I own a 2000 Z28 and it seems to me that every time the car shifts a "blow off valve" type sound is coming from under the hood....it is easliy heard from the inside of the car....anyone know what this is?

 

One of those $40 blowoff sound boxes on Ebay.

 

could just be intake noise.

 

thanks ***! I am being serious here! So unless you know what it might be then don't put your two sense in. Thanks and have a good day!

 

Hey Spy. Well I looked into that and found no leaks or backpressure problems...It only happens when the car shifts gears and it is loud...people who hear this when I pull up think I'm tubo'd when I'm stock....I just hope it's not doing anything harmful to my engine

 

I have developed the same noise.When I let off after a WOT blast it does it.I don't know where it's coming from either. At first I thought it was a belt or something but that doesn't make sence.My QTP cutout whistles a little under wot, mabe it does the blow off sound too.
Keep us posted.

Jay

 

I've got the same year car and am noticing the same thing. I started to notice it after I installed my lid. I never noticed it before, so my guess is it's either the air hose and the breather filter...or better air flow going into the throttle body since I replaced the restricted air box assembly with an after market lid. That's all I can come up from it. Other than that, I dunno.

 

Just sounds like intake noise to me.

 

i had that some problem but found out it was the air pump with the aftermarket lid. then car got warm and it stocked.

 

oops stoped not stocked

 

Check for any leaks in the PCV system? That's where the pressure builds up. Could just be intake noise as well though like everyone else said.

 

yeah it most likely is intake noise but the thing that sucks is it only does it under load so I can't just park it and let the engine run to allow it to happen, so we'll probably never really know what that sound is...as long as it isn't cauing any harm to my engine or it's performance I can live with it...but if there are any people out there that may know please feel free to input...it's goood to get the ideas flowing

 

If you hear it at WOT it could be valve flutter. I know every once and a while at WOT when I get it up to 6k my valves float and it's very audiable. It, to the right ears, could sound like a BOV.

 

well it happens when I am driving normal and don't have to have my foot on the gas...it happens just as the car is shifting gears ( I have A4) It's louder when the engine is hot than when it is cold

 

do u have any sort of tranny mods? a few cavalier guys who were running high tranny line pressure would get the same noise when there car would shift. sounded like a bov when the car was under load, and the tranny shifted.

 

There are no mods done to the tranny or car what so ever...The car is completely bome stock. I've had the car checked out by mechanics as well and they can't seem to find a problem...they say the car is mechanically sound....

 

Actually think that would be kinda cool to have

Always loved that blowoff sound on turbo cars. Would kinda dampen things if it was hurting something though.

 

Yeah, I went on another drive in it today and started looking at other parts of the car and noticed that when it did "blow off" my lights would also flicker at the same time

 

i have the same thing....intake noise

 

Same thing here as well. Only hear it though right after lifting from WOT. But not all the time, only occasionaly. Even at speed it is loud enough to here over road and engine noise. Sounds like a burst of air pressure releasing suddenly from somewhere under the hood. Have had the car for 8 months or so. First noticed it a few months after I purchased the car. Cannot remember for sure if I noticed it before the lid was installed.