Ok I have a 2000 A4 1.8T tip and I plan on making my own exhaust system for it this summer. I will have a 3" test pipe in place of the cat and wanted to mainly know what size to make the piping of the cat-back system. I want the car to be quiet, but free up power. I know most systems are 2.5" but I was thinking what if I made it 3" with some restriction still to not only keep quiet, but keep some torque, but also let some more gases out. What do you people think??? Give me honest opinions and some help.

 

on a stock turbo 3" is too big. its will be loud if you use that big of pipe. what your saying dosent make sense
you want to make a 3" pipe but then have a bunch of restrictions. you go 3" to have no restrition

 

Well I guess in my mind what I'm TRYING to say makes sense... have 3" piping with a straight through resonator and then a more regular non-straight through muffler to quiet it down, but having the extra 1/2" will alow it to still flow better. Don't know, I thought it made some sense, I'm by no means a scientist but please just try to think about what I'm saying. LOL and don't flame me, I'm just thinking outside of the box right now.

 

if you are running a stock turbo, with 3 in you are going to lose some torque.

 

i would go 2.5in with res and muffler both straight thru's should be sufficient.

 

Is 3" proven to be lost torque/power over 2.5"??? I dont know, Im just not buying it.

 

no not less power than 2.5". but if you are completely stock and running 3 inch you don't have near enough backpressure.if you are losing backpressure and not adding more intake flow then you aren't really gaining anything


someone please correct me if i'm wrong....

 

so would the verdict be 2.5???

 

ya

 

Alrighty, thanks for the help guys I'm sure I'll be posting up about it when its getting done.