whistling sound under boost

[triplej3]

hey everyone!

last night went for a drive i dont drive the polo all that much these days, was quite cold outside too. at about 20psi car makes a high pitched whistling sound i have no idear what it could be what do you guys think?

iv been running a stage 2 map and have been for quite awhile

[sambb]

I'd bet a beer that its the exhaust mani to turbo gasket. Heat blankets off the charge pipe so you can see what you are doing and then I think a 16mm. You should be able to get away with bending the heat shield out of the way or its a bolt at each side of the head that holds that on. Because of the ribbing on the top of the exhaust mani a spanner rarely works at the ****ty angles you have to work at but if you use a short socket, 3/8th drive and a uni joint with extension you can get onto the bolts. If they are loose, crank them as hard as you can and you may be lucky and the gasket hasn't burnt through. Replacing the gasket isn't hard if it still whistles from the same spot later on. Use a pick to drag the old one out and slide the new one into place. You'll need to remove the steel charge pipe from the back of the motor and the heat shield to do that though. Worth getting a spanner onto any of the exhaust mani to head nuts that you can reach too.

[triplej3]

thanks samb im going to have a look see now ill let you no how i go

[simon k]

And replace the bolts with grade 12.9 cap heads and use nordlocks right Sam

[sambb]

ha ha yep. Thats my recipe!

[triplej3]

alright so i spent my time making sure everything is airtight from tip to gasket, turns out it was the airbox whistling! after deleting secondary air intake system long ago i used some black duck tape to plug the airbox hole that fed into the air pump well that piece of tape had started to come off so i removed the old tape and put new stuff on and bingo! fixed! no more whistle~ just getting my arm around the back of the engine to the manifold was hard enough let alone getting a spanner in there very happy it wasnt the gasket and so glad im a slack **** =p sometimes

thanks guys!

[sambb]

tape!! too easy.

[triplej3]

come to think of it, made a really cool whistle too! google said that it was my turbo failing geez i was worried lol

[simon k]

come to think of it, made a really cool whistle too! google said that it was my turbo failing geez i was worried lol

pffft - never trust Dr Google....

any air that goes through that hole is unfiltered straight into the turbo so do something more permanent than tape. I siliconed a little bit of alloy plate over it from the inside

[triplej3]

your right simon iv ditched the dodgy tape idear and went for a 32mm rubber chair tip from bunnings, really tight fit and i used a hose clamp too. cost $3.60

TIC 32mm Black Round Rubber External Chair Tip - 4 Piece | Bunnings Warehouse

[triplej3]

going to give this a bump, still have an issue with a whistling and boost. in 5th gear on the highway ill peg it to 22psi, will whistle loudly and the car wont hold boost, it will get to 22psi wont hold it and drop back to 14psi and wont boost back up higher then 14-15psi

things iv done so far

fix airbox leak as above, done turbo manifold gasket (gasket looked healthy too) iv checked hoses top and buttom example n75 to wastegate lines, vacuum lines etc they all seem healthy, today im pulling the front bumper off the car to check the intercooler piping (airtek intercooler kit)

[sambb]

To be honest if its hitting 22 psi peak and then drops to 14-15psi afterwards, I'd call that pretty normal. A K03s isn't going to hold anything like its peak boost throughout a pull.
I'd be looking at the boosted side pipework eg turbo compressor to intercooler to throttle body. Look up 'inlet boost leak test' on vortex and you'll find how to do that. That'll definitely whistle under boost. Or check the turbo to exhaust flange too. To check the hot side gaskets you can use the Subaru top engine clean/seafoam method and be ready with a torch to look for escaping white smoke. Doesn't always work but will reveal a bad leak.
You may also remove and check your diverter valve. I wouldn't have thought you'd even hit peak boost with a shredded diaphragm but it could be a worn out base seal on the piston and its just not able to hold max boost without spilling over. Unlikely but possible.
Really audible whistling under boost though.... my odds are on an air leak to atmosphere somewhere.

[triplej3]

fixed it

tightened and adjusted all clamps and hoses on the intercooler, tightened up the sensor thats on the bend off the throttle body hose was able to use two nuts to get it really tight. all seemed quite good as it was. throttle body hose was slipping from the bottum but not by much, brought a more heavy duty clamp for it. didnt find any split hoses or damage so not sure just happy it doesnt sound like a referee ahh =p

samb thank you