I am going to be doing a Magnaflow catback, car now has an aftermarket full round tube Y pipe from the last owner - its in OK shape - but has some surface rusting. I can get a dirt cheap almost brand new stock "Y".

I read a lot here that suggests there really is no flow loss on the stocker. So what do you guys think - is it worth making almost the entire exhaust new while I'm at it? (I just had one cat replaced under warranty so the only "old" part would be the PS cat).

 

no.