I just installed a turbo back today and everything was going fine, now for some reason when I go over 6000 rpms and the boost is 19-21psi I hear a loud squeal sound and I lost about 5-8psi of boost. I know it not the turbo sound because I know what that sounds like, but it does not do this every time sometimes it holds the boost fine to redline. Any help would be great because I don't think I am going to have much luck with the dealer.

 

well that's normal on a stock evo... don't know why you are just noticing it now. a turbo back is pretty hard to mess up installing, maybe you didn't tighten everything correctly or you are missing some gaskets...

 

A loss of 8 PSI is normal? You need to take your Evo into the dealer for some warranty work if you're seeing an 8 PSI drop as being normal. As for the original question: Dunno.

 

running a test pipe?

 

No test pipe and it was holding the boost fine before the turbo back install. I also notice a sound like squeaky car brakes when it looses boost and even my wife said "What's that noise" so I know I can hear it and when I hear it I lose boost, and I can hear it from the motor area just hard as hell to trouble shoot the problem. I did check everything and I am still getting like a 5-8psi drop and it used to hold 19-20psi to redline now it's like 15 or even 1 time it was 12. Also sometime it holds boost to redline as well.

 

Could it be the blow off valve?

 

It could be the BOV but I doubt it.
Is it the stock BOV? And are you running the stock boost control and levels?

Most likely you have a loose hose that is leaking the pressure off.
It seems to be pretty common occurance. Check all of you IC hose clamps for tightness. In particular a lot of people have found the hose from the upper I/C pipe to the BOV to be loose.

 

Ya, I have the stock bov on the car and am running about 19-22psi. It does sound like it's leaking pressure because it hold 22-24 psi spikes it's just at high RPM it start to lose pressure and a leak does sound right because of the raised pressure.