I think I've found it... source of late boost problems

[A4 Moda]

No really though. I've got my flame suit on. Believe me, I'm beating myself up right now.

I found the source of my late boost.

Recap: 71R Eliminator. I'm reaching full spool 20 psi at 4800rpms or 50000rpms, and sometimes later. I've checked every possible thing that I could with my setup. But I've boiled it down to this.

Yeah get ready for it....






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...












A little while back, I put on my stock exhaust system because I'm getting too old. The drone city and rasp riding was getting to my head. I might have gotten a few nosebleeds from the sound after I got home as well.

But i'm going to bet myself a dime that if I cut off the stock exhaust my late boost problem will be solved, and my car will be boosting normally.

Also, this meant that I had to turn down the boost and drive with no timing advancement either because my logs were showing CFs in the 6+ range and EGTs through the roof.

Who's in on the bet with me?

[Groove1797]

50,000 RPM's! DAMMMMM

[A4 Moda]

Yeah it takes a while to build up to 50,000 rpms.
Usually by the next lunar cycle I'm getting close.

50,000 RPM's! DAMMMMM

[absolutegtr]

Perhaps.....I dunno though full spool at almost 5K is quite alot...

what channel do you log for EGT's?

[A4 Moda]

Channel 34

[B6Lovin]

only one way to find out.... when you say stock exhaust - do you mean the cat too?

[doublezero30]

woah wait...stock exhaust with a big turbo? doesnt seem like a good idea to me...but thats beside the point. im unsure why you didnt just resonate your aftermarket exhaust more. i had custom 2.5inch system with 2 magnaflow resonators and magnaflow mufflers and it was almost silent until i decided to run a test pipe.

[7speed]

did you get the wastegate and did you try it ?

[A4 Moda]

No Cat. Just Stock Mufflers.

Resonators might kill some of the Rasp, but the drone increases. I need another muffler in the center there if I"m going to do another exhaust kit. I really don't want to though considering I've gone through about 16 exhaust setups in the past 6 years. It's a pain in the ass I can assure you.

7 Speed is the Man. Yes I got your wastegate. I haven't had a chance to try it though.

[A4 Moda]

Question is though. Do you think this would cause late spool? Everyone?

[Maverick]

maybe get a universal mufflers with 4" tips and some silencers?

[AudiA4_20T]

Question is though. Do you think this would cause late spool? Everyone?

YES, that isnt even a question... Its all about flow and your choking the shit out of that turbo with the stock exhaust

[A4 Moda]

There it is. I'm glad I finally found the damn problem. I thought I was losing my mind going over this problem for the past few months trying to diagnose the cause.

YES, that isnt even a question... Its all about flow and your choking the shit out of that turbo with the stock exhaust

[sean1.8t]

YES, that isnt even a question... Its all about flow and your choking the shit out of that turbo with the stock exhaust

x2!

i can't believe it took someone this long to post this.

the slightest bit of hinderence in flow will make quite a difference in boost treshold

[A4 Moda]

Like I said. I've been an idiot about it. The answer was staring me in the face and I didn't even have the hindsight to see it.

I'm going to get a quiet and free flowing exhaust in the coming weeks.

I'll post my results once that is completed.

x2!

i can't believe it took someone this long to post this.

the slightest bit of hinderence in flow will make quite a difference in boost treshold

[diagnosticator]

Question is though. Do you think this would cause late spool? Everyone?

No. The increased back pressure doesn't exist until the turbo has developed about stock boost, and higher. Before the turbo spools up, there is not much exhaust flow, (compared to open throttle with the boost) so there must be something else causing the problem.
How high is the boost when the high cat exhaust temps, EGT(not,) and 6+ timing retard?

[A4 Moda]

On optimal configuration, my boost would be 20 psi -22psi by 3800 rpm. 4000 rpm max on a hot day.

But as you understand, now it's at least 1000rpms later than that. sometimes reaching 6K before I hit 20psi.

Another point of reference. I used to hit 10psi at 3K rpms and on up very quickly.

Now At 3K i'm at 5psi on the dot.

What are you thinking john?

No. The increased back pressure doesn't exist until the turbo has developed about stock boost, and higher. Before the turbo spools up, there is not much exhaust flow, (compared to open throttle with the boost) so there must be something else causing the problem.
How high is the boost when the high cat exhaust temps, EGT(not,) and 6+ timing retard?

[20vturbo]

No Cat. Just Stock Mufflers.

Resonators might kill some of the Rasp, but the drone increases. I need another muffler in the center there if I"m going to do another exhaust kit. I really don't want to though considering I've gone through about 16 exhaust setups in the past 6 years. It's a pain in the ass I can assure you.

7 Speed is the Man. Yes I got your wastegate. I haven't had a chance to try it though.

therenis a borla muffler that fits in the center 3" in 2 2.5 out and they have it in diff sizes That made mine quieter..I have a 3" custom made exhaust with a cat, resonator , 1 center muffler and 2 rear mufflers It's ok but still screams when I open up, I guess that's the price to pay for 3"

[sean1.8t]

No. The increased back pressure doesn't exist until the turbo has developed about stock boost, and higher. Before the turbo spools up, there is not much exhaust flow, (compared to open throttle with the boost) so there must be something else causing the problem.
How high is the boost when the high cat exhaust temps, EGT(not,) and 6+ timing retard?

really though? i know you're a smart guy and all. but i think you're really just basing this off of calculations and whats on paper.

what real world experience are you basing this off of?

[RLB6]

I'm gonna say it again....Check your DV.

[B6Lovin]

this thread is kinda aggervating... OP - people are giving you advice, but based on the limited info we have about your car and the rest of your setup, the best and ONLY way that you'll figure this out is to set some time aside and just check over all the little things FIRST.

it's been suggested a few times to try swapping out your DV to see if maybe that's cause, i'd honestly begin with that to save you the trouble of waiting for an exhaust that might end up being too loud for you... only to find out that may not have been the cause (or atleast ALL of the cause) of your late spool. you've got a test pipe, so you're not hitting a wall as soon as exhaust exits the turbo, so you've got SOMETHING right.

do you have optimal flow? no. you dont. do you want a temporary way to find out if that's the problem?? unbolt your exhaust at the test pipe and take it for a spin. it'll be loud as fuck - but you'll find out if that's the problem.

all im saying is quit guessing and go try to fix it.

[mtbrider]

Thoroughly check your manifold, it may be cracked.

[diagnosticator]

really though? i know you're a smart guy and all. but i think you're really just basing this off of calculations and whats on paper.

what real world experience are you basing this off of?

I'm basing my comments on my intuitive understanding of how the components interact together, considered as sub parts of the engines operational parameters overall. My background is based on real world experience with operating, tuning and building real engines of all sizes. My experience includes some theoretical math based design training, but I'm mainly experienced with the hardware and hands on aspects.

Specific to your question here, I can't site a certain example directly, off hand, to validate and support my comments, except to say that my comments are based on my interpretation of the functional details existing with the subject discussion and the relevent technical facts involved.
A detailed explanation supported by reference to established technical principles can be provided for the concepts and conclusions that I am commenting about. Any opposing viewpoints should be evaluated usinjg the same scheme of accountability for accuracy and relevance to the issue discussed.

(fwiw, it took me over an hour to compose this reply, and that is often the case with other posts also. And that is maybe why my writing style is frequently as wordy and formal, not casual. It's hard to relate technical stuff, with a brief spontainious casual style, I don't know how to do that. I took English Comp 101 four times, never did pass that damn course. )

[sean1.8t]

I'm basing my comments on my intuitive understanding of how the components interact together, considered as sub parts of the engines operational parameters overall. My background is based on real world experience with operating, tuning and building real engines of all sizes. My experience includes some theoretical math based design training, but I'm mainly experienced with the hardware and hands on aspects.

Specific to your question here, I can't site a certain example directly, off hand, to validate and support my comments, except to say that my comments are based on my interpretation of the functional details existing with the subject discussion and the relevent technical facts involved.
A detailed explanation supported by reference to established technical principles can be provided for the concepts and conclusions that I am commenting about. Any opposing viewpoints should be evaluated usinjg the same scheme of accountability for accuracy and relevance to the issue discussed.

(fwiw, it took me over an hour to compose this reply, and that is often the case with other posts also. And that is maybe why my writing style is frequently as wordy and formal, not casual. It's hard to relate technical stuff, with a brief spontainious casual style, I don't know how to do that. I took English Comp 101 four times, never did pass that damn course. )

wow. an hour..?

but im just thinking and typing here, but, i would go as far as to say his exhaust is definately causing a restriction. if you think about it, psi is psi, but psi of one volume is not the same as a psi of a much larger volume. so the statement: "The increased back pressure doesn't exist until the turbo has developed about stock boost" doesn't add up. as when the GT71r turbo hits ~4psi, it's probably pushing about the same or more exhaust gas through the turbine and into the stock exhaust. so there in lies the restriction.

just like if you were to remove the exhaust on a completely stock car. the k03 wouldn't spool 1k rpm's sooner, but it would spool sooner and more effeciently up top. and that gap for lower boost threshold only widens as the power and volume levels go up

[A4 Moda]

What's your point? I'm taking all the help I can get. Just because I don't rush to my camera every 2 and a half seconds to take a picture and post up every other 2 and a half seconds about it, doesn't mean I haven't tried it.

Here it is in this order. List of Crap I've already done

1. Checked for boost leak
2. Swapped out my Carbonio V2 for my stock air box.
3. new spark plugs
4. Swapped DV with my friend. YES a FORGE 007, DV. I did swap it. NO change
5. Brand New ATP Manifold V2 or V3, I don't know, but this was 1.5 months ago.

This was all completed within the last 2-3 months.

Yes. the next step is unbolting my exhaust and running it open air.

If you got anything else keep talking.

this thread is kinda aggervating... OP - people are giving you advice, but based on the limited info we have about your car and the rest of your setup, the best and ONLY way that you'll figure this out is to set some time aside and just check over all the little things FIRST.

it's been suggested a few times to try swapping out your DV to see if maybe that's cause, i'd honestly begin with that to save you the trouble of waiting for an exhaust that might end up being too loud for you... only to find out that may not have been the cause (or atleast ALL of the cause) of your late spool. you've got a test pipe, so you're not hitting a wall as soon as exhaust exits the turbo, so you've got SOMETHING right.

do you have optimal flow? no. you dont. do you want a temporary way to find out if that's the problem?? unbolt your exhaust at the test pipe and take it for a spin. it'll be loud as fuck - but you'll find out if that's the problem.

all im saying is quit guessing and go try to fix it.

[A4 Moda]

Thoroughly check your manifold, it may be cracked.

Just got a brand new one 1.5 month ago.
Read above.

Z

[A4 Moda]

Yeah Hence my deduction that V1 doesn't equal V2, therefore, My freaking stock exhaust is bottle necking the stupid turbo. Hence my EGTs, Hence my pulling CFs. SOB !!!!!

I nearly threw my computer out the window when I was sitting at my desk yesterday.

So, you can imagine my disbelief at my myopia of this problem wherein the answer was staring me in the face for the past 6 months.



Oh BTW, I posted this up for everybody else's benefit. Though it may seem most people don't search for the answer, I often do. I woudl like to benefit of having people overpost rather than NOT post. As a consequence, I'm posting this up so that others who may search for some help later down the line may find some. A solution as simple and intuitive as this one can be easily overlooked.

wow. an hour..?

but im just thinking and typing here, but, i would go as far as to say his exhaust is definately causing a restriction. if you think about it, psi is psi, but psi of one volume is not the same as a psi of a much larger volume. so the statement: "The increased back pressure doesn't exist until the turbo has developed about stock boost" doesn't add up. as when the GT71r turbo hits ~4psi, it's probably pushing about the same or more exhaust gas through the turbine and into the stock exhaust. so there in lies the restriction.

just like if you were to remove the exhaust on a completely stock car. the k03 wouldn't spool 1k rpm's sooner, but it would spool sooner and more effeciently up top. and that gap for lower boost threshold only widens as the power and volume levels go up

[DenverNoob]

Backpressure testing should be done here to prove one way or the other. Easier than removing the exhaust. That is way too late for a turbo to be lighting up. I have a feeling multiple components are at work here causing the problem. I am of the opinion, knowing anything else, that if the exhaust were the only problem, you would see a "stepped" boost pattern...a quick run to say 10psi-ish then a far more gradual buildup to full boost as the exhaust continues to choke more and more. Drive pressure would also be good to test if you can (pre_exhaust turbine pressure) and compare that to actual manifold pressure in real-time. That's going to tell you if exhaust related components, inclusing turbo, are at fault. Looking at block 115 will also tell us requested vs actual, another key component here. Just a lot of variables as have been mentioned...valves, n75 function, fueling (are you throwing too much fuel to effectively light the turbo in your boost cycle), etc etc etc. Pulling the exhaust seems to be a bit extreme without the other pieces of info first...of course you could just pull your exhaust and see for grins...but mucho data is needed. Good luck!

[A4 Moda]

You're right about the boost though.
My car jumps very readily up to 5. THen on from 5 is a very very slow and arduous climb to twenty.

Oh and No need for 115. I'm running an MBC. There are no boost connections to the N75. N75 is plugged into the TIp and plugge into the wire harness. That's it.

Boost is completely moderated by the MBC at this point.

Thanks

Z

Backpressure testing should be done here to prove one way or the other. Easier than removing the exhaust. That is way too late for a turbo to be lighting up. I have a feeling multiple components are at work here causing the problem. I am of the opinion, knowing anything else, that if the exhaust were the only problem, you would see a "stepped" boost pattern...a quick run to say 10psi-ish then a far more gradual buildup to full boost as the exhaust continues to choke more and more. Drive pressure would also be good to test if you can (pre_exhaust turbine pressure) and compare that to actual manifold pressure in real-time. That's going to tell you if exhaust related components, inclusing turbo, are at fault. Looking at block 115 will also tell us requested vs actual, another key component here. Just a lot of variables as have been mentioned...valves, n75 function, fueling (are you throwing too much fuel to effectively light the turbo in your boost cycle), etc etc etc. Pulling the exhaust seems to be a bit extreme without the other pieces of info first...of course you could just pull your exhaust and see for grins...but mucho data is needed. Good luck!

[sean1.8t]

You're right about the boost though.
My car jumps very readily up to 5. THen on from 5 is a very very slow and arduous climb to twenty.

Oh and No need for 115. I'm running an MBC. There are no boost connections to the N75. N75 is plugged into the TIp and plugge into the wire harness. That's it.

Boost is completely moderated by the MBC at this point.

Thanks

Z

exactly! like a just posted, boost pressure would only be a restriction from ~4psi and above on a 71r. not 10psi like the k03/k04 would.

i say remove the exhaust. all signs are pointing in that direction anyways. but im only saying this as this would be the thing that i would de since there is only 1 bolt holding my exhaust to the car. for you stock placement BT guys might be a bit more time consuming unless you've done it a few times and know the tricks and right amount of extensions and swivel sockets

[A4 Moda]

Just curious, How did you calculate the 4psi?

exactly! like a just posted, boost pressure would only be a restriction from ~4psi and above on a 71r. not 10psi like the k03/k04 would.

i say remove the exhaust. all signs are pointing in that direction anyways. but im only saying this as this would be the thing that i would de since there is only 1 bolt holding my exhaust to the car. for you stock placement BT guys might be a bit more time consuming unless you've done it a few times and know the tricks and right amount of extensions and swivel sockets

[20vturbo]

when it hits boost do you hear a hissing noise from the exhaust as if the air is compressed in the exhaust..I know on a chipped Jetta and an S4 both with stock exhausts they make that noise....
I am not sure about the exhaust thing....I would remove the turbine housing and look at the blades on the turbine, prob a bitch to do but...
another thing what if you have a bad turbo, not blown but a bad part that went through QC

[A4 Moda]

Yes, I do hear a semi Hissing noise, louder than usual.

And Yes there could be a bad part in the turbo as well. I'm not discounting that possibility.

It ran perfectly fine until I threw the stock exhaust on there.

Thanks for the input!!! This is exactly what the kind of experiences I was looking for.

Just curious, did the Jetta and S4 have the late boosting issues I'm experiencing?

T

when it hits boost do you hear a hissing noise from the exhaust as if the air is compressed in the exhaust..I know on a chipped Jetta and an S4 both with stock exhausts they make that noise....
I am not sure about the exhaust thing....I would remove the turbine housing and look at the blades on the turbine, prob a bitch to do but...
another thing what if you have a bad turbo, not blown but a bad part that went through QC

[sean1.8t]

Just curious, How did you calculate the 4psi?

just a calculation in my head of how much the stock turbo flow vs how much the 71r flows. add that with the stock psi being 10ish.

so i came up with the gestimation of about 4psi. or ~4psi..

nothing MIT worthy i assure you

[diagnosticator]

wow. an hour..?

but im just thinking and typing here, but, i would go as far as to say his exhaust is definately causing a restriction. if you think about it, psi is psi, but psi of one volume is not the same as a psi of a much larger volume. so the statement: "The increased back pressure doesn't exist until the turbo has developed about stock boost" doesn't add up. as when the GT71r turbo hits ~4psi, it's probably pushing about the same or more exhaust gas through the turbine and into the stock exhaust. so there in lies the restriction.

just like if you were to remove the exhaust on a completely stock car. the k03 wouldn't spool 1k rpm's sooner, but it would spool sooner and more effeciently up top. and that gap for lower boost threshold only widens as the power and volume levels go up

I don't agree with your reasoning here. The engine is a fixed displacement air pump, therefore, with the throttle opened before the turbo spools up, the exhaust volume is according to the engine displacement and unboosted volumetric efficiency at that operating condition. The turbo doesn't effect the exhaust volume flowing because it hasn't spooled up yet, therefore the exhaust back pressure is not higher than with the stock turbo at the same pre spooled flow conditions. The exhaust back pressure is a direct function of the exhaust gas mass flow rate in the piping, as the exhaust gas mass flow rate increases, do does the associated gas velocity through the pipe, the velocity of the gas flowing, causes a certain amount of friction and turbulence in the flow stream manifest as back pressure obstructing the gas flow from the turbine Also, a larger turbo, has a larger turbine housing, that results in less kinetic energy of the exhaust gas flow, and lower turbine power available, thus slower / later initial turbo spool up response, etc. Until the exhaust gas mass flow rate exceeds the stock level, the exhaust system has the same back pressure regardless of what turbo is installed. A larger turbo will spool up equally fast on the stock system as it will on a free flowing system, until the the exhaust gas mass flow rate of the larger turbo increases above the flow rate of the stock turbo, then the system will choke the turbo

The above is not the best explanation, I need to leave now, let me know if the situation is still unclear.

[sean1.8t]

i think, that you are thinking about this WAAAAAAY too much.

just think, any back pressure will cause a turbo(of any size) to choke. at all rpms. if you take the entire exhaust off of a stock turbo, that turbo will have a lower boost threshold. it may not be huge but it's there. and that boost threshold will only decrease the larger the turbo size..

but i guess we'll see when he takes off the exhaust

[sean1.8t]

and are you trying to say that VAG engineers designed the stock exhaust system to give no exhaust restriction for a 1.8t k03 car pushing 11psi or less? but anything above that, will give a restriction?

[A4 Moda]

The robot probably wasted too much memory and bus speed to respond to your post. But thanks for your input.


Keep plugging robot!!

[RLB6]

I wanna know who puts on a stock exhaust after upgrading to a 28 series turbo??

You could have quieted your exhaust by replacing the resonators just after the split with Vibrants Ultra Quiet units and by adding a larger diameter one down the downpipe. This would restrict flow a bit but nowhere near the impact of the stock exhaust.

[A4 Moda]

You found him.

Thank you. All options considered.

I hate resonators though. it's either mufflers or straight pipe. Resonators as I mentioned, only kill the rasp. The DRONE gets more pronounced.

The more resonators one puts on, the more of a "purr" you get out of the exhaust, but the passenger cabin becomes unbearable.

I'm going to stick with 3 mufflers.

one for the center and two for the rear. Keep in mind I'm FWD, so I don't have the straight shot quattro/s4 exhaust design. My exhaust piping curves hard left to from the rear to the midsection of the car then snakes to the right. Finally reaching dead center as it gets to the downpipe section.

I wanna know who puts on a stock exhaust after upgrading to a 28 series turbo??

You could have quieted your exhaust by replacing the resonators just after the split with Vibrants Ultra Quiet units and by adding a larger diameter one down the downpipe. This would restrict flow a bit but nowhere near the impact of the stock exhaust.