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Just a quick question ... do you require some sort of link pipe on exhaust system between the left and right.
All manufactures seem to have (cross pipe / h-pipe / x-pipe).
Is this to balance the exhaust pulses?

and there was me thinking it was just for rigidity in the structure

Hi,

I has an x-pipe fitted to my S4 by AAS is newcastle and it made a noticable difference.

Check out this link which explains the difference between an h and x-pipe.

http://www.streetdirectory.com/travel_g ... power.html

Regards, Chris.

Something to do with scavanging the exhaust gases and improving exit flow. I'm sure there is a more technical explanation floating around somewhere.

I think I misunderstood the bit you were talking about

Ice_Coffee wrote:I think I misunderstood the bit you were talking about

Which bit??

Basically planning on dumping the centre resenator and most options for replacements have a link pipe joining the left and right hand exhausts banks of the engine (ala Bora, Supersprint and ECS)
Now from the brief explanation above (cheers), seems that the cross over quietens the exhaust and slightly alters the power.
Initial question is - if I get my local fabricator to fit pipes in place of resonator - does he need to join these by a link pipe. I am retaining the remainder of the standard exhaust along with the valves so noise, when valves are closed shouldn't be an issue. Therefore does it warrant going to the hassle to link the pipes.

Read somewhere that Milltek messed around with various link pipes and some actually reduced power. Surely the quickest way out with no obstructions should be the best.

There is a physics description for the effect although I can't remember what it is called, something along the lines if you have two pipes with gas flowing in one dircetion, by linking the two with a section that section creates a kind of vacuum which pulls the gases in addiiton the the forced expulsion and increases the rate of expulsion after the section as well, so increasing the rate of flow (scavanging).

Hence why it pops and burbles when you lift off / aren't forcing gases through and the air / gas pressure is reversed.

Something along those lines anyway. It gets louder because you are taking the silencers away and an x-pipe will scavange better.

Fast moving air is at a lower pressure than air at a slower speed, so the exhaust gases flowing through one side of the x-pipe suck air out of the other pipe, creating a vacuum and sucking air out of the cylinder(s) on the other bank which have their exhaust valve still open.

This effect doesn't work well with h-pipes, hence why the x-pipe was developed.

Regards, Chris.

This is my theory, Not sure if its right but just thinking logically!
I'm sure the standard exhaust is not linked,
Linking it with a H or X pipe will give the engine more torque IF its been Mapped for it.
Thats why all aftermarket systems have the link pipe in to show that they are an improvement over stock,
The RS4 is mapped and timed (cam timing & overlap) to work with the stock exhaust this maybe be why people feel that a milltek (with a H pipe) without a map feels slower,I think Audi would have put a link in it if it was better as the pipes run together.
I have gone from a miltek back to stock as it was too loud for me, but now feel the car work better.
Doug at MRC may have a better view on this? it maybe something to do with regulations?

Milltek said the X pipe did not work for them when developing the exhaust. It lost power. The H pipe is more for getting rid of drone and any resonance.

R7ANO wrote:This is my theory, Not sure if its right but just thinking logically!
I'm sure the standard exhaust is not linked,
Linking it with a H or X pipe will give the engine more torque IF its been Mapped for it.
Thats why all aftermarket systems have the link pipe in to show that they are an improvement over stock,
The RS4 is mapped and timed (cam timing & overlap) to work with the stock exhaust this maybe be why people feel that a milltek (with a H pipe) without a map feels slower,I think Audi would have put a link in it if it was better as the pipes run together.
I have gone from a miltek back to stock as it was too loud for me, but now feel the car work better.
Doug at MRC may have a better view on this? it maybe something to do with regulations?

Stock exhaust does have an H-pipe.

The only after market exhaust without a link (that I know of) is the capristo. I am talking to capristo about this right now and they will do some testing with an x-pipe and get back to me.

The h/x will help balance the exhaust gas pulsing, maximize resonant scavenging and will increase piston velocity (if going from true duals to x/h). If you are after performance an x or h should be on your setup.

R7ANO wrote:This is my theory, Not sure if its right but just thinking logically!
I'm sure the standard exhaust is not linked,
Linking it with a H or X pipe will give the engine more torque IF its been Mapped for it.
Thats why all aftermarket systems have the link pipe in to show that they are an improvement over stock,
The RS4 is mapped and timed (cam timing & overlap) to work with the stock exhaust this maybe be why people feel that a milltek (with a H pipe) without a map feels slower,I think Audi would have put a link in it if it was better as the pipes run together.
I have gone from a miltek back to stock as it was too loud for me, but now feel the car work better.
Doug at MRC may have a better view on this? it maybe something to do with regulations?

I wasn't sure if the standard exhaust was linked within the resonator box?
Anyway, if Doug from MRC says that the link (H or X) is basically to reduce the drone at low revs, then thats fair enough for me. As I said, I'm keeping the rest (incl valves) standard so the noise shouldn't be "too" loud. Well thats what I'm telling the wife.

I can honestly say that the x-pipe on my car has not robbed any power and did not do so on my B6 S4 on OEM maps.

P G - I have booked my car in with the guys at Newcastle for next month. What should I expect in terms of power and just as importantly noise?

No real power gains I would say, possibly a few hp at best because you still have the stock rear silencers. Closed valves will sound like sport mode now and open valves a bit louder if just an x-pipe.