N249 delete: Why you should not do it.

[phila_dot]

One thing ive seen pop up a lot if running divertervalves backwords for quicker response. Im curious if this is true or not...

Looks like you're in a position to find out.

Flip your DV's, run those logs again and see what difference, if any, it makes.

[julex]

Look at any compressor map, look at close to no flow X-axis position, follow up to the compression ratio you get your spike at and now tell me if your turbos are surging or not... There is nothing to argue. Instead of pushing air out (as would happen with DVs open), the compressor blades are chopping stalled air and the difference in speed is supersonic.

Tial 770 (my set up) compressor wheel is 68mm. Linear speed at blade edge at 150k rpms (that's probably the speed of wheel it is spinning at WOT near red line) is 534.071m/s. Speed of sound is 340m/s. Surge when air is not moving is guaranteed. On smaller turbos the difference will be smaller, perhaps not audible even as they might be slowing much faster as well given much smaller inertia due to smaller compressor wheel (and perhaps smaller hot side as well). I also have very open intake with very large Y-pipe and straight cone filter which makes things audbile.

You should hear my my turbos surge/flutter/resonate at low boost acceleration one of these days. "choke, choke, choke", literally, if I throttle them just right. That's surge on turbos when turbos are pushing but throttle is closing to keep load at requested level. Very visible in logs when TBB sensor shows much higher pressure than me manifold zeitronix does and load level is moderated via throttle.

[Meow]

Look at any compressor map, look at close to no flow X-axis position, follow up to the compression ratio you get your spike at and now tell me if your turbos are surging or not... There is nothing to argue. Instead of pushing air out (as would happen with DVs open), the compressor blades are chopping stalled air and the difference in speed is supersonic.

Tial 770 (my set up) compressor wheel is 68mm. Linear speed at blade edge at 150k rpms (that's probably the speed of wheel it is spinning at WOT near red line) is 534.071m/s. Speed of sound is 340m/s. Surge when air is not moving is guaranteed. On smaller turbos the difference will be smaller, perhaps not audible even as they might be slowing much faster as well given much smaller inertia due to smaller compressor wheel (and perhaps smaller hot side as well). (You also forgot to add that your 770s are ball bearing with less friction and wont slow down as fast as a typical journal bearing turbo) I also have very open intake with very large Y-pipe and straight cone filter which makes things audible.

You should hear my my turbos surge/flutter/resonate at low boost acceleration one of these days. "choke, choke, choke", literally, if I throttle them just right. That's surge on turbos when turbos are pushing but throttle is closing to keep load at requested level. Very visible in logs when TBB sensor shows much higher pressure than me manifold zeitronix does and load level is moderated via throttle.

However, you do not jump straight to the no flow area. You reduce flow out of the turbo, but it doesn't jump straight to zero cfm or lb/min or whatever you are using for flow. There is still flow.

That could be why you hear surge and I do not. My maf still reads air being drawn through during the spike. I know its not perfectly accurate because you have to think of the response time of the maf to changes and the signal rate of the maf sensor and the difference between the rate of collection from the maf and the map sensors. Yet I think we are on to something here.

I added maf signal to the screen shot of my log I showed earlier. Here you can see my flow does not instantly go to zero and I stay below the surge line. While with your larger turbo with more rotational momentum and smoother bearings spike higher pressure levels, you likely move off the edge and into the surge region. I do not think this happens on a k04 car as the turbo slows down faster, spike less and maintain below the spike range.

[Meow]

Looks like you're in a position to find out.

Flip your DV's, run those logs again and see what difference, if any, it makes.

I missed this response somehow. I will try to do that this weekend and get some logs.

[julex]

However, you do not jump straight to the no flow area. You reduce flow out of the turbo, but it doesn't jump straight to zero cfm or lb/min or whatever you are using for flow. There is still flow.

That could be why you hear surge and I do not. My maf still reads air being drawn through during the spike. I know its not perfectly accurate because you have to think of the response time of the maf to changes and the signal rate of the maf sensor and the difference between the rate of collection from the maf and the map sensors. Yet I think we are on to something here.

I added maf signal to the screen shot of my log I showed earlier. Here you can see my flow does not instantly go to zero and I stay below the surge line. While with your larger turbo with more rotational momentum and smoother bearings spike higher pressure levels, you likely move off the edge and into the surge region. I do not think this happens on a k04 car as the turbo slows down faster, spike less and maintain below the spike range.

Yeah, well, one major counter I have here is that maf sensor voltage is non-linear. So much so that at 1.8V a typical 85mm hitachi maf will flow something to the tune of 115 l/h while at 4.2V it is 925 l/h (I pulled these from nefmoto stage 3 tune I have bin for).

So here you're dropping from 925 l/h to 115 l/h flow within 0.1s...that's rather drastic reduction in flow and for all intended purposes represents practically completely choked channel without a way for air to anywhere but to stall and start going backwards through the turbos if the DVs are super lazy and slow.

[Meow]

Yeah, well, one major counter I have here is that maf sensor voltage is non-linear. So much so that at 1.8V a typical 85mm hitachi maf will flow something to the tune of 115 l/h while at 4.2V it is 925 l/h (I pulled these from nefmoto stage 3 tune I have bin for).

So here you're dropping from 925 l/h to 115 l/h flow within 0.1s...that's rather drastic reduction in flow and for all intended purposes represents practically completely choked channel without a way for air to anywhere but to stall and start going backwards through the turbos if the DVs are super lazy and slow.

Good point. I am slightly larger diameter than that so the change is even more drastic.


I wish I could say I was hearing surge on throttle lift off and just agree, but I hear nothing of the sort... I still don't think that k04s surge in this situation.

I do agree however that these diverter valves (710n) are lazy and slow.

[julex]

Good point. I am slightly larger diameter than that so the change is even more drastic.


I wish I could say I was hearing surge on throttle lift off and just agree, but I hear nothing of the sort... I still don't think that k04s surge in this situation.

I do agree however that these diverter valves (710n) are lazy and slow.

Here is a graph for you with N249 functioning (so there is no boost spike). Important to note here is that I show you two MAP sensors, factory location one (4bar range though) and zeitronix in intake manifold. Zeitronix shows in PSIs, so negative PSI means a measure of vacuum. As s refresher, -14.5 PSI would be absolute vacuum which is also 29.97 inhg. So -10PSI is roughly ~20inhg - typical vacuum between idle and after run.

Also, pay attention how long it takes the manifold pressure to fall below -7psi which is when DVs activate without N249 assist.

[Meow]

Can you zoom in to between 23.5 and 24.5 on that graph? Or post a picture with the values in excel.

[julex]

Can you zoom in to between 23.5 and 24.5 on that graph? Or post a picture with the values in excel.

PM me your email, I will send you the log.

[Meow]

Looks like you're in a position to find out.

Flip your DV's, run those logs again and see what difference, if any, it makes.

So I tested this theory today. I flipped them and did a bunch of logs, this is about the average of what I saw. Somewhere between a 6-10psi spike with them reveres. From this alone I would say they are just as bad, if not worse when flipped. No real difference in sound.

So running them in the normal position is your best bet.

[boostk420]

So bringing an old thread back to life. I want to do the bypass for n249. I feel like mine is doing the ecu controlled (limp mode) replaced n75 so its not that and also have an MBC inline. However still get low boost code. I will hit 13.5 psi and hold with the MBC under WOT but MBC is wide open, so no boost leaks. Here is the thing. How much longer does it take for the DV to open with just manifold vacuum? Vs. The DV opening by n249? Also

How can the n249 produce the vacuum required to open DV before the manifold physically sees the vacuum and reaches -psi./hg?








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[vavJETTAw36]

So bringing an old thread back to life. I want to do the bypass for n249. I feel like mine is doing the ecu controlled (limp mode) replaced n75 so its not that and also have an MBC inline. However still get low boost code. I will hit 13.5 psi and hold with the MBC under WOT but MBC is wide open, so no boost leaks. Here is the thing. How much longer does it take for the DV to open with just manifold vacuum? Vs. The DV opening by n249? Also

How can the n249 produce the vacuum required to open DV before the manifold physically sees the vacuum and reaches -psi./hg?








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What turbos do you run firstly?


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[boostk420]

What turbos do you run firstly?


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Stock ko3. I assume being a 2004 A4 1.8t AMB, or AWB its one of those.

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[vavJETTAw36]

Stock ko3. I assume being a 2004 A4 1.8t AMB, or AWB its one of those.

Sent from my XT830C using Audizine mobile app

How much boost is it tuned for? Are you not making enough boost or are you overboosting?

It's not a good idea to bypass any ecu controlled failsafe. You should fix the root cause.


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[christianb5s4]

I don't know why you wouldn't just replace the N249 if it's truly faulty? They aren't dirt cheap but no unreasonable, you can also get a used one including related hoses from parts stores like audis4parts.com for cheaper if you so choose.

https://www.ecstuning.com/b-genuine-...49/078906283a/

[MetalMan]

So just to be clear, you own a 2004 1.8T? The N249 is a different part number than what Christian posted if you own a B6 A4.

[nnik]

thanks for the clarification...

so...per somedude's response, the claim OP made is not so valid...??? Julex...not to bash on you but i'm just reading in between the lines here...
i want to make sure the claim is substantial enough for me to justify restoring to original / intended config...

If you really think about it and do some research it a well- worded load of crap..... You know.... The kind lawyers use.

[armageddon-]

I can tell you that I have n249 installed and I get the boost spike. I even replace it for a brand new one, makes no difference...

[CELison]

I don’t have the n249 and I don’t get any boost spikes.

[Mocke]

I can tell you that I have n249 installed and I get the boost spike. I even replace it for a brand new one, makes no difference...

Tune it out.

[armageddon-]

I do not like remove things just because... it has its function, but in my case at least, it doesn't reduce/remove the spike. I replaced it thinking that it should had not working good, but made no diference with the new one, spike still present.


For what is worth, I never run with it removed, so I do not know if the spike would be worse or not.

[Mocke]

I do not like remove things just because... it has its function, but in my case at least, it doesn't reduce/remove the spike. I replaced it thinking that it should had not working good, but made no diference with the new one, spike still present.


For what is worth, I never run with it removed, so I do not know if the spike would be worse or not.

Ohh. Misunderstanding.
249 is never to be removed.
I thought you should tune out the spike if you got it. Its not cosing TC after shift??
If not - don’t worry about it - unless its a big one.

[armageddon-]

Ok, this is not mine, but a friends rs4 that I help with tune, mine is similar, not so big but is there...

I have other friend with rs4 that has same spike.

Mine and both rs4 have n249 installed.

One rs4 had rs6 hybrids, other gt28's and my S4 has k04

[Timtheguru]

Ok, this is not mine, but a friends rs4 that I help with tune, mine is similar, not so big but is there...

I have other friend with rs4 that has same spike.

Mine and both rs4 have n249 installed.

One rs4 had rs6 hybrids, other gt28's and my S4 has k04

What diverter valves are you running on both cars? Since the N249 actuates the diverter valves, this is also important to consider.

[armageddon-]

Mine and one of the rs4 uses 710N, the other rs4 some no name like forge 007

[rnagy86]

Guys, the problem is not with the n249. The problem is the tiny holes on the pressure pipes that are connected to the DVs. I cut mine off from the rs4 pressure pipes and got them re-welded with proper 25mm ports to match the DVs and since then I don’t have spikes at liftoff.

[armageddon-]

Probably, I noticed that the hose me a very tight bend...
mine is stock, one rs4 is also stock, but the one from the graf has The-Tuner bi-pipes.

[rnagy86]

Probably, I noticed that the hose me a very tight bend...
mine is stock, one rs4 is also stock, but the one from the graf has The-Tuner bi-pipes.

The tuner bipipe is useless especially that the DV port is also as small as OEM.