Engine Screams Under Boost (audibly not metaphorically)

[Ski Bum]

So I've ran multiple boost leak tests revealing leaking TB shaft seals, lower injector seals and a few misc. vacuum lines that I in turn replaced/fixed. Now I can pump 25psi into the intake with leaks only coming from th oil cap and dipstick. If I hold the dipstick and oil cap down the 25psi will hold. So I should be good to go right? Nope, something is still leaking... I think.

Under boost something screams/whistles like I've never heard before. It only occurs under heavy boost, 10+ psi. I cannot get the sound to duplicate itslef with the boost leak test and cannot pinpoint where in the egnien bay the sound is coming from while driving. I thought it may be the oil cap but there isnt any oil around the cap or on the valve cover after it occurs.

The last time the turbo (14B) was out fo the car I did some pretty extensive P&P to the exhauist housing and O2 housing. This has produced some pretty good boost creep at times. Upon inspection I did notice a little shaft play. I could actually move the shaft forwards and back about 1/8". The movement up/down/left/right was just a little less then that. So I now know that the turbo doesnt have much life left to it. Anyways, would excessive shaft play cause a leak or a sound like that? What symptoms should I look for asscociated with excessive shaft play?

I will get a recording of the sound if you guys think it will help to diagnose.

 

[UNDER_PRESSURE]

I've heard this before and I'm pretty sure it's coming from the turbo my friends car did the same thing at 22 psi. He was scared as fawk cause he had never heard that noise before but the look on his face was priceless after he was at full boost. .

 

[Shane2GSX]

Same thing happened on my 97 GST with the T25. It would almost screech. The blades in the turbo were hitting the housing. I would check yours for shaft play.

 

[UNDER_PRESSURE]

The turbo was fine it was just the high boost levels I believe, He's gotten a Big 16G since then.

 

[Ski Bum]

I havent ran more than 15psi with a MBC and it makes the noise then. I dont think its too much boost, perhaps the shaft play though.

 

[UNDER_PRESSURE]

Could be but have you checked turbo for shaft play.

 

[tranceman]

I had the same type of sound in the past and it was my coupler on the turbo. I didnt have the clamp as tight as it should have been. I am sure you have checked that during your boost leak test but its another idea.

 

[majik2k5]

Well, there are two scenarios here.

With my first turbo, when it was ported the turbo spooled faster and it was actually the turbo I could hear spooling that sounded like a whining sound. It was loud, but not defening and it didn't overpower the engine noise.

However, with my second turbo on my car, it began a loud screeching noise that was clearly audible over the engine, and actually at times more overpowering than the engine.
I pulled the turbo off and noticed that the exhaust turbine blades were hitting the turbine housing every now and then.

So I ported about an 1/8" off the edge of the inside of the turbine housing, and had the inlet and outlet ported as well while I was at it. I didn't lose any performance from doing so, but that could be because of the porting of the inlet and outlet.