heinous noise from -3psi to +3psi
 

I noticed this last night, for a while I thought it was the DP rubbing something. In that 6-psi range, I get a horrible noise, rhythmic, and I don't really know how else to explain it. Its not high-pitched...sounds like the DP is rubbing, but its not. I'm fairly certain its coming from the turbo. Its a rhythmic resonance...the only thing I can equate it to was when we'd get 2 VR6s next to each other, and the howl of the motors would resonate a dissonace.

I basically can't use cruise control because of it.

Any thoughts? Hopefully not compressor surge. Any chance I could be on the short-side of the surge line at 3psi?

oh man, after a few in-car vids from youtube, compressor surge may be a possibility...but my gauge isn't going crazy, it holds steady.

Maybe its time to get an anti-surge compressor housing. lol

Is it the turbo or the actuator rubbing on the frame lip? That is another source of vibration/noise.
Stephanie

negative, lots of clearance. I'll try to get audio in the next few days.

Slight leak from a vaccuum hose, or a torn diaphram in your wastegate or bov perhaps? You have access to an air compressor to do a boost leak test?

C

I guess I need to make one of those leak-test kits. It would be cool to find a leak...faster spool and less heat.

It may also be your boost gauge buzzing. Disconnect it to check.

I'm kinda iffy on both my suggestions though, since it's happening in vac and boost. Just throwing ideas out there.

C

i don't think its the boost gauge...this is loud as hell, cars next to me will look over. It also produces "the brown note" so I'd like to fix it so I stop shitting myself.

lol.

I get compressor surge like a mother fucker. In Vac or below 2 psi most of the time...I can't figure that one out.

any chance it could be something funky with my re-routed bosch blow off valve?

we need audio

I found my noise. IC pipe rub. Oddly enough it's way louder inside the car than listening to the engine bay- and sounds totally different. I use the left hand to run the revs up at the TB until it introduced a new sound and then I started pulling on anything that was flexible. Grabbed the hotside IC pipe and when I pushed on it, I felt the vibration. When I pulled it went away along with the noise.

LOL South Park FTW.

I would really like to know if you are getting surge too. Believe it or not I am STILL not sure if I can get the GT2871 with the anti-surge housing. So if you are having boost build compressor surge issues (not BOV related) with the potato, and I am going bigger on the compressor, that concerns me.

I am also getting a smaller .64 AR on the turbine. Based on my limited knowledge I would think that would make things worse since that would tend to spool the compressor sooner.

You know the more I think about it, the more I am not so sure this is surge?

At 3 psi the pressure ratio of ~1.2 is such that you are very low on the map. The surge line at 1.2 PR for the disco potato is about 5 lb/min airflow, which equates to what, about 40-50 HP? So unless you are making less than 50 HP where this is happening then maybe it is not surge?

Plus you said your gauge is not vibrating. I suppose it is possible that something in your gauge system is damping out the pulses, and thus it could be surging. But it seems like something would still be visible?

BTW according to ATP Turbo tech support the GT2871 is available with the anti-surge housing. Phew.

boost gauge stays steady.

I had an IC piping rub....it was a GOD awful rattle on decel for the most part.

On my S2 kit, the DP would not touch if the car was off or at idle. From the same, -3 psi to +4 or 5 psi, the DP would hit the sub frame and create a similar sound to what you are describing.
I just took a leap on diagnosing it and would tighten the DP together. The noise would be less and then eventually get worse and louder. So then I had to put a little dent in the dp where there were scratches (minute, not enough to really say "here is the problem")... put it all back together and no more noise.

Its funny. Wouldn't touch at all except during a certain amount of vaccum/boost.

to reiterate what others have said, check the clearances of things in the engine bay while revving the motor, holding it at different rpms, etc because things move a surprising amount. Would be even better if you had some of those small portable vid cameras with suction cups that you could mount in the engine bay, drive around, and see if anything is hitting when the sound happens..

Does this happen only when driving, or even when sitting still and revving?
If the latter, have someone rev the car in that range while on the lift if you have access to one and just pry around the engine bay and the entire exhaust see if you can narrow it down this way. Sound clip will help get a better idea of what it may be. It could really be anything atm.
Ex: I once had a noise that I swore was coming from the enginebay, but it turned out to be my rear most muffler hanger broke at the weld and rattled. Weired shit!

I've used a pipe from an old shop vac more than once to find odd noises - like a humming idler pulley.
I hear these work too. - $5
http://www.harborfreight.com/cpi/pho...1999/41966.gif

Big money version @ $37
http://www.harborfreight.com/cpi/pho...5699/95653.gif