Catalytic Converter Airtrek

The catalytic converter on my Mitsubishi Airtrek Turbo has fallen to bits and is rattling. To replace with the factory unit will cost more than the car . Have been told that a straight pipe can be fitted and get rid of it completely or fit a resonator .Any downsides of these options .Any help would be appreciated.

http://vehicleinspection.nzta.govt.nz/virms/in-service-wof-and-cof/general/exhaust/exhaust-emissions

Your best bet would be the local car wreckers.
Probably won't need to be exactly the same model or brand but as long as the converter is the same or slightly bigger & fits in the gap properly with the same sensor connections, then it would do the trick ok.

If you want a replacement Cat ,try Chase Autos.

i did not read the lnk in post 2 i know what the rules are.
there is a cutoff date where you are no longer are allowed to remove the emission items , i recall my 07 passat is before this date .
The rule is you are not allowed to remove any emission divises after this date .
This means technically you can not fit a straight pipe to any vehicle now since this date has passesd.
But you where allowed to up to that date.
So if your car was built before that date then no one can proof that the emission divise was not already removed before the law made it illegal.
Do you understand what i am telling you?
if your car is built after the law was passed then its 100% proof that you could not have removed it already before the law came in to effect.
Now there is more
If you remove the crumbles of the catalisator then the cat becomes essentially a straight pipe and still looks as if it has a catalisator.
.The problem you can run in to are as following.
Some manufacturer build in the emission coding obd2 a catalisator efficiency monitor. if it fails it will light up the check engine light .
that would be how they would know you have a bad cat if somone pulls this code . something like "catalist efficiency below threshold"
now the next problem would be if they introduce exhaust emission testing it would also show up as not meeting the emissions at tailpipe.
Other then that no one will be the wiser if you have a empty cat

Are you sure its not the heat shields on the outside rattling that have come adrift

Now to how the engine computer knows the catalisator is ineficcient.
You have a oxigen sensor or air fuel ratio sensor on later models .
This sensor mesure the oxigen content in the exhaust and send a electrical voltage to the computer for data to process.
One befor the cat and One after the cat .
The one before the cat sending the same voltage as the one after = no oxigen is stored in the cat= its either not existing or is inefficient and check engine light turns on.
Now you can not just put a resitor in there as the o2 sensor creates a voltage up and down rich lean rich is less air lean is morer air.
The computer comands more or less fuel to cause these conditions to light the cat loads of fuel and then loads of air and then it starts switching air fuel in to the exhaust to keep the fire going in the catalisator .
Thats how the cat works a bit like your log fire only way faster with air and unburned fuel.
The only way to not have a check engine ligh if it has catalist efficiency monitoring ,
would be to tune the ecu map to command it no longer to add fuel and air in exhaust.