Officially Unofficial x-pipe thread

[bassphreek]

2.slowT asked, so I moved this thread.

man you are just twisting my words.

go do some more research before talking shit. an x-pipe on a big v8 is beneficial. but not on a turbocharged car, like the 2.7T.
And you say its beneficial before the turbo spool on the 2.7T. Have you driven the 2.7T? The K03's spool at about 1500rpms, very little pre-spool rpms for it to make any difference.

how am I twisting words? the original statement was that straight pipes in place of x-pipe on a dual exhaust car"provide better performance". This is not in anyway true. Most people, read dyno charts to find the max output. If that's how you read charts, then the x-pipe may provide no difference on a peak number. If you decide to actually read the graph, I would bet that you would find higher low RPM torque and hp as a direct result of an x-pipe. My statement was in direct reply to that comment. I would assume by your persistence that you agree with the decrease in performance, BUT YOU DON'T. You said that it makes no difference. Do you see where I am coming from?

There are 3 possible outcomes from x-pipe installation.
1: decreased performance
2: same performance
3: increased performance

I said that you would see outcome #2 or #3, depending, but NOT see outcome #1.

And about the research, find me the documentation that proves your theory. I have searched high and low and can't find anything about the performance changes in either direction based of an x-pipe on a turbocharged car. I would love to see it the results from both setups. I'm not talking about some runs on a dyno and numbers. I would like to see something with a control and all different variations tested to make logical conclusions about what makes it better and what doesn't. Step back and think about the millions of dollars that Audi put into RD when designing the 2.7T . Do you really, truly, honestly think they would include a part that decreases horsepower and fulfills no other function.

I own an '02 AR 2.7t 6MT. So, I have driven one...I drive one everyday. Do you launch your car @ 1500 RPM's? Do you actually skip your turbo lag all together? No, you don't. You use those low RPM's to get your car moving. Albeit a small part of the equation, you can't honestly say that it doesn't make a difference.

[doobiesdaddy]

This is the reason that the 2.7t has a true dual exhaust. Xpipe on 2.7t will hurt your performance because it will provide added constriction and resistance of exhaust gas flow.

[Daft]

Technically, any turbocharged engine will run optimal with zero exhaust.

The simple act of having an exhaust system installed will reduce power in some ways. The point is to find the balance between sound and power. This is often difficult for people to do especially with the kind of power that the 2.7T can produce. The other side of it is that we A6/allroad owners tend to enjoy the quieter exhaust system and want our cars to appear more luxurious than "boy-racerish".

In a past thread on this very topic I gave my opinion that skipping the X-pipe will allow for better exhaust gas velocity since there is less cavitation of the gasses as they collide in the X-pipe.

Currently, the A6/allroad has a center resonator/x-pipe from the factory where gasses collide and the resonant frequencies are muffled. I personally enjoy this feature and others who have tried to move away from it often revert back.

The real question here is: How much power is lost with the X-pipe?

If you choose an X-crossover style pipe like the ones that Magnaflow makes, you can reduce the resonant frequencies and minimize the power losses. In fact, there are claims that the design of the X-crossover pipe can somehow increase power. I have never seen any data to back this up, but I have to imagine that this claim is more directed at naturally aspirated engines that need a properly constructed exhaust system to create a good cylinder scavenging effect.

So in conclusion, I don't see a major issue with using an X-pipe but, I would be more apt to use an X-crossover versus a regular X-pipe. The bends in the X-crossover are less aggressive and the gasses are more exposed to each other for a higher level of noise canceling.

Here are example pics for those who have not seen these parts before:

Regular X-pipe:



X-crossover pipe:

[4ringAR]

Ok I thought the stock system was true dual, i just had another look and i saw there was an x-pipe. I never noticed that before. HOWEVER, you said that Audi wouldnt do that if it hurt performance, well lets not forget that this is a luxury cruiser we are talking about, not a performance oriented sports car. If you read that link you posted before, it says how an x-pipe quiets down the exhaust. A quiet exhaust is something Audi might have considered for this type of car when they decided to include an x-pipe. Neither of us designed the A6 or the 2.7t, so we cant have the final word on their reasoning for it.

Until you can prove than an x-pipe will actually IMPROVE performance on a turbocharged engine, I stand by my original words. I have seen many sources say that zero-backpressure is optimal on a turbocharged engine. Yes it(an x-pipe) is benefical on a n/a v8, not arguing that, but i disagree with your statement that it is benefical on a turbocharged car.

[Daft]

Ok I thought the stock system was true dual, i just had another look and i saw there was an x-pipe. I never noticed that before. HOWEVER, you said that Audi wouldnt do that if it hurt performance, well lets not forget that this is a luxury cruiser we are talking about, not a performance oriented sports car. If you read that link you posted before, it says how an x-pipe quiets down the exhaust. A quiet exhaust is something Audi might have considered for this type of car when they decided to include an x-pipe. Neither of us designed the A6 or the 2.7t, so we cant have the final word on their reasoning for it.

Until you can prove than an x-pipe will actually IMPROVE performance on a turbocharged engine, I stand by my original words. I have seen many sources say that zero-backpressure is optimal on a turbocharged engine. Yes it(an x-pipe) is benefical on a n/a v8, not arguing that, but i disagree with your statement that it is benefical on a turbocharged car.

I'll assume that you are addressing the OP of this thread but, I can definitely make the guess that Audi's main goal here was sound level suppression.

As we've both stated, the A6 is a luxury car and you can tell that Audi has always tried to mute/hide the evidence of a turbocharger and it's tell-tale signs. The boost is so low in stock form that you can't even hear the turbo's spool. Even the airbox is designed to remove all throaty-ness from the intake system.

While there is no direct proof that I have seen of an X-pipe making more power, there's no reason to state that it doesn't.

The fact of the matter is that when a tuning shop makes a top-end power setup, they employ the dual-exhaust approach first.

Aftermarket parts tuners like APR choose to use the center resonator/X-pipe because their target customer base will be happier with a throaty exhaust note at WOT while having no "fart-can" droning under cruising conditions.

[4ringAR]

yes, i was addressing the op. you squeezed in your post while i was typing.

[bassphreek]

I'm trying to sum up these replies in a tidy manner....bear with me.

I would be more apt to use an X-crossover versus a regular X-pipe. The bends in the X-crossover are less aggressive and the gasses are more exposed to each other for a higher level of noise canceling.

right off Magnaflow's page....right above your picutres.

The result is a significant increase in power and torque but a reduction in db sound levels...the best of both worlds.

followed by

Our X-Pipe transitions are available in 2.25" to 3" inlet/outlet diameters and can be found in many of our cat-back systems, or sold individually for those looking to complete their one-off system.

MagnaFlow's stainless steel Tru-X crossover pipe represents a significant leap forward in technology over traditional H-Pipes. The more gentle radius allows for better exhaust gas scavenging, noice cancellation.

The x-pipe is for the do-it-yourself'er and the crossover is to be used as a direct replacement an existing h-pipe where it will fit. They will both provide the same result. the actual inbound angle to the X is the same. It's more a matter of application.

but i disagree with your statement that it is benefical on a turbocharged car.

I didn't say it was beneficial....that's what I'm trying to get across. I said it's not detrimental. There is a big difference.

I can definitely make the guess that Audi's main goal here was sound level suppression

I don't often go out and say this about speculation, but...I 100% disagree with you on this. We already have 3 flipping mufflers....I don't think that they would have chosen an x-pipe for sound purposes.

The other thing you guys keep pushing is that this is a luxury car. Did they not put the same drivetrain and exhaust setup on a S4? I don't think a S4's primary goal to be luxury...

I will end with the official reproduction of my original statement:

A x-pipe will not decrease power.

[4ringAR]

no. the exhaust is very different on the S4. because the B5 chassis only has one exhaust opening it utilizes one pipe.
Quoting that stuff off of Magnaflows site....nobody is arguing that x-pipes are good for n/a v8's. what they posted on their site is to help drive sales, if it shows added power and torque on one application does not mean you will get the same results on every application out there.(chances are they tested it on a V8, the main target audience on their site is clearly muscle cars not turbo'd v6's.)
But if we are going to go quoteing magnaflow as the end-all, be-all source, lets not forget about what they also said in there "...but a reduction in db sound levels"
Yes, that means it makes the exhaust quieter, as I was saying earlier.
Why would Audi want it to be quieter? Because it is FUCKING LUXURY CAR. Most people that bought these cars new wanted a quiet car. The A4 is an entry level luxury car, the S4 is the same car in sport trim.

And there are not 3 mufflers. There is a resonator and a muffler on each side. The resonator contains 2 seperate chambers, one for each side, even though it is one unit. 2 mufflers per exhaust pipe is pretty standard.

[bassphreek]

I stand corrected on the S4. but....

...nobody is arguing that x-pipes are good for n/a v8's.

...Most people that bought these cars new wanted a quiet car. The A4 is an entry level luxury car, the S4 is the same car in sport trim.

First, as you keep bringing it up, when did I ever mention a v8?

And second...when did I mention anything about sound? My exact comment was about performance. In fact, I made further comments on how the sound is a preference, some will like it and some wont. I was not commenting on sound whatsoever....I was commenting on performance. ADDING A X-PIPE WILL NOT DECREASE PERFORMANCE. Wait, stop...go back to that last sentence and read it again, out loud!

BTW, I dare you to tell an S4 owner that he bought an A4 with sport trim. H could have saved his money and just bought an s-line..... A4 and S4 are not the same. Same chassis. Different car.

[4ringAR]

i keep bringing up the v8 because you seem convinced that the 2.7T will gain or not loose performance from x-pipes vs straight thru simply because thats how it works on a v8. that is why i keep bringing it up.

you didnt mention sound, I did. I said that the x-pipe is probably to keep noise levels down on the 2.7t, not for performance. and then you said that audi would sacrifice anything for performance on this car, which was obviously their halo sports car built for performance...

Same car, different trim level. its a B5 A4 with all the sport trimmings. aka, 2.7t, 6speed manual, different seats, brakes, and interior trim. Id say that YES it is still an A4 at the core if the vast majority of parts are interchangeable(doors, fenders, hood, head/taillights, trunk, etc etc.)

yes i have read that statement. you seem to have changed your stance. in your first post you said it will either gain or not change performance. i still believe that it will either not change performance or decrease performance, vs straight pipes.

[bassphreek]

v6, v8, straight-6, v-12....it doesn't matter what the source of power is. If you have a dual exhaust setup, a X-pipe will not harm performance.

I did imply that Audi would not sacrifice power for sound. They could have just as easily split the resonator and moved it upstream to remedy a sound problem. You don't add an x-pipe for sound reasons, its an added benefit of the performance.

How can you honestly say that an S4 is an A4 with all the trimmings. The first 3 of 4 things you listed (motor, trans, brakes) arent "trimmings". Trim levels include things like heated seats and navigation...not entire drivetrain and handling changes.

Finally, I have not changed my statement. If there three posibilities for outcomes (see my first post) and I choose #2 and #3, then I am not choosing #1. If I tell you that I like the weather to be below 80, you can come to the logical conclusion that I don't like weather warmer than 80. My statement that "it will either gain or not change performance" can be followed up with the logical conclusion that I believe that "it will not decrease." You have chosen #1 and #2, but not #3.

I think we both agree that there is a possible null change. When there is a change is where we differ, but I haven't found proof either way. Sooner or later, someone wlll come along with a really good set of test data and one of us will get to say "I told you so."

until then.......

[wofman]

Actually, I may have been mistaken on other post about Audi having "true" dual exhaust -- stock. But I don't think it's a real x-pipe -- more of an "h-pipe"? (for sound cancellation effects as exhaust follows path of least resistance) -- but pix here on forum look like not "true" dual either. I threw my stocks away, can't recall.

Milltek has something like that also -- also not an x and since that's what I run I guess I'm scooting under car tomorrow (that won't be pretty sight) to see if it's an h-pipe or what. Thought mine was straight dual, pipes just close together (attached for support). And APR catback is true dual.

And as Daft and 4ring have noted, exhaust collisions cannot help performance, in theory should have some adverse effect but it may be so minimal as to be negligible. Endee666 has not seen drop when he went with/without/with but does say he gets deeper sound with x-pipe on his custom set-up. So Bass, I'll vote 1.85. Close to 2. And yes, I think auto manufacturer would design exhaust with an "ear" toward sound -- esp if performance effect was negligible. Engineered aftermarket systems do not use x-pipes for turbos.

[audidub0490]

The X pipe will not hurt the cars performance in any way whatsoever.... the ONLY way it would kill performance is if the inner diameter of the X pipe was smaller than that of the pipe before it causing restricted flow and forcing the exhaust to slow down causing the pipes to "backup" in a sence slowing the turbos or raising the spool of them. YES having a straight pipe will increase performance only if you have no mufflers or resonators allowing the exhaust to flow freely with no opposition. the only reason that the X pipe does not decrease performance is because the turbos are forcing the exhaust out and all the piping is the same size. no restrictions other than mufflers and resonators. now yes the X pipe will create come back pressure but not enough to affect any forced induction engine turbo or supercharged the velocity is too high. with naturally aspirated motors you need back pressure to keep performance. if needed i can explain the use of back pressure in the motor. so having the X pipe in an NA motor will provide some of that back pressure to increase performance.

[Daft]

I'm not seeing what all the debate is about....

An X-pipe is primarily designed for N/A cars that need back pressure to help scavenge (aka. draw out) the spent exhaust gasses in the cylinder after ignition.

Our turbos already do this because the cycling of the turbine blade pushes out gasses while also drawing them out of the cylinders.

While our OEM exhaust systems have an X-pipe before the center resonator, it has to have been put there for noise canceling. Audi would not have added an X-pipe to create more power on a turbo car.

This all means that an X-pipe can create a small amount of slowing in the exhaust path and could also cause some power loss. How much? Not a whole lot.

Will you make more power without one? Probably?

How much more? Not a great deal, so little that it's hardly noticeable. In fact you'll loose more power from the exhaust bends and resonators than the one X-pipe.

If you wish to reduce the droning sound of the exhaust note, use an X-pipe.

If you are not concerned with that sound, leave it out.

I cannot see what else there is to discuss here......

[wofman]

The end.

[audidub0490]

amen

[bassphreek]

I can't figure out why you guys are obsessed with pairing a x-pipe to NA cars... You have to set aside the fact that there is a high use of them on NA cars because more NA cars use a true dual exhaust. It's like doing market research about flip-flops using Jamaicans and Canadians. Sure, Canadians wear flip-flops, but not nearly as much as Jamaicans do. Therefore, you will get many more examples from Jamaicans. Ok, enough with the analogies.

Forget the sound thing for 5 minutes and understand that its a side effect of installing a x-pipe.

A x-pipe is applicable to ANYTHING with dual exhaust. Do you guys believe that equal length headers make a difference? If you do, then you have conflicting views on 2 things that have the same primary purpose....increased power. The scavenging effect does not cause power loss.

I understand that the turbo creates some backpressure. The benefit of having a x-pipe on a twin turbo system is that the scavenging (instead of relieving pressure directly from the cylinder head) can help pull the gases from the backside of those turbos and keep the spool up. A turbo doesn't pull gas thru or push it out, it get spooled by the pressure created on the front side. You have to have pressure on the front to move it thru, the turbo has no hand in making this happen. Where do you think turbo lag comes from? You have to get X lbs of pressure forced thru to make it work. Although minimized, there is still an exhaust pulse thru the turbo. That means that there is a time where there is less velocity in side 1 and the current velocity in side 2 helps move it out. If your turbos turned your exhaust into a constant whirring gas stream by "pulling it thru" when its spooled then your car would have no vroom sound. There would be no growl...it would be a seamless, eerie sound. It would sound like a Tesla. If all the exhaust gas was actually used in the spool, it would have a perfect efficiency. But it doesn't, there is friction. The friction will always cause gas to get thru that hasn't "helped out.' Because of this, your car exhaust has a partial identity to that of a naturally aspirated exhaust. I will admit it is very small percentage of the total picture, but it IS there. Because it is there, you will get performance benefits from the x-pipe.

Does this make sense to anyone?

[wofman]

I can't figure out why you guys are obsessed with pairing a x-pipe to NA cars... You have to set aside the fact that there is a high use of them on NA cars because more NA cars use a true dual exhaust. It's like doing market research about flip-flops using Jamaicans and Canadians. Sure, Canadians wear flip-flops, but not nearly as much as Jamaicans do. Therefore, you will get many more examples from Jamaicans. Ok, enough with the analogies.

Forget the sound thing for 5 minutes and understand that its a side effect of installing a x-pipe.

A x-pipe is applicable to ANYTHING with dual exhaust. Do you guys believe that equal length headers make a difference? If you do, then you have conflicting views on 2 things that have the same primary purpose....increased power. The scavenging effect does not cause power loss.

I understand that the turbo creates some backpressure. The benefit of having a x-pipe on a twin turbo system is that the scavenging (instead of relieving pressure directly from the cylinder head) can help pull the gases from the backside of those turbos and keep the spool up. A turbo doesn't pull gas thru or push it out, it get spooled by the pressure created on the front side. You have to have pressure on the front to move it thru, the turbo has no hand in making this happen. Where do you think turbo lag comes from? You have to get X lbs of pressure forced thru to make it work. Although minimized, there is still an exhaust pulse thru the turbo. That means that there is a time where there is less velocity in side 1 and the current velocity in side 2 helps move it out. If your turbos turned your exhaust into a constant whirring gas stream by "pulling it thru" when its spooled then your car would have no vroom sound. There would be no growl...it would be a seamless, eerie sound. It would sound like a Tesla. If all the exhaust gas was actually used in the spool, it would have a perfect efficiency. But it doesn't, there is friction. The friction will always cause gas to get thru that hasn't "helped out.' Because of this, your car exhaust has a partial identity to that of a naturally aspirated exhaust. I will admit it is very small percentage of the total picture, but it IS there. Because it is there, you will get performance benefits from the x-pipe.

Does this make sense to anyone?

You think others are obsessed?
(And no, I don't think you have it right if that is what you mean by "makes sense" -- no scavenging takes place downstream of turbine, back pressure is bad for turbo exhaust, x-pipes don't increase velocity)

I'm done, no matter what you post (again)

[doobiesdaddy]

Who the hell is this fuckin noob?

Warren: he gives Jersey a bad name

[bassphreek]

Who the hell is this fuckin noob?

Warren: he gives Jersey a bad name

I'll just let everyone take their misconceptions and misinformation and run to the hills with it. You guys take what you read in forums as the holy word. Most people read about results, have no understanding about how things actually work and got those results, pay someone to install it to their car, and then consider themselves an expert.

This whole things started by someone saying not to install a x-pipe because straight pipes "provide more power". This is absolutely not correct.

And thank you doobiesdaddy for settling my misconception that I had coming from VWVortex. I figured that when I moved to the Audizine forums that I wouldn't encounter slobbering tools. Guess I was wrong, you seem to be as genuine as the bulk of the 17 year olds in MK4 forum. Congratulations.

[Daft]

This whole things started by someone saying not to install a x-pipe because straight pipes "provide more power". This is absolutely not correct.

Until you show me proof that an X-pipe creates more power on a turbocharged application, you are doing nothing more than stamping your feet and acting rediculous.

I am the one who said that straight pipes will make more power. Why you ask?

Well lets do this all again shall we?

To save time, here is what I posted back in October last year in this thread:

__________________________________________________ __________________________________________________ _________
In an ideal case for peak power you would want both exhaust paths to be completely separate.

You really won't have any benefit from creating a location for gases to collide and slow down. The primary function you need is consistent exhaust gas velocity. The faster the gasses leave the pipe, the easier it is on the motor to perform its combustion process.

Since you have turbos, the turbine wheels will cause exhuast gasses to leave the combustion chamber but, once they are out, they need to travel quickly and smoothly as they cool and slow down.

Have you ever run the car with no cat back? It's got alot of extra power. Why? Because the exhaust gasses create no resistance on the turbine wheel and the turbine can turn much easier (less lag and more top end flow).

If I were building a high performance exhaust system, I'd make sure it met the following criteria:

1. Large enough inner diameter to flow the level of gasses I will be passing through it.
2. Least amount of bends possible and mandrel bent to promote less resistance.
3. No X-pipes or X-resonators to keep velocity at maximum levels.
4. Low resistance mufflers to not slow gasses at the exit point. Resonator type not baffle type.


This will not result in a quiet exhaust setup but, it will make the most power without running open pipe.

As another option, you could install dump pipes that open only under WOT and have a switchable max-power option. Dumps are cool but, very loud as they are essentially open downpipes under WOT.

__________________________________________________ __________________________________________________ ___

Honestly, this is common sense here. If a turbo setup makes optimal power on open downpipes, how can any exhaust, let alone cross-mixed and bent pipes create more power?

Colliding exhaust gasses will never promote or create better velocity in the exhuast piping than a turbine. The turbine is pushing and pulling the gasses out of the cylinders. The actions in the pipes after the turbine are only going to decrease that effect. We don't need any extra back pressure here.

In conclusion, you will make:

1. More top-end flow
2. More power
3. Rev faster

with less restriction and collisions in the exhaust piping on a turbocharged setup.

[chrisbostonusmc]

I have an X pipe

No I really do! but at 24psi I have alot more to worry about than exhausts

water meth, bigger headgasket, IATs results etc

[wofman]

I'll just let everyone take their misconceptions and misinformation and run to the hills with it. You guys take what you read in forums as the holy word. Most people read about results, have no understanding ... and then consider themselves an expert.
This whole things started by someone saying not to install a x-pipe because straight pipes "provide more power". This is absolutely not correct.....

So I come back to site today, and this continues.



"It ain't what he don't know, it's what he knows that ain't so."
Will Rogers (actually pretty much plagiarized from Mark Twain)

As for NJ -- you gotta problem wit dat? Fuggedaboudit.

wofman

[ENDEE666]

I was VERY hesitant to chime in here. This should put this to bed. I ran 11.8 with an X/crossover pipe and 4 mufflers. That time has yet to be beaten by another A6. So yeah, that X pipe must be costing me at least 100+whp huh??

Yes, they are more beneficial (performance wise) on an N/A car, but they do not hurt a boosted car by much more than a few hp, and they do alter the sound. I removed mine, did not feel any increse in power, possibly a slight loss when the turbos kicked in, but no significant change. I did not like the sound without it as much as with it. I put it right back on. My opinion, my preference.

I can assure you that it will not be the deciding factor in winning or losing many races... Worry about the rest of the car & setup and let the X pipe thing go. If you like them, use them. If you do not, DON'T... Now move on.

[RS6-4dr911]

Just for fun, I'll weigh in. Having read through this, I don't believe anyone's exactly on track here, but Bassphreek is close. First Daft is grossly incorrect (someone tried to point this out) that a turbo helps extract exhaust. The turbine blades are an obstruction to flow, not an enhancer. The only way they would be is right at throttle lift and the turbos continue to spin, but at that point, you're not really trying to develop power.

The x-pipe, as I understand it, was originally developed (in the sixties IIRC) to smooth out the exhaust pulses between cylinder banks. At the instant one side exhausts, the other side isn't. By having the x-pipe shortly after the header collector, the high pressure in one side can "escape" to the other, effectively in-between the pulses from the receiving side. Engines like a little back pressure to develop lower end torque and the headers do this, but once past the collector, you'd like as little back pressure as possible - the x-pipe helps this.

The reason they have little effect on a turbo engine is because the pulses are effectively eliminated as they pass through the turbine blades. This is not the case with a driven supercharger (roots type, belt driven, etc) since there is nothing downstream of the exhaust valve to smooth the flow.

The x-pipe doesn't really cause the gases to collide so much as blend. Why Audi put the x-pipe we can only speculate but it's hard to imagine that it could do anything but help.

[doobiesdaddy]

Why Audi put the x-pipe we can only speculate but it's hard to imagine that it could do anything but help.

You are confused. Audi did not put an xpipe on the 2.7t exhaust (allroad I know as a fact, s4 and a6 might be different). The OEM resonator is 1 unit that both pipes pass through. Both pipes are independent the whole way through the resonator. The gases never meet. What goes in one side goes out the other without any x pipe or merging of gasses or flow. I know this because I cut open my resonator with a blow torch and looked at it after I removed it from my car after installing my aftermarket exhaust. Definitely 2 independent exhaust paths from turbo to muffler with no xpipe.

[chrisbostonusmc]

I was VERY hesitant to chime in here. This should put this to bed. I ran 11.8 with an X/crossover pipe and 4 mufflers. That time has yet to be beaten by another A6. So yeah, that X pipe must be costing me at least 100+whp huh??

Yes, they are more beneficial (performance wise) on an N/A car, but they do not hurt a boosted car by much more than a few hp, and they do alter the sound. I removed mine, did not feel any increse in power, possibly a slight loss when the turbos kicked in, but no significant change. I did not like the sound without it as much as with it. I put it right back on. My opinion, my preference.

I can assure you that it will not be the deciding factor in winning or losing many races... Worry about the rest of the car & setup and let the X pipe thing go. If you like them, use them. If you do not, DON'T... Now move on.

+100000


P.S.- we'll see what happens when I get back from Japan and I run the E85 file Nick!

[wofman]

Just for fun, I'll weigh in. Having read through this, I don't believe anyone's exactly on track here, but Bassphreek is close. First Daft is grossly incorrect (someone tried to point this out) that a turbo helps extract exhaust. The turbine blades are an obstruction to flow, not an enhancer. ... Engines like a little back pressure ....The x-pipe doesn't really cause the gases to collide so much as blend. Why Audi put the x-pipe we can only speculate but it's hard to imagine that it could do anything but help.

ding! ding! ding! We have a winner!
Most misinformation, myths, gibberish on any one post on this thread! (Nice car, though)
Daft -- you better return your engineering diploma, silly man. What were you thinking?


I fear we have another thread likely to go pictoral.



wofman

[bassphreek]

Thank you Endee666, RS6-4dr911, and chrisbostonusmc! I thought I was the only sane person around here for a minute.

I got pushed back onto my heals that straight pipes bring more power than x-pipe. It took Endee, who had been referenced several times, to chime in and help confirm my thoughts.

And RS6-4dr911, you beautifully summed up what I was trying to say thru my moments of frustrations while typing replies.

doobiesdaddy. check again. it's not as glamorous as the magnaflow's, but its located midway between the cats and resonator. reach under there and you will feel the connection between them.

[4ringAR]

nobody said that x-pipe vs straight pipes was going to result in the gain/loss of 100whp. whether or not it gains you .5hp or 1000hp is not the issue, what we are trying to prove(one way or another) is that one way or the other is the "better" way.

RS6-4dr911, you were spot on and then you said the turbines from the turbos smooth out the flow. That is why an x-pipe is unnecessary on the 2.7t. The turbines are fullfilling the job of the xpipe by evening out the flow and providing backpressure.

I just dont understand why you think backpressure = power. Why do people put larger diameter exhausts on their car? To free up backpressure and create more power.

[Daft]

First Daft is grossly incorrect (someone tried to point this out) that a turbo helps extract exhaust. The turbine blades are an obstruction to flow, not an enhancer. The only way they would be is right at throttle lift and the turbos continue to spin, but at that point, you're not really trying to develop power.

Actually, there's more to it than that.

You see, when the combustion process occurs cylinder pressures can easily exceed twice the pressure of the gasses remaining in the exhaust manifold. At the very moment that the exhaust valves open, you will overcome the back pressure that the turbine wheel would normally create.

Once the cylinder pressure has dropped below the pressure in the manifold, you could then encounter a negative effect from the turbine wheel's back pressure. The catch here is that the turbine wheel is still spinning because other exhaust pulses are still pushing it. So, under acceleration this is not an issue.

Also, let's be realistic here. It's not like the turbine wheel is some sort of brick wall that robs the engine of power. There is an initial amount of inertia that must be overcome to spin the turbine wheel up to the desired speed but, that resistance drops down to a much smaller level once it is already spinning. So when you begin to spin up the turbine to a specific level, you are expending some energy but, it will not be at that same level once you achieve full boost.

The amount of time to raise boost to max pressure is very brief even on even a K04 equipped car and then you are just using the wastegate to maintain turbine speed at that point.

Grossly incorrect....


As for the rest of the nonsense in thread, I never said that an X-pipe would cause a tremendous loss in power. I said it would be a small one at best but, it would still be a loss.

Velocity is velocity. If there is a component that causes a decrease in velocity, you are creating some added back pressure.

[wofman]

Thank you Endee666, RS6-4dr911, and chrisbostonusmc! I thought I was the only sane person around here for a minute.
I got pushed back onto my heals that straight pipes bring more power than x-pipe. It took Endee, who had been referenced several times, to chime in and help confirm my thoughts.
And RS6-4dr911, you beautifully summed up what I was trying to say thru my moments of frustrations while typing replies.

Your "sanity" claim seems premature, since you clearly did not comprehend what Endeee wrote:

Yes, they are more beneficial (performance wise) on an N/A car, but they do not hurt a boosted car by much more than a few hp, and they do alter the sound. I can assure you that it will not be the deciding factor in winning or losing many races... Worry about the rest of the car & setup and let the X pipe thing go. If you like them, use them. If you do not, DON'T... Now move on.

Chris didn't support you either, just that he, like Endee, has bigger fish to fry with his set-up than worrying about minor effect of power loss from x-pipes. That was his implicit point.

And 4dr911 has absolutely no clue. Nice car, though.

As Daft and I have been telling you, obstruction is bad, free flow is good, x-pipes cannot help velocity:

...skipping the X-pipe will allow for better exhaust gas velocity since there is less cavitation of the gasses as they collide in the X-pipe.
The real question here is: How much power is lost with the X-pipe?

Probably not much.

The only reason for x-pipe is sound wave cancellation.

[bassphreek]

My originial comment was that the x-pipe will not cause power loss... Endee said the exact same thing as proven thru his trials and experience. I admitted that I was unsure of increases on a turbocharged engine, but hold strong in my statement that it will not cause loss. The x-pipe scavenges the exhaust before it and keeps balanced pressures after it. It doesn't created backpressure, it assists in the removal of it.

Do you really think that the only purpose of a x-pipe is noise cancellation?

And speaking of bigger fish to fry, I'm done with this.

[4ringAR]

On the A6, yes. I think that very well could be its sole purpose. It is a cheap way to keep noise levels/raspiness down.
Look at this post/listen to these videos. I understand this isnt stock exhaust vs stock exhaust sans x-pipe, but it shows what an xpipe does to sound(quiets it down).
http://www.audizine.com/forum/showthread.php?t=296610

[wofman]

My originial comment was that the x-pipe will not cause power loss... Endee said the exact same thing as proven thru his trials and experience. I admitted that I was unsure of increases on a turbocharged engine, but hold strong in my statement that it will not cause loss. The x-pipe scavenges the exhaust before it and keeps balanced pressures after it. It doesn't created backpressure, it assists in the removal of it.

Do you really thinkg that the only purpose of a x-pipe is noise cancellation? WOW

No doubt you "hold strong" -- simple principles be damned, you are resolute. You said it increased performance. It doesn't. As explained by Endee and Daft, the harm is minor. You don't understand "scavenging" even though I PMd you an article by Garrett engineer explaining there is no scavenging after the turbines on turbo systems. You don't understand difference between n/a and turbo.

Yes the only constructive effect on Audi 2.7 is sound effects -- ear of beholder, however. Engineered aftermarket performance systems don't use them. WOW that.

[bassphreek]

No doubt you "hold strong" -- simple principles be damned, you are resolute. You said it increased performance. It doesn't. As explained by Endee and Daft, the harm is minor. You don't understand "scavenging" even though I PMd you an article by Garrett engineer explaining there is no scavenging after the turbines on turbo systems. You don't understand difference between n/a and turbo.

Yes the only constructive effect on Audi 2.7 is sound effects -- ear of beholder, however. Engineered aftermarket performance systems don't use them. WOW that.

I never said it increased performance. I said that it didn't decrease....understand the difference.

I have read that article in several locations. The problem with using it as an example is that it speaks of a singular turbo to a singular exhaust. The item at hand involves 2 turbos and 2 exhaust pipes. The x-pipe brings them together for higher exhausting efficiency.

As for performance exhausts not using them.....look again.

[wofman]

Helloooo. You first claimed that x-pipe "will reduce the back-pressure and improve performance. Don't get me wrong, you could reduce the back-pressure too much and actually make it worse, but in general they will improve performance."

You then said "I would bet that you would find higher low RPM torque and hp as a direct result of an x-pipe." Later modified to "same" or "increased performance", now down to "didn't decrease" -- but with more recent elaboration that "the x-pipe brings them (exhaust streams) together for higher exhausting efficiency".

But you never said increased performance? Oh.

Milltek (which I use) is designed with piping through same routing/location as stock piping, and it is not an x-pipe you (almost) see in picture you posted. Blow it up and you'll see better. APR also doesn't use one.

[doobiesdaddy]

doobiesdaddy. check again. it's not as glamorous as the magnaflow's, but its located midway between the cats and resonator. reach under there and you will feel the connection between them.

Midway between the cats and the resonator is nothing but straight pipe on the OEM exhaust 2.7t allroad.
And Magnaflows??? WTF are you talking about?

[Stampy]

Holy crap I didn't know this thread was so intense. I've seen two of my previous pics posted already.

I removed my Center resonator and had no difference in power or sound....with everything else stock on the exhaust. When I went straight pipe, it was obnoxious loud and I felt a power drop off. Not sure how this would help the thread, but figured I would add it.

[ENDEE666]

Not sure how this would help the thread.

Lol, nothing is going to help this thread at this point. Too many people feel their opinions are more accurate than proven facts...

I thought my ending statement was enough-> "If you like them, use one, if you do not, DON'T"... But apparently not.

Anyone who feels that strongly about proving their point, simply back it up with proof & documentation. Buy an X pipe, install it, dyno the car. Remove it, dyno again. Make sure all other variables like ambient temp, engine temp, IAT's, etc do not change. If at that point you see something worth talking about, share it. Until then, I think there is nothing left to do but stamp your feet claiming you know something that you can not back up or document.