i have an 02 sti type UK with the following mods

RCM Induction Kit
Forge re-circulate BOV
De-cat centre section
Resonator pipe removed
Scoobyworld backbox
Uprated discs and Pagid Blue pads with braided hoses
Lowered Eibach springs
Just about everything from the Whiteline catalogue for a scooby
18'inch white speedline GT Ones

Can I change the downpipe for a high flow cat downpipe without the need for a remap or CEL reset, also is it wirth changing the headers an up pipe for a equal length set up. Any advice/opinions would be a big help.

 

you will need a remap if you change the downpipe, also by remapping you will get the full potential from your mods..