x-pipe / h-pipe

[ranksie]

Do you mind me asking what its cost to have your work done, and was it worth paying the extra? (hey, you should be on commision with AAS)

[aidanjaye]

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.

So where is the stock exhaust linked?? I've just had a look and can't see any link pipe, only the resonator box (which doesn't seem to be linked).

[RS4POWER]

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.

So where is the stock exhaust linked?? I've just had a look and can't see any link pipe, only the resonator box (which doesn't seem to be linked).

Same location as the mtm setup in photo below. I saw it while I was under a stock car a few months ago. It was a little smaller than the MTM obviously since the stocker is a smaller diameter.

[aidanjaye]

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.

So where is the stock exhaust linked?? I've just had a look and can't see any link pipe, only the resonator box (which doesn't seem to be linked).

Same location as the mtm setup in photo below. I saw it while I was under a stock car a few months ago. It was a little smaller than the MTM obviously since the stocker is a smaller diameter.

Is it?? I had a look and also checked lower photos from Audi docs and its not shown.

[aidanjaye]

Standard pipes don't join (left and rightbank) apart from a mounting plate until both pipes enter the center resonator. There is no link pipe.

Following from Audi service training manual (which Ishould have looked at first).

" the front silencer for each exhaust pipe is housed in a common casing. However, the exhaust pipes are kept seperate."


So, maybe the cars on standard maps are set up to run seperate exhaust routing, hence unless remapped, x-pipes and h-pipes can cause a slight degrease in flow (as milltek found).
Obviously once remapped, the lodgic is out the window.

[RS4POWER]

Standard pipes don't join (left and rightbank) apart from a mounting plate until both pipes enter the center resonator. There is no link pipe.

Following from Audi service training manual (which Ishould have looked at first).

" the front silencer for each exhaust pipe is housed in a common casing. However, the exhaust pipes are kept seperate."


So, maybe the cars on standard maps are set up to run seperate exhaust routing, hence unless remapped, x-pipes and h-pipes can cause a slight degrease in flow (as milltek found).
Obviously once remapped, the lodgic is out the window.

I stand corrected!

I saw the setup from the distance and thought it was an H but from the photo below (another setup) it appears to be a bracket.

[R7ANO]

So makes me wonder why Audi didn't join it as it would have been easy!?
it must be something to do with limiting the torgue?
I don't no why they needed to limit it but they limit it with the throttle map and TC as well?
It may be down to stopping wheel spin!

[RS4POWER]

The torque limiter is controlled by throttle valve angle in 1-3rd gear up to 5.5k rpm. It will then open 100% which is why we feel that pronounced kick (especially in cool temps).

[R7ANO]

Yes that's right, the exhaust may also be part of the torque limiting package?

[P_G]

Do you mind me asking what its cost to have your work done, and was it worth paying the extra? (hey, you should be on commision with AAS)

Stuart has done a lot of work for me over the years so I am happy to recommend To have an x-pipe installed IIRC is about £300 and a half day's work. I then had the back boxes and pipes done. I sourced a secoind hand OEM RS4 cat back system, and Stuart removed the valves and tip from it and wleded them to freer flowing and lighter back boxes with 2.5" pipes and connected that to the x-pipe. Cost for that part was £6-700 last year. so approx £1K including RS4 exhaust for a non res. valved system and 1 day's worth of work.

ranksie, if you PM before you are due to AAS I'll pop along and you can hear the system to see if you want to further modify at a later date


And aiden is right, the OEM system is not h-pipe linked, just held together by the bracket over the mid silencers. Straight pipe production is cheaper than h- or x-pipe production. As said, I have not lost any power with my set up at either stage unlike Milltek's results. Sane happened on the B6 S4, they could only use an h-pipe on their system as the x-pipe did not work but the AAS one did work.

Part of it though is dependent on pipe size used. If I used 3" pipes then it probably would lose power.