hissing noise after decat

Is it normal to have a bit of a hissing noise after a full decat? I have ran my car with a nur spec R and a first decat for years now and all was ok. Today I fitted a second decat pipe (thought I might as well try it ) and now when the second turbo comes online I can hear a hissing noise. Could it just be the noise of all the exhaust gases getting pushed out the exhaust when both turbos are online? I dont get the noise below 4k rpm.

I dont think I have a boost leak because my EBC reads very stable boost at around 1bar which is where it's supposed to be, plus I had no problem before fitting the second decat. I have no smoke on start up or on full boost and I have remade all the exhaust joints with new gaskets and paste twice incase it was one of those.

Apart from the new noise (which is not that loud but was not there before) everything works fine.

if its hissing you either have a leak on the joint or the rear exhaust box has a blockage ?

I have the same noise when i ease off after giving it some....always thought it was the gase's escaping abit quicker:d

Still does it with new exhaust ( 3' Decat's as well ) fitted

Guess i will get mine checked for any leaks on the joint as well:)

I dont think its anything to be concerned about but I did think it was a leak on one of the exhaust joints so I remade them again with new gaskets and plenty of exhaust paste. I must admit the second time round the noise seemed to be less noticable (although I could have been imagining it ) but I made sure that all joints were made spot on.

I dont think I have a boost leak as boost is stable and where it should be. The only thing I changed was removing the second cat for a de-cat pipe. I was just wondering if it is normal to get a little noise like this after removing the cats.

the ebc controls the boost pressure so i would expect it to be stable even with a small leak. If the pressure is being released a little the ebc will control the actuator to compensate. I would think anyway.

the ebc controls the boost pressure so i would expect it to be stable even with a small leak. If the pressure is being released a little the ebc will control the actuator to compensate. I would think anyway.

I know what your saying and I suppose this would be the case if I had it turned on but I left it off while I was checking things out. To be honest I hardly ever use it. The car runs at about 1bar now with full decat and rr and I only use the EBC if there is something fun to play with but as for boost pressure, it was very stable under heavy acceleration with the EBC off. I did have a boost leak about 9months to a year ago and the boost reading was all over the place and even the EBC couldnt keep it very stable so I am quite sure the noise isnt from there.

I'll just ignore it for now and see if anything occurs but I think it must just be a slight change in the sound of exhaust gas flow or something.

I know what your saying and I suppose this would be the case if I had it turned on but I left it off while I was checking things out. To be honest I hardly ever use it. The car runs at about 1bar now with full decat and rr and I only use the EBC if there is something fun to play with but as for boost pressure, it was very stable under heavy acceleration with the EBC off. I did have a boost leak about 9months to a year ago and the boost reading was all over the place and even the EBC couldnt keep it very stable so I am quite sure the noise isnt from there.

 

I'll just ignore it for now and see if anything occurs but I think it must just be a slight change in the sound of exhaust gas flow or something.

So you replaced the 2nd cat with a de-cat and didn't see any increase in boost pressure? That seems strange, i know it doesn't make the same difference as the 1st cat but you should see 1psi or 2 if you haven't upped the restriction any.

Takes me back to a leak

I changed the rr to a smaller one when I took the cat out. Its from whifbitz and made to give about 1bar boost, which it does almost spot spot on.