06_cobalt

So about two weeks ago I installed my GMPP manifold and ZZP downpipe. Immediately after installing I noticed a hissing sound when the car is under boost. Driving normal and not in boost it doesn't hiss. I found the downpipe to catback leaking so I installed a remflex gasket and fixed that leak however the sound is still there. Any ideas? I have checked the torque on everything twice. I'm thinking maybe the flex pipe but it's a new part so it shouldn't be. Also all new gaskets were put in during install and I have a ZZP catback that has been on for a little over a year.

deviance

iTrader: (2)

Catted? I remember reading on here that the zzp high flow cats often make a hissing sound that can be confused for a leak.

Edit: https://www.cobaltss.net/forums/show...43#post7563643

06_cobalt

Yeah 400 cell cat

Staged07SS

iTrader: (25)

You will hear a hiss sound with a high flow cat downpipe. It has alot to do with the harmonics of the exhaust gases flowing through the metal matrix cat. You will get used to it.

06_cobalt

Come to think of it I do hear a little hiss type sound from the cat when I was underneath the car. If that's how it is supposed to be that's fine.

06_cobalt

Thanks man, it is what it is lol.

Staged07SS

iTrader: (25)

Yup... totally normal.