325i Exhaust - BMW Forum

M3wannabe2004 · 07-10-2005, 01:35 PM

Hey guys, I bought a new rear box for my 91 325i , the noise that comes from the back is still way to loud for my liking, heard another identical car the other day and it sounded dead quiet compared to mine. I have replace the back box twice now with a non oem backbox. The back box wasn't cheap it was costs £200 ($380). My question is can the front pipe be the culprute for the droning sound? If it's not the back box it must be the front pipe right? are there mufflers in the front section?

Please somebody, shed some light!

Thanks Guys,
Andy

kyle_baker · 07-10-2005, 05:13 PM

i'm not exactly sure of what you are asking, but i think your asking about the exhaust being loud, correct? and you have replaced the "rear box" which i have no clue what you are talking about unless you are talking about the muffler. If you are asking if it could still be loud because of the cat. converter then my answer is yes. You should try replacing it and leave the muffler. This is just hwat i got out of it since the title is about exhausts. Also if you are talking about the cat. converter then replace the O2 sensor along with it, i jsut recently replaced everything from my exhaust manifold back because my exhaust was old and the cat.s were burning out anqd my stock muffler was burning out too. You can usually smell it if it is burning out really bad. Hope this helps, but if not then please be alittle more clear and i'll see if i can help.

Angelic0- · 07-11-2005, 01:40 AM

there should be a setup like this:

Manifold -> Catalyc Converter -> Silencer -> Muffler

but the cat is optional for some, since removing it gives more power (less torque in some instances) and better gas mileage

kyle_baker · 07-11-2005, 09:08 AM

i'm not positive, but if you've replaced the muffler twice and it didn't quieten down any then if i were you i would try replacing the catalytic converter. It sounds like there is a posibility that it has been gutted out, which means that someone has simply removed all of the internal components so they can use it longer without buying a new one. There arenot really any silencers in the cat like there are in the muffler, but the packaging in the cat does end up quietening the exhaust alot more when it has not been gutted. Is the Front pipe like you say just a pipe or does it have sections in it that are larger than just a 2.5 inch pipe?If so then you have a catalytic convertoer (may or may not be gutted) but if it is just a 2.5 inch pipe all the way back to the muffler then someone ahs removed the cats for performance reason (sometimes also because of cats for a replacement cat). If the cats are still there then look at the larger sections and see if you can find any places that look like they have been welded. You are looking for a place that someone has cut the sections open and gutted the insides making them hollow and then welded back. If you find this then you really need a new cat.

Angelic0- · 07-12-2005, 01:42 PM

on a 325i there should be dual 1,75"

///M Power · 07-13-2005, 04:04 AM

To answer your question, Yet. A hole anywhere along the lineup (including the piping) can increase the sound. Ask your mechnic to look for a hole along the way. My bmw has a hole somewhere, but it sounds damn nice with a deep loud sound. I like it!

93 325i · 07-13-2005, 08:09 AM

mine is louder than most as well. When I had the stock on there everyone thought I had some crazy ass exhaust. In my case I know there are no holes anywhere, but I do know my cat is shot. Considering the age of your car this is most likely your cause as well

///M Power · 07-13-2005, 01:26 PM

It might be. But my car passed california emissions with flyign colors so i'm pretty sure it's not the cat. His problem might be the cat or the piping. Ask your mech to take a quick peek.

kyle_baker · 07-13-2005, 01:51 PM

well i'm about positive it is his cat, but when he gets a new one he jsut has to make sure he gets new gaskets, bolts, and o2 sensors or else your asking for more problems and you can get all of that from bavauto. my cat went out a few weeks ago and i bought a uuc exhaust, new cat, o2, and bolts and gaskets and it really helps the sound/performance/looks/health of your car when you do it right. He says the sound is coming from right in the middle of the car so thats most definitly coming from the cat and if the cat is stock then it probably needed to be replaced around 80,000 miles and no later than 120,000 miles, he told em he is up to something like 144,000 miles so its definitly the cat.

93 325i · 07-13-2005, 02:00 PM

^^i concur. Based on his mileage it is due. Plus I am going through the same thing, but dont mind the "sporty" sound haha.. Once I get the letter for emissions testing then I gotta suck it up and buy a cat..

kyle_baker · 07-13-2005, 05:10 PM

well you can always suck it and go with a UUC exhaust then, lol, and still have the sporty sound and performance, but a brand new system.

kyle_baker · 07-13-2005, 05:12 PM

nm, looks like you have a good exhaust (an m exhaust) but you could always come over to the uuc darkside, lol, even real M's go there, lol

93 325i · 07-14-2005, 08:06 AM

The only benefit of the M exhaust is the chrome tips. I guess it has a slightly lower tone as well, but I noticed no real gain. UUC system U seems to be the exhaust of choice.. I want to get my S50 swap done first. I came across an unbelievable deal for an S50 engine and tranny 90K miles for $2600 shipped, but I dont have the funds yet. Hopefully he'll still ahve it by the time im ready

kyle_baker · 07-14-2005, 04:05 PM

good luck man, that will be awesome.