I have an original 1991 Camaro Z28 5.0 Auto with 39K miles. Under hard acceleration I hear a whistling or hissing sound. My exhaust connections are tight. The air tube is connected. The air pump works. I have yet to check vacuum lines, but I will this evening. What could it be? Car has been excellently maintained. Recent tune up and all sensors changed and recent EGR valve changed since the original was all messed up. Still has original catalytic converter.

Thanks in Advance.

 

TBI or TPI? If TBI, did you put an open air element on? Those always give that suction/whoosh sound at WOT. Does the car idle and run normally?

 

^^^^THIS

Need more info.

 

Car is completely stock and idles fine. Tuned port injection.

 

I stated I have a Z28 which is TPI.

 

A stopped-up cat or muffler will cause a sound like that. Will also make the car have even less upper RPM power than what TPI normally restricts it to. I mention both of those parts because it's possible for the cat to break up and the pieces end up in the muffler.

 

I was thinking the cat myself. I just put a brand new Dynomax muffler on which is almost identical to a stock muffler in looks and sound. The cat has not broken up yet. I think I will change the cat. What do you recommend Walker or Davico?

 

I have no particular recommendation. Seems like I usually end up with Catco over the years which have seemed to be fine. Can't really go wrong with Walker although they aren't the "high performance" type of thing usually. Never heard of Davico.

 

I agree that the exhaust system can cause that noise when it's restricted. There is a SUPER easy test for this: Got a compression tester with thread-in hoses for the various spark plug hole sizes? Get or borrow one.


The larger hose (second from the back, in the pic) will thread right into your O2 bung. Thread the Schrader valve out of it, stuff some rubber hose over the coupler end long enough to get into the car or up to the w/s, stick a pressure gauge on the end of the hose (something with more than 10 PSI resolution, less than 100 or so) and replace your O2 sensor with your quickly rigged exhaust pressure test hose.

Exhaust back pressure should be about 3 PSI or less, under max engine output, so go for a quick test drive. Go WOT to red line, if you build significantly more than 3 PSI, you found your "hissing sound". The last time that I DID THIS TEST on a car, I had 22 PSI, just flooring it in neutral. Problem proven.

 

Thanks. I will give that a try.

 

Hissing sound went away after I changed the original factory catalytic convertor. Car feels more responsive and a little louder as well. Replaced with a Walker car which was 1/3rd the size of the original.

 

You ever test the pressure? Love to know what you were building?

 

Unfortunately I didn't. I took a chance and replaced the cat. My exhaust is new from a brand-new cat into a full Dynomax 2.5-inch system. Exhaust sounds alot better.