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Discussion Starter #1
Can someone tell me what part of the exhaust does the X-pipe replace?
Are there any disadvantages to fitting one?
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
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Not the expert
you can see my thread that has pics of the underside of my car.

http://www.slkworld.com/slk-r171-general-discussion/174881-my-baby-had-operation-kleemann-ecu-tune-headers-downpipes-vids.html

I do not have x pipes but xpipes connect from the 1st set of cats usually to the 2nd set of cats or resonator before the muffler provided any of those have not been removed for better sound.
the x and y pipes like straight pipes allow the 'gases' to get out faster as there is less angular directions to travel.

Our experts will jump in and or correct me!

my new straight pipes and old oem pipes
 

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Discussion Starter #3
Hi Jeff,so the x pipe does not replace anything?
 

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Premium Member 2005 SLK55 AMG
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The x-pipe usually replaces the centre resonator, which is between the primary and secondary cats. The reason I did it was so that I could hear more 'growl' from my V8, so I also had the secondary cats removed at the same time too (and it definitely gave me more 'growl')! >:D

As well as increasing the sound, the x-pipe allows exhaust scavenging, which I've seen reported as potentially increasing power output (but only very slightly).

Click the x-pipe links in my signature for a thread showing before and after pics of mine, as well as a link to a YouTube video too. :grin:
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
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it replaces the original piping between the engine and the tailpipe as explained by my friends above.

an example:

 

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Discussion Starter #7
The x-pipe usually replaces the centre resonator, which is between the primary and secondary cats. The reason I did it was so that I could hear more 'growl' from my V8, so I also had the secondary cats removed at the same time too (and it definitely gave me more 'growl')! >:D

As well as increasing the sound, the x-pipe allows exhaust scavenging, which I've seen reported as potentially increasing power output (but only very slightly).

Click the x-pipe links in my signature for a thread showing before and after pics of mine, as well as a link to a YouTube video too. :grin:
Thats great info.
The before and after pics are interesting.
It sounds so good.
 

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Discussion Starter #8
Now I see the attraction of the x-pipe:wink:
 

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Discussion Starter #9
When the secondary cats are deleted do you get any warning lights that need to be coded out?
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
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O2 sensors are usually in the 1st set or primary cats, nothing in the 2nd cats.
 

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Premium Member 2005 SLK55 AMG
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When the secondary cats are deleted do you get any warning lights that need to be coded out?
As Jeff says, the sensors are on the primary cats. I no longer have secondary cats, and I get no warning lights! :grin:

My car hasn't been through an MOT yet, but I've read about others that have, with no issues (as long as you keep the primary cats, which I have). :smile:
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
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one of my pics show where the o2 sensors are plugged in but my ecu tune has taken care of any 'errors' since i no longer have primary cats.

 

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one of my pics show where the o2 sensors are plugged in but my ecu tune has taken care of any 'errors' since i no longer have primary cats.

Interesting to see that you didn't opt for the cross over pipe in the middle and just went for straight pipes ... any reason for this?
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
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No real reason. straight gets the 'bad gases' out faster. X makes a little wiggle!
And the fastest distance between 2 points is....... a straight line! :D
 

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Premium Member 2005 SLK55 AMG
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Hi All
@ Hugy take a look at the following youtube clip http://youtu.be/Y0Va3sDhqwI . As some have posted above the Xpipe only replaces the centre resonator ,You can keep all four CATS ( as I have) this will increase the sound coming out the back . Afew here have taken the option to have the rear two CATS removed to give more sound . Its up to you which way you go . But I will say try to hear in the flesh the two versions before you go the head .


Cheers


Andy
 

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Premium Member 2005 SLK55 AMG
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@hugy, Andy ( @ZeroZero ) makes an excellent point... taking the secondary cats out definitely makes quite a bit more noise... this is particularly noticeable at cold startup (I guess it might upset the neighbours if you do this often and too early in the morning), and whenever you give it some beans (it's impossible to overtake without being loud)!

Although I posted a video of mine, it sounds even louder in real life (the video just doesn't do it justice)!
 

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Premium Member 2012 SLK55 AMG
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Looks like you've pretty much covered everything here already guys and I would agree that technically the X-pipe replaces the resonator and effectively does the same job, balancing the gases and improving performance slightly with better scavenging less restrictive flow etc.

I deliberated long and hard about going with a straight through exhaust mod but everything I read suggested that V8 engines like to be balanced and preferably as close to the front as possible.

Losing the secondary cats allows you to put the x-pipe closer to the front than where the resonator sits and removes another restriction, so I went for that. I was concerned that straight pipes along with secondaries removed would just be too loud and the x-pipe does have a resonating effect on tick over and low revs the system is quietish (apart from when cold)

I am very pleased with the results so far
 

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I fear there is a lot of confusing information being sent out on this subject!

X pipes do not replace anything for them to be effective. The only reason for them replacing anything, cats or resonators, in small cars is for sacrificial reasons - ie there is no room to add an x pipe without discarding something.

The original need for X pipes started with the H pipe. In fact it was put in to reduce noise! Check out the acoustic engineering on the subject - it is very complex. Also in race engines it is imperative to have the two pipes balanced at the high revs they work at. The H pipe was found to be inefficient, so the X pipe was introduced for two reasons: 1. it allowed scavenging (as mentioned above) explained as when one pipe has gas being forced out, the other due to the firing order, is empty, so the 'full' pipe sucks out any residual gas from the empty pipe that adds to the performance, and 2. It was found that two sets of gasses meeting precisely at an X has not only the scavenge effect but also a turbo effect on each other thus producing a speeded up flow of both gasses.

The whole subject of exhaust is pretty complex, especially when detailed calculations of scavenging and wave charging (mainly for diesels though) are required. It is a misconception that a straight through exhaust per se is best - yes for sound, but best performance requires restrictions of some degree.
 

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Discussion Starter #20
Wow,I think I now know everything about X-pipes:smile:
Thanks.
 
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