my old g6 did that, mine was belt tensioner

 

leave it up to a turbo newb!!! HAHA

i tried making a recording with our new camera... it picks up horrible noises ive never even heard haha.. but mostly my chevy bowtie ket chain...

but anywho i took it down the road to get footage..

its got to just be the "stomping the throttle" .. it does it only at the 20+ mark on the boost gauge as it shifts to 2nd or 3rd?...

now if it is the blow off... why even when it was factory and stg1 kit only and now with a forged bpv (yellow spring) does my boost only go to 20-23?

shouldnt it go a lil higher with the stiffer spring and new low mileage bpv?

but to end all concerns i think its just the sound of the turbo blow off i am not use to being behind the wheel of A turbo :) .. i have always been an onlooker of turbo vehicles never owned one and only been in one other turbo before (other then diesels, i was in a eagle talon a couple times)

 

I wish mine boosted to 23 psi. I can barely hit 20. PSI readings will vary depending on temp,elevation, barometric pressure, blah blah blah. U get the idea. The more dense air is the less PSI u will see.
The way you are describing it "mashing on throttle and you hear a belt slipping sound ONLY when tranny shifts" sound like its the clutches in ur tranny. But I don't think it's anything to worry bout. My auto did this with GMTU under 10k miles.

 

X2. Don't think I'll ever hit 20. 19 is the most I've seen. BUT, I am at sea level so elevation,air quality, barometric pressure, blah blah blah. Remember,it's not how much PSI you make but how much power.
I have seen mine hit about 310 tq. on my RPD, so I know I'm producing the power.

 

newb?

 

It's all in the GMTU tune I'm sure. My 09 auto would hit 21-24 psi no prob. But now with my 2010 5sp it's only 20 peak(both with GMTU) I have checked the RPD and I hit 310-320 torque briefly so it's on par.
I should add the auto in my sig so I dont confuse anyone...

 

Mine did it too under hard acceleration. Its an auto thing. Went away when I installed a new gatorback belt.

 

Yours did it as tranny shifted?

 

yup

 

^^^good find. Results better than speculation. Stupid POS factory belts.