i just had Borla TD exhaust and Stillen test pipes installed and as the RPMs drop i can hear a hissing sound. Does anyone know the reason for this and whats the cause of this? im guessing its the test pipes?

 

Its the test pipes mated to a large diameter exhaust. Its normal and it happens to everyone.

 

if its an intermittent sound (i.e. hisssss.....hisssss), then it might be an exhaust leak. just check your connections and retorque them.

 

Probably a minor exhaust leak.. I just installed mine and I have a minor leak. A little tightening should help.

 

I don't know what it is. I guess I have to go back to where I got it installed. But they reved it and listened to it but didn't say anything. I would say it kind of sounds like the noise when you miss a gear. I don't know how to explain it but it sounds like air being released as the rpms drop towards the front of the car

 

Go to a local Z meet. Somebody would know right away what the noise was from.

 

I hear the same noise every time i let off the gas and its nothing to worry about unless it really is as loud as you say (like a gear grind). But otherwise i'm pretty sure its because of the loss of backpressure and the fact that the test pipes let soo much more exhaust through than the stock cats. With mine i first thought i had an exhaust leak and threw it back on the lift and checked and re-tightened everything and it still happens its just the test pipes

 

I went back to the shop and they told me its just the sound that he test pipes make bc they're not resonated but I had them clog it to leak test it anyway and there's no leak. I guess I was just worried bc I bought the borla td exhaust and the stillen test pipes used and kinda cheap but they assured me everything was normal. so I got a nice exhaust set up for less then $600 installed