Funny question huh? I have been thinking exhaust leak on this one but here's what I have been through.

When I first got the car I dont remember any hissing but that was 6 years ago and I wasn't listening.

I put shorty headers on the car before I was Corvetteforum enlightend and knew I could get LT's. After a while I noticed the hissing. Went all through the exhaust system many many times with new gaskets and retightening, etc.

Had a clutch and Flywheel change. Sold the shorties, Put Manifolds back on. Still hissing. Unbolt everything. Retighten everything. Still hissing.

Think my manifold might be leaking. Take it off and RTV it. Still hissing. Remove the entire EGR/AIR system. Put blocking plates on rear of the intake manifold. Still hissing.

Get new hooker LT's. Use copper gaskets and get complete new exhaust all the way from the collectors to the tips new 1 piece. Still Hissing. Decide the Coppers aren't sealing so I get Felpro 1406 and use a bunch of RTV. Also use RTV on the collectors with new gaskets. Still hissing.

Now I'm not hearing a puff, just a hiss and it works itself along with the powerband. It sounds like air escaping but it might be the drivetrain.

Could it possibly be the drivetrain? Am I not getting the Header Bolts tight enough? I am scared of this because of alumnum heads... What can I do to check? I wish I could dye exhaust gas and see it come outta a hole. :lol: Does anyone else LT-1 sorta make this noise? :(



For all you Jokers.... :jester

 

Are you sure its not the airbox? I noticed after I went to the BBK 52mm I had a hissing sound coming from the air box

 

Hmm Doubt it. I put the stock Air box back on it an it sounded the same. Could be something with the TB itself maybe....

 

how about a clogged catalytic convertor? mine did that, then i hollowed it out and no more hiss! :seeya

 

Nope I aint got no Cats. :seeya

 

Is this under idle or full throttle? if its full throttle check to see if the air filter duct is not collapsing under load.

 

Now thats something I haven't thought of! Could be. This is under full throttle or 3/4 Throttle.

 

Congratulations, what you are hearing is your exhaust flowing through the pipes. The heavy cast iron manifolds dampen this noise and you don't hear it. I don't hear it on mine because the rest of the exhaust is so loud.

We installed the 2151's on Brian's car with the stock exhaust, you can hear the same thing. He thought it was his rockers out of adjustment, I still don't think I've convinced him otherwise. All I know is that these rockers that were adjusted perfectly didn't just loosen up overnight when we installed the headers.

I've heard this on many cars with headers and it's normal, like I said you just usually can't hear it over the exhaust because most cars with headers don't run through the stock cat-back. :cheers:

 

I just remembered this, my stock duct was cracked under the duct at the TB inlet and i remenber hearing that hiss .
I would remove the duct and inspect it for cracks.

 

Thanks guys! And I will check the TB inlet too! :yesnod: