High flow cat or decat....that is the question.

I'm Just Rob.

Moderating or something,
Staff member
Moderator
VCDS Map User
Gold Supporter
One for all those clued up on the subject really.
Which is the better option for reliable performance and no engine management issues .
I currently have an 034 HFC with custom larger bore down pipe to suit the cat and oem exhaust system.
No issues with engine management etc and car runs really well, I run VCDS weekly and nothing is amiss in this dept.
If I went with a De-cat large bore down pipe combo am I more likely to have issues due to the lack of a cat being in place.
Both setups use fore and aft lambda sensors , how well would the ecu deal with the lack of a cat , would it still adjust things based on info received from both sensors even if the cat was omitted or would the parameters be way out for it to compensate.

any feedback would be greatfully received chaps.
 

Dan_Avant

Registered User
I've always been under the impression a decat will yield more power but you will need a map once fitted as it will cause issues for the ECU. Will also cause issues for you come MOT time as it will likely fail the emissions test.

Personally a I'd stick with what you've got, it works and your getting pretty decent power/torque figures.
 

I'm Just Rob.

Moderating or something,
Staff member
Moderator
VCDS Map User
Gold Supporter
The phrase " if it's not broken " comes to mind really.
As you say probably best to leave well alone , the old bus it running really well now, otherwise it will only go tits up ...
 

BennyG_UK

Top Gear
VCDS Map User
My 2.0t has no cat. No issues at MOT time, but I have a very friendly tester who turns a blind eye. They aren't around everywhere though. I kept my old cat just incase (its actually currently in Essex out on loan to help a fellow member of the A4 club).

If your childish like me and want over run pops and bangs, then decat is a must otherwise you'l kill it.

You can also get a lamba spacer that will move the sensor more outside the flow. This sometimes allows you to get away with no error codes for not having a cat
 
Top