KevinEF7

Just trying to determine the cause of a boost flutter that came about when i raised the boost pressure in my car from 15-16psi to about 21-23 psi.

My setup is very simple with a knockoff 38mm wastegate, I believe a 10psi spring, and a good MBC with its source coming straight from the compressor housing

Up until today when running 16psi, it would hold steady boost the entire rpm band, very little if any fluctuation on the gauge.

When I raised the boost a quarter turn on the mbc and did a pull, the boost flutters very rapdily on the gauge between 20-24psi and you can hear a fluttering (not constant, more of a pulsing sound) coming from what I presume is the dumptube exhaust note

Is this a sign of a wastegate spring that needs to be upgraded? bov possibly (running crushed dsm 1g)? A sign of anything else?

Could go into alot more detail but didnt know if this was common failure that occured when raising the boost pressure

Black R

eBay wastegate? There's your problem.
What mbc?

TheShodan

iTrader: (14)

Yeah. Better gate, plus increasing the spring rate a bit with a stronger spring.

KevinEF7

Yes its an ebay wastegate, its the mini 38mm version that alot of users recomended on DSO, but I am unsure if any users went to this boost level

I was just out playing around with it, seems when set to about 18psi it will hold steady, but another quarter turn on the MBC and it starts flutterring, about 20psi Id presume. Is this fluttering negative at all or is the boost just not constant? The afr's stay well within range

It is an NXS motorsport MBC

Black R

Tial has published info on their site explaining why eBay gates are not a good idea.
One of the reasons is that the subpar materials can't handle the stresses of heat cycling and have all kinds of strange failures.
The rates of the springs also aren't consistent.

motoxxxman

the dsm BOV is known to flutter open and closed at higher boost pressures. that's why they crush them, which usually only holds it to another 2 or 3psi higher than stock.

chances are the BOV is to blame. get a normal bov.

ebay wg's don't flutter, they simply work or they don't, and they fail easily.
its also possible the mbc is almost maxed out

KevinEF7

My bov is crush modded. But im not ruling it out .

Holds 16psi all the way to redline, and feels strong, but when the boost flutters when I up the psi the car feels slower.

Doesnt help that I have no traction

Freemananana

iTrader: (3)

Don't want to disagree, but most of the fluttering I've heard has been from BOVs.

Obviously, better wastegate would be a good choice. But it's not always an option.

KevinEF7

Definetely sounds like a fluttering/pulsing coming from the engine bay. My dumptube dumps just under the engine

I just wrinkle painted the dam BOV to, hate to damage all that to crush it a little more

Muckman

iTrader: (2)

Are you positive combustion is not breaking up? Hows the AFR when this happens?

wantboost

iTrader: (2)

^this have you logged a pull/read plugs?

you could be out of pump/injector or ignition

also, normally double the spring pressure is about all a wg will do, regardless of size/brand. most of the times the knockoff brands have issues with the bushing/seal between the valve shaft and wastegate body going bad, allowing exhaust gasses to enter the top half and cook the diaphragm.

also, due to the turbulence in the compressor housing/varying pulses/ airflow sometimes higher boost pressures can be problematic. try moving the signal line to the intake manifold

KevinEF7

Not positive, plugs are fresh and gapped to .028 , BRK7E's. AFR is steady at 11.7-11.9.

I dont have logging ability with Turboedit, but I did a 4th gear pull and as soon as it flutterred I killed the ignition and pulled a plug, looked perfect.

Pump is a near brand new walbro 255 @ 45psi base, 10gauge hardwired, presicion 680cc injectors. I think Im ok for fuel, im guessing im around 300-325whp

Muckman

iTrader: (2)

Ok then it's not breaking up if AFR is steady

wantboost

iTrader: (2)

gotta be the wastegate then

TheShodan

iTrader: (14)

yes. and when controlling boost sometimes they do that. I've give some other examples.

0:28 Seconds of this video...Wastegate will flutter when in not fully opening and controller will actuate the valve.


Of course this was one of my favorite videos of all time.

motoxxxman

I'm still leaning towards that DSM BOV. three's a reason people crush them: because they creep open and flutter when raising boost above stock. and crushing them does not increase spring pressure or spring rating, it merely increases seat pressure, which causes it to not creep until a slightly higher boost level but it actually makes it MORE prone to fluttering when it reaches the point of creep.

I'd be willing to bet if you replace the bov with something name brand, the problem will be gone for good.

you said you're using a manual boost controller. issues with boost flutter when raising the boost typically only happens when using an electronic boost controller, it almost never happens with a manual controller, even with the crappiest of crappy wg's.

wantboost

iTrader: (2)

I've seen crushed DSM valves hold high 20s if they are crushed right

Tony the Tiger

There are couple of easy steps to detemine the flutter

If the car is open WG dump, does the flutter also make your wastegate dump open (and create dump sound). If yes, then it is probably the wastegate spring too soft.

Does the boost gauge show erratic boost readings during the flutter? If not, then it is a compressor surge problem. Considering I see a single cam engine, running the turbo beyond surge line is pretty plausible at that boost level.

To isolate the wastegate, you can set the fuel/timing maps to be conservative and boost cut to safeguard the engine, and then hook the vacuum line to the top port of the wastegate (warning: it will be maximum boost pressure, so don't do a full pull). You will probably hit boost cut, but if flutter is still there, then it has nothing to do with the wastegate.

wantboost

iTrader: (2)

I never considered surge, good call... Single cam, decently sized turbo at high boost pressure = surge city

If it's only at lower rpms (as soon as boost gets above 16psi or where ever the flutter starts) and clears up as you rev it out it could very be surge, trying to stuff more air into the motor than it can ingest means air reverting back through the system