Does adding a HFC replacing just the stock cat pipe require a re-tune? I would not be replacing the downpipe.

 

Yes it would be best to get one asap

 

Require: No
Suggest: Yes, What other mods do you have/want to get?

 

At the very least, retune BWG turbo control. There is significant back pressure due to the stock cat that had already been tuned in. Reducing back pressure without retune could result in turbo overboost unless other tuning safeguards aren't disabled and configured to perform effectively.

 

No it is not requied for just a high flow cat.

 

As stated above: not required, but you will see more of a gain by tuning.
Either way, less back pressure for the turbo is a good thing. 👍

 

If not protuned afterward, overboosting from reduced back pressure may compromise engine health. Do you intend to keep the car or to flip it in a few years?

 

Car will not overboost without tuning despite some opinions posted. Boost will come on quicker than your ecu map is expecting and error correction will kick in and reduce WGDC as required.

As stated - required = no, but you will get more out of it if you do. If you have more mods planned in the near future I would just wait. You will not damage your car

 

I think it really depends on how you drive it. Shouldn't have a problem if you drive it normally until you get your tune