Exhaust Configuration
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Discussion

steve singh

Original Poster:

3,995 posts

202 months

Friday 17th June 2011
quotequote all
Not sure I really want to ask the question on here - some of you guys can be quite harsh and some I suspect extract pleasure from doing that...but I'll give it a go.

Now go easy on me as I'm not that mechanically minded.

As I understand it on a 997 you have two exhaust boxes and they've split the usage of that between the pistons. As such if you see a more sooty tip on the passenger side of the car you're potentially in for a big bill (engine replacement / rebuild time due to pending piston 6 failure).

On a MK5 GTI I know there is one exhaust box (or whatever it's called) but two tips (this is where I will come across as stupid)...is the exhaust box constructed such to equally distribute the fumes down either tip and building on this does one set of pistons output to one tip vs. the other (as opposed to the fumes just finding path of least resistance)?

I'm sure it's a stupid question and you're going to give me hell for asking it...but last couple of weeks I've noticed the passenger side tip on my other half MK5 GTI is FAR MORE sooty than the other tip and Porsche paranoia has kicked in and made me think I might have an issue with the car.

I'm planning on moving the GTI on (see previous threads) and I absolutely don't and won't sell it to someone if there is an issue - so thought I'd best ask.

Thanks in advance and remember go easy on us novices...

V88Dicky

7,368 posts

212 months

Friday 17th June 2011
quotequote all
Are both tips in use? Some modern cars have 'fake' exhaust tips.

However, as all the exhaust gasses from your 4 pot go down the same pipe, I wouldn't worry about it anyway. What comes out of the exhaust tip(s) is what's leaving the cylinders.

ThomDean

56 posts

183 months

Friday 17th June 2011
quotequote all
As far as I know, the VW has a single downpipe, which leads through the Cat and into a single rear silencer, which then splits into two tailpipes. This e-bay advert shows the system reasonably well..

http://cgi.ebay.co.uk/VW-Golf-MK5-2-0-GTI-Exhaust-...

So I'd guess that the reason that one tailpipe is sootier than the other is nothing sinister. It might be that that's the path of least resistance, like you say.

No doubt somebody who knows a bit more will be along shortly with a better answer!

e635815

379 posts

217 months

Friday 17th June 2011
quotequote all
On some cars, even 4 pots, one of the two pipe is blocked by a flap at low revs. This ensure complience with noise regulation. The second pipe opens above a certain rev to achieve minimum restriction and better engine breathing.
If you mostly drive at low revs, one of the pipe will certainly be soothier than the other.
But the above statement has to be verified for your car.

Mr Whippy

32,453 posts

270 months

Friday 17th June 2011
quotequote all
On twin tips at opposing sides, the flow through one side vs the other will be different, unless they have balanced them across the rev range... not sure they will have done.

Apparently the E46 M3 flows 80% down one exhaust pair, and the other 20% out the other.

On the E9x M3, Dinan found that having dual twins (quads), actually cost efficiency due to the routing, so their solution is to have just the single pair at one side 'live' and the others are now inert!


You really need to know the exhaust config to get a good idea of what any signs on them might be telling you!




Mk5 GTi will have only one turbo, of that I am sure, so ALL exhaust gasses are mixed by the turbo no matter where they came from (cylinder 1 to 4).
Any soot discrepancy then is purely down to the flow at the back box. Possibly an active flappy exhaust as someone earlier said, or just that the 2nd pipe gets very little flow!? (kinda redundant but there for show ala M3 ones above)

Dave

Edited by Mr Whippy on Friday 17th June 10:44

steve singh

Original Poster:

3,995 posts

202 months

Friday 17th June 2011
quotequote all
Thanks guys - appreciate the responses.

The car does quite a few local journeys during the week (always brought up to operating temp) and receives a good run on the weekend (think upper rev range)!

I'll keep an eye on it and see how it pans out - probably always been this way but only caught my eye now and I'm getting paranoid !

RobCrezz

7,892 posts

237 months

Friday 17th June 2011
quotequote all
My old MR2 turbo (also a 4 pot turbo) did the same out of the 2 tail pipes. Pretty common apparently, the exhaust takes the simplest path and often one side is a slightly better route.

steve singh

Original Poster:

3,995 posts

202 months

Monday 20th June 2011
quotequote all
ThomDean said:
As far as I know, the VW has a single downpipe, which leads through the Cat and into a single rear silencer, which then splits into two tailpipes. This e-bay advert shows the system reasonably well..

http://cgi.ebay.co.uk/VW-Golf-MK5-2-0-GTI-Exhaust-...

So I'd guess that the reason that one tailpipe is sootier than the other is nothing sinister. It might be that that's the path of least resistance, like you say.

No doubt somebody who knows a bit more will be along shortly with a better answer!
That link was very useful and has helped reduce my fear! Thank you.