[e92justin]

Tommorow im getting a borla muffler installed, doing 3 in. piping to the cats, taking out resonator, and secondary cats. Going to sound beasty as hell, only thing im worried about is error lights going on the dash. Will my dash start going crazy on me when i get it done?

[c_jeong89]

from what i remember the secondary cats aren't wired to the computer or anything so it shouldn't give u any error codes. I think I remember some other people doing secondary cat deletes without any errors so u should be fine.

[Gavin@MMW]

As long as you dont mess with the headers you wont get any errors

[ddigangi]

^header back is when issues arrise, but that is because you removed/disabled your 02 sensors for emissions

then you need a reflash and blahblahblahblah

[5erman]

dude you are going to notice a huge decrease in performance with 3 inch piping all the way through and no resonator. Stock piping is 2.75 inches and the RPI exhausts which are by far the most proven hp gains and some of the other exhausts actually stick with stock diameter for the most part and then taper down to a SMaller pipe diameter towards the end to keep the velocity of the exhaust gas high and fast-which is what you need to create power.

By increase the pipe diameter your exhaust gas velocity will signifigantly slow down and you will get less flow in a velocity sense-this will lose and reverse the vacuum effect of the velocity that sucks exhaust out of the cylinders and thus forces air into the cylinder more quickly-

Most people callt his "loss of back pressure"-really what people are referring to is loss of velocity with aftermarket setups-backpressure is never needed however with backpressure typically comes higher velocity since the smaller pipes that create some backpressure also flow faster-so its really mislabeling.

Anyway I would atleast keep your 2.75 inch pipes. Also the sound will be better if you use the normal pipes-slower exhaust flow will nto create as much sound as faster flowin exhaust gas.

but to each his own-people think wider is better but taht is only true for a FI car where the power is not at all dependent or effected but the exhaust gas vacuum effect since the engine is forcing air into it, not being naturally sucked in via a vaccum.

[TommyK]

i agree. 3inch is way too big for our NA cars. i mean they dont force gasses out nearly as quickly and loud as the 335 where you need to get the gasses out of there ASAP

[e92justin]

Yeah i took the car to the shop today. Guy used to make custom exhausts for BMW race cars on the track so he knew what he was doing. He told me whether i wanted 3 in. piping or not he wouldnt do it because it would be stupid. So we went with 2.5 in. piping to the cats removed the resonator and put a 4" round magnaflow muffler in place of resonator and connected pipes to dual magnaflow tips. "more" power, deeper tone, and loud just like i like it.

[DimSum]

Originally Posted by e92justin

Yeah i took the car to the shop today. Guy used to make custom exhausts for BMW race cars on the track so he knew what he was doing. He told me whether i wanted 3 in. piping or not he wouldnt do it because it would be stupid. So we went with 2.5 in. piping to the cats removed the resonator and put a 4" round magnaflow muffler in place of resonator and connected pipes to dual magnaflow tips. "more" power, deeper tone, and loud just like i like it.

What happened to the borla..?

[e92justin]

I wanted to do borla but i was kind of iffy on how it would sound on my car. ive heard plenty of magnaflows on bimmers and i like the way they sound. i know borlas have a more high pitched sound to them and didnt know if it would go right with my car. i decided to play it safe, keep my cats and go with magnaflow. has a beautiful deep tone to it.