Restrictive Stock 323Ti exhaust: Options without going Aftermarket
 

First, sorry if this question is worded awkwardly at times, but I don't know a lot about the topic and I know the 323Ti is not discussed here as much as the 318Ti (fittingly so, as it is a EU market car).

I have a loud rattle from the underside of my 323Ti and am heading to the mechanic in the next few days. Should my inclination be right that it is something from the exhaust I figured this would be a good time to address what I have heard is the very restrictive stock 323ti exhaust (2 exhaust pipes are joined to 1?).

http://bmwfans.info/parts/catalog/E3...ront_silencer/

I don't want a aftermarket exhaust becuase I don't want the car to be louder than stock (think long Autobahn trips). However I'm all for less restriction and a little more HP and TQ if possible. Can anyone suggest what they would do, or what they know about this topic? Is a custom stainless job of 2 pipes to the muffler and two out or Y-pipe the best choice? stick with stock dimensions or slightly larger piping?

T.I.A.

That part in the diagram you linked to is the catalytic converter. As you can see, the 2 to 1 decrease happens just prior to the cat, so anything you do from there back probably isn't going to make too much difference assuming you intend to keep the stock cat in place. Theoretically you should be able to replace all of that with the parts from a 328, but you might need everything from the headers back and that would probably be very expensive. The sedan mufflers will fit on the ti, assuming you have a creative muffler guy. See the diagram below for reference.
http://bmwfans.info/parts/catalog/E3..._lambda_probe/

BTW, your rattle is probably related to part number 8 and its associated pieces in your diagram. Those tend to deteriorate and allow just enough movement of the pipes there to rattle against the remnants.

I have a Remus 6cylinder exhaust on my TI. It does fit, but the tail pipes stick out a lot no matter what you do. It does sound great though. It also had to be custom welded

Common mod for the sedan/coupe guys is to grab a 325i or 328i exhaust system and just bolt it onto a 323i. For a compact just do the same and get it shortened/modified slightly to fit a Compact.

^That's an idea I was thinking of/heard about. How much of the exhaust do they take from the 328? Being OEM it should be a nice solution to the restrictiveness of the 323 exhaust while keeping the car quiet or OEM.

To be honest got no idea how much they would take out, just give it to an exhaust shop and they should be able to sort it out to the right length.

^ Oh no, I meant how much of the 328 exhaust would I need, as in, if I found one for sale or in the junkyard, how much of it would I need to make sure to get? (i.e. just from the cat back)

You'd want the complete exhaust ie; midsection(catalytic converters) as well as the rear section(catback). The midsection should bolt right up to your car without modification. The rear section will need to be shortened and have new hangers welded to the backbox(muffler).

This will give you a true dual exhaust from the exhaust manifolds back.

^Awesome, thanks Cooljess. I found these two for sale in a neighbouring town. From the pics, am I right that they would be the compelte sections I would need?

Also, when people talk about the 323Ti exhaust being restrictive, what kind of or how much of a difference am I looking at by switching to the 328 exhaust? I ask, because now I am doing this purely for driving pleasure/a little performance. My initial problem back in Novemeber has been long solved, just a minor rattle I had removed.

T.I.A.

Significant difference.

The M52 B25 motor in your car is basically a revised M50TU B25, the engine that came in the E36 325i which is rated from factory as 141kw in power whilst your 323ti motor is rated at 125kw.

BMW restricted the M52 B25 motor by fitting a single exhaust system similar to that in the 4 cylinder cars and fitting a more restrictive inlet manifold. If you change the inlet manifold to one out of an E36 325i/E34 525i and do the 328i exhaust manifold swap together you will have more power than a standard 325i which should make your car pretty rapid.

The exhaust is the most restrictive part on your engine so there will be a significant bump in power and torque across a lot of the rev range - about 5-10%.

To be honest, after looking at the pics, you may have a difficult time fitting the 328 catback under the ti's chassis due to the "bend" in the muffler itself. I believe ours are straight. You can look at your current muffler and see if it has a bend. I know many 323i/323is owners have done this mod, but I can't recall seeing any 323ti's with it since we only got 318ti's here in the states. I would imagine you'd get about 10hp give or take, who knows, maybe more.

^Wow, thanks to both of you for the insight/info. I am definitely going to look into trying to fit a 328 exhaust considering the potential it has, and the fact that the M50 manifold was one of my planned mods to carry out before the spring. The coupleing of the two sounds super.

Cooljess, I'll get under the car this weekend and take a look at the exhaust to see where I stand. I'll report back so that the info. is out there if the 323Ti differs from the 318Ti in this area. I wonder if Realoem would have a diagram that would give an answer? I'll have to take a look.

sometimes realoem's illustrations are inaccurate due to them sharing drawings with other vehicles in that series.

Maybe a 328 midsection paired with Z3 catback is the solution:
http://www.318ti.org/forum/showpost....1&postcount=46

There are some problems that have to be mentioned :)

First the car will be driven in germany and the german law for cars is very, very restrictive.
Shorten the catback? Now way... No TÜV (Organisation where there cars have to be checked every two years by an mechanical engineer or skilled master of mechanics, these guys are nearly officials and mostly are relativly strict) validator will allow such a modification.

The only way to get a complete two-piped exhaust system is to use the 328 cats and the Z3 2.2i oder 3.0i catback. Than you have to build an 20inch bridge betweet cats and catback.

You can see it here
http://h10.abload.de/img/cimg1800rora6.jpg

This is my exhaust system on my 328ti.

The results are a better exhaust gas stream because of the metal cats and the two-piped system and maybe 3-5hp. More is not realistic, because the main restriction at the M52B25 is the manifold.

These values are proven by one of the leading M52 experts here in germany ;)

But i also have to mention that the sound then is "a little" louder than the stock exhaust system
http://www.youtube.com/watch?v=u6ZEE2G79I4 (my Ti with the above described system)