As above really how restrictive are they i have a group n backbox would it be worth me putting it on when i get the car remapped would it make any difference but will still have the sports cat on .

thanks for any help on the above.

 

Changing back box will give the least power gain of downpipe / centre / BB change. Biggest effect of changing BB will be more noise

 

It will make NO diffrence from a group N IMO.

 

When Andy F mapped my car he mentioned that they were a bit restrictive. Will depend a bit on how far you are going mods/bhp wise (eg over 300bhp). Don't know nowt about the Group N tbh.