my cat is starting to rattle ( hunny comb is falling apart) and was thinking of just hallowing out my cat, and this was also sudjested by my friend also. My concerns with this is will it make my exhaust sound too loud (also have a borla cat back) and will this make me fail emissions? thanks for all the help 99.5 A4 1.8t Qm


-Tyler

 

you would need to do the sparkplug fowler mod co the cel dosent come on
you wouldnt fail emmisions
it would make it louder

my vote, just get a hfc

 

if you live in california, or any state which uses emissions standards as strict as california's, you WILL fail emissions. the catalytic converter does 3 things that help you pass emissions tests. those 3 things are:

1. Reduction of nitrogen oxides to nitrogen and oxygen.
2. Oxidation of carbon monoxide to carbon dioxide.
3. Oxidation of unburnt hydrocarbons to carbon dioxide and water.

when you hollow it out by removing the "honeycomb" crap, the cat basically becomes nothing more than an expansion chamber. ditto lazer viking, get a high flow cat, and you won't have to worry about emissions. you'll also experience nearly all the added power that a test pipe gives you.

 

Get a test pipe, a hollowed out cat will cause turbulence defeating the purpose...

SMo'

 

I say go for it if youre trying to pinch pennies. Wont have the same performance increases as a test pipe, but it would make a difference.

 

Good point!

 

If it is rattleing check the heat shield that goes around the CAT, as well as the one on the body of the car (if there is one)...

SMo'