On boost flutter after turbo discharge pipe install. Boost leak or compressor surge?

I installed a turbo discharge pipe tonight and noticed a "flutter" afterwards that I've never heard before. I've been able to nail it down to around 3800-4000 RPM in either 3rd or 4th gear when @ WOT.

https://youtu.be/YchbBvty-iI

Current related modifications are an Evoms intake, DV+, and this new pipe. This is at stock power levels still.

Here's the graphed log from a 3-4-5 gear change on the highway. What do you guys think of that second boost request hump on each gear change?



What I'm trying to determine is if I have either a simple boost leak from not tightening a hose clamp enough (causing air to leak when it builds up high enough and then the seal re-seals once enough has leaked out) or if I'm actually getting some compressor surge. The latter is known to occur once tuned but obviously I am not yet.

And of course, the big question is, "is this dangerous?". Thoughts?

Interactive Log Chart: https://docs.google.com/spreadsheet...yHI/pubchart?oid=708703803&format=interactive

lateapxr said:

I installed a turbo discharge pipe tonight and noticed a "flutter" afterwards that I've never heard before. I've been able to nail it down to around 3800-4000 RPM in either 3rd or 4th gear when @ WOT.

https://youtu.be/YchbBvty-iI

Current related modifications are an Evoms intake, DV+, and this new pipe. This is at stock power levels still.

Here's the graphed log from a 3-4-5 gear change on the highway. What do you guys think of that second boost request hump on each gear change?

What I'm trying to determine is if I have either a simple boost leak from not tightening a hose clamp enough (causing air to leak when it builds up high enough and then the seal re-seals once enough has leaked out) or if I'm actually getting some compressor surge. The latter is known to occur once tuned but obviously I am not yet.

And of course, the big question is, "is this dangerous?". Thoughts?

Interactive Log Chart: https://docs.google.com/spreadsheet...yHI/pubchart?oid=708703803&format=interactive

Click to expand...

First thing's first. Logs look optimal. If you want a double check, log the N75, requested and actual boost from a few 4th gear pulls.

Second - you say you're at stock power levels? Sounds like you've got a downpipe and you're boosting to 18psi peaks. You're definitely tuned.

Lastly, I don't see the flutter as being much of an issue. Yes, you're maxing out the flow of the turbo and are getting a little bit of surge oscillation, but no stalling. All things considered I wouldn't worry about it.

XGC75 said:

First thing's first. Logs look optimal. If you want a double check, log the N75, requested and actual boost from a few 4th gear pulls.

Second - you say you're at stock power levels? Sounds like you've got a downpipe and you're boosting to 18psi peaks. You're definitely tuned.

Lastly, I don't see the flutter as being much of an issue. Yes, you're maxing out the flow of the turbo and are getting a little bit of surge oscillation, but no stalling. All things considered I wouldn't worry about it.

Click to expand...

I realized as much after I did those logs and saw the graphed output that it'd definitely be more enlightening to see the N75 duty cycle on that graph. I may end up redoing them now.

I'm still stock though! I have a downpipe waiting to go in but because I haven't been able to schedule time to do the install, it's still sitting on my living room floor.

I haven't gotten tuned yet for warranty reasons (it expires this December) mostly, though I'm insanely curious to see what can be gained by changing out hardware first before software. I'm installing all the supporting UM S2 pieces before getting the tune in the meantime.

I get the exact same thing after installing my Neuspeed discharge pipe as well. I agree with XGC7, my guess is it's simply just a lot of air flow. My hunch is it's caused by the restrictive stock downpipe as with a bigger discharge pipe, it's obviously pushed a bit more...

The other possibility I thought it was is my DV leaking only at max boost. I'll most likely throw in an upgraded DV someday, but it was just a thought. I'm not sure if that'd cause the flutter though.

I also want to pull some logs on this, but just haven't had the time yet. Although I'm actually boosting to 23.5psi at max (reading came from a boost tap)...

tjasko said:

I get the exact same thing after installing my Neuspeed discharge pipe as well. I agree with XGC7, my guess is it's simply just a lot of air flow. My hunch is it's caused by the restrictive stock downpipe as with a bigger discharge pipe, it's obviously pushed a bit more...

The other possibility I thought it was is my DV leaking only at max boost. I'll most likely throw in an upgraded DV someday, but it was just a thought. I'm not sure if that'd cause the flutter though.

I also want to pull some logs on this, but just haven't had the time yet. Although I'm actually boosting to 23.5psi at max (reading came from a boost tap)...

Click to expand...

It looks like I'll be installing my downpipe this Saturday finally; I'll report back whether it made any difference in the flutter or not.

I don't think a leaking DV would exhibit this same behavior; compressor surge / flutter is caused by too much pressure build up and a leaking DV would actually prevent it. Before I installed my DV+ bits, it seemed like my DV was leaking a bit and the symptoms of that was a boost gauge that showed my pressures spiking and holding but only momentarily before they'd slowly decrease. After the DV+ it spikes and HOLDS steady all the way to redline. Unlike the K03 in my old MKV GTI, the K04 never seems to run out of breath :happyanim:

lateapxr said:

It looks like I'll be installing my downpipe this Saturday finally; I'll report back whether it made any difference in the flutter or not.

Click to expand...

Sweet! Man, if it fixes it, I may have to suck it up and throw on a downpipe.... keeping my R legal was something I was trying to do. haha

lateapxr said:

I don't think a leaking DV would exhibit this same behavior; compressor surge / flutter is caused by too much pressure build up and a leaking DV would actually prevent it. Before I installed my DV+ bits, it seemed like my DV was leaking a bit and the symptoms of that was a boost gauge that showed my pressures spiking and holding but only momentarily before they'd slowly decrease. After the DV+ it spikes and HOLDS steady all the way to redline. Unlike the K03 in my old MKV GTI, the K04 never seems to run out of breath :happyanim:

Click to expand...

Yeah, because neither of us have an issue with boost; even my car with the stock DV can hold the boost. Not forever as I'm sure it's leaking a bit, but it's definitely not massive boost loss.

When the boost builds up, it'd make sense why it sounds like the fluttering is coming from my air intake.

Well, installed the new downpipe today and it did nothing to reduce the flutter/compressor surge. If anything, it made it a bit worse actually. Now it spikes up to 19-20psi before the wastegate kicks in and brings it back to stock hold levels.

My guess is that all of the tuners simply tune this behavior out and that this will go away once I eventually go UM S2. It really only happens when full WOT and only during a well defined portion of the RPM band. Until then, I'm just not going to go full WOT and will just change the behavior of my right foot.

I'll still run some new longs and post them back here once I get a chance though.