you find that your turbo's spool up a tad quicker also and you have like 10% to 15% extra kick low down when you put your foot down?

hahaha - Saf; my arse-dyno isn't accurate enough to measure at such resolution as 10-15%, but yes - they do seem to spool a smidge quicker - but it's definitely the power difference above 4.5K that you really feel!

Did they come with flexis?

Yes - they sure do! They're very nicely made - a bargain for the money IMHO! If you consider that a Milltek 3" cat-back costs £460, and these d/p's cost £470 for the pair, then for less than a grand you can get a full Milltek exhaust system (albeit without cats) ... not bad.

How would you describe the percentage increase in the deepening of the exhaust note?

I would say it's deepened by at least 12.754962% But that's only a guess! Nah - only kidding - it's just deeper...

looking forward to hearing it Julian-is it as loud as mine??!!

No Adam - not as loud as yours mate; i think the 3" keeps the noise down nicely enough to not attract too much attention ...

Nice one Julian bet your motor sounds really mean now – ‘mmmm suit you sir’

Cheers Paul! It does sound good - DavidT heard it yesterday at Dougs and they both said it sounds really nice ... sounds good in the car too; not obtrusive ... but there's a nice deep bass hum that lets you know it's there ...

[tdiquattro]

Sounds superb

I have a related question which has been at the back of my mind for a while now...

- Stock pipes for every car come with what? - 300 cell cats of a certain internal surface area/volume?.
- Forgetting the pre-cats which we all get rid of anyway, the S4 has 300 cell rectangular section mains? and the RS4 200 cell round cross section mains? - correct me if i am wrong. The pipework is almost identical either side of them, maybe a restriction near the flexi section on an S4 but that's about it.

Ok the question - are 100 cell mains going to give you a pass at emissions check time?????
if so why dont the manufacturers fit them?
if not why bother with them / why does anyone manufacture them / why not just fit straight through pipes?

Am I missing something?

Nigel.

[S4TAN]

I think stock S4 main cats are 400 cell, and i think you're right about the stock RS4 cats being 200 cell.

Not sure about the 100 cell cats - but i guess they should pass, but maybe only just ... maybe lower cell-count cats are more expensive to manufacture(?) I don't know but there must be some reason ...

[GrahamS4]

Higher emissions standards in other countries most likely the reason.

[saf]

Cheers mate.

Im in the process of building a custom system for mine. Will be 3 inch downpipes and dual 2.75 pipes, with 2/75 tips (if they will fit) I think 2 boxes to keep the noise down, but tweaked to allow as much flow as possible. They will also look like theyhave cats althought they dont. The downpipes will be custom made but off the shelf from a reputable American company and the other half will be fabricated to my specification.

Im hoping that it will sound tame, but once you put your foot down, the exhaust starts to wake up and scream.

The main S4 cats are 400 cell for definite. They do pass with 100 cell cats, only just as youve said Julian. Most of the time they are fine.

Julian, when you get a chance please put some pics.

I didnt think that Miltek were doing 2.75 downpipe sizes. I know their original downpipe size is 2.37 inches each. So 2.75 is a massive gain. In fact they flow around 25% more. And the price is a third of what they normally charge for downpipes with cats. So a bargain!!!!!!

[S4TAN]

when you get a chance please put some pics.

yeah - I should've done this yesterday when they were being fitted - but forgot the camera ... not sure when my car will be up on the ramps again to take a snap ... it may be best if Doug takes a snap of the other set he's got there at the moment - probably easier to see properly what they're like just layed out on the floor before they get fitted to a car ...

They're definitely 2.75" (we measured them before fitting) - i think the history behind these new d/p's is that Doug asked Milltek to make some totally de-catted sets up last year ... and they've finally got round to delivering the first batch (or something like that)

[DavidT]

Nice one Julian bet your motor sounds really mean now – ‘mmmm suit you sir’

Cheers Paul! It does sound good - DavidT heard it yesterday at Dougs and they both said it sounds really nice ... sounds good in the car too; not obtrusive ... but there's a nice deep bass hum that lets you know it's there ...

It does sound nice, deep rumble but reasonably quiet. My dual with these downpipes & 100cel cats is much louder.

The single is a very good exhaust. I know this, as I had one before my dual

[DavidT]

Ok the question - are 100 cell mains going to give you a pass at emissions check time?????
if so why dont the manufacturers fit them?
if not why bother with them / why does anyone manufacture them / why not just fit straight through pipes?

Am I missing something?

Nigel.

As others have said: S4 has 400 cell main cats, RS4 has 200 cell mains. Both have pre-cats.

Cars pass the MOT fine with 100 cell cats, not a close run thing from what i've seen. Some even pass with no cats

New cars have to pass strict emmissions tests, EURO 4 in Europe, other legislation applies around the world. This is very strict with tests on startup and all other types of use. The MOT is a very basic and easy test to pass.

[saf]

Yes I agree with that David as mine passed without cats. Just passed that it. With 100 cell cats they pass fine as long everything else is in order.

I just bought a set of ASP downpipes. Those are the ones I mentioned earlier. Monday I will try and and find out for sure what im going to do. So far Ive cadded out a nicely set of flowed 2 x 2.75 inch pipes, with two boxes as I dont want it too loud.

I just picked up the downpipes now, so I need to get the car on the ramp at my friends exhaust shop, then see if what ive designed will fit okay or not. Ive tried keeping it as close to the Milltek design as possible, trying to make it flow a little better at the bends. Im possibly thinking of putting a single resonator on each pipe then a back box towards the end with dual 2.75 pipes. It all depends what will fit, as I want a knock free exhaust.

Ill be using the V band couplings all the way down the exhaust as well.

Sorry to Hijak your thred Julian. Tell me what you think. It cant beat yours for value though. £47o is an absolutely bargain mate. I might even check with Milltek to see if they can do me a dual box with 2 x 2.75 pipes instead of the usual RS4 2.5's or the S4's 2.25 pipes.

Heres two pics compared to stock.

Mine are the generation 2 version, with the v band coupling flanges and the round style sport cats. So slightly different.

[S4TAN]

Sorry to Hijak your thred Julian. Tell me what you think. It cant beat yours for value though. £47o is an absolutely bargain mate

No worries saf - i only started this thread for general info to other members. Those ASP pipes look very nice mate.

[saf]

I just hope it will sound as I hope they will.

Time will tell.

[nickb834]

How is it that I find myself mildly aroused by some steel tubes.............?

Oh dear

[saf]

How is it that I find myself mildly aroused by some steel tubes.............?

Oh dear

only mildly?

I got them yesterday, and spent a good few hours playing with my tubes!!!

[tdiquattro]

Thanks very much chaps, that clears up my question, I will have another look at my downpipes and see what to try, great info as usual thanks again

[lemond]

Not the old 'dog' (woof woof) trick for MOT time then is it!....