Exhaust System

[Tiago]

Why BMW choose 2x pipes from the engine till the rear wheels and then convert to one pipe??? Why don't they convert to one pipe after the cats till the rear??? One pipe means less weight and better flow balance.

Just think on a custom exhaust like this: 2x dp plus 1x mid-pipe till the tips with one big muffler in the center. There are very light weight mufflers like BURNS.

[boostin]

Originally Posted by Tiago

Why BMW choose 2x pipes from the engine till the rear wheels and then convert to one pipe??? Why don't they convert to one pipe after the cats till the rear??? One pipe means less weight and better flow balance.

Just think on a custom exhaust like this: 2x dp plus 1x mid-pipe till the tips with one big muffler in the center. There are very light weight mufflers like BURNS.

whats the silver metal thing about two feet before the muffler? resonator?

-Chris

[BMWeber]

maybe the first section is the same piece as the 335i and they went to one pipe at the rear to make it fit better

[BMWeber]

Originally Posted by boosted

whats the silver metal thing about two feet before the muffler? resonator?

-Chris

yes

[Tiago]

Originally Posted by BMWeber

maybe the first section is the same piece as the 335i and they went to one pipe at the rear to make it fit better

But the point is, if they went to one pipe at the rear, why not to go with one pipe right from the dp??? There are a few 335i with 2,5"" straight pipes all the way (without cats, resonators and mufflers) and the sound isn't that bad, only a bit of drowning through mid rpm range. But with a muffler at the middle it will reduce that drowning.

[Numb3rs]

Originally Posted by Tiago

But the point is, if they went to one pipe at the rear, why not to go with one pipe right from the dp??? There are a few 335i with 2,5"" straight pipes all the way (without cats, resonators and mufflers) and the sound isn't that bad, only a bit of drowning through mid rpm range. But with a muffler at the middle it will reduce that drowning.

??
A car exhaust is there for a reason, with biturbos, it would be too restrictive to run a single pipe after the DP's. Again, the restriction would hinder the N54 and the added turbulence would further disturb the exhaust flow. There are two secondary cats, which is better than a single one. Isn't that obvious?

Additionally, "drowning" is not the correct term, it is drone 'ing. And a second muffler will not correct it because the drone is a resonance or frequency inherent in a design of an exhaust, not because of the noise.

The reason you replace a BMW engineered exhaust for an aftermarket one is because you want a less restrictive exhaust. That is hard to do and most aftermarket exhausts have gains ONLY when you remove the cats. Which is illegal, unless the aftermarket exhaust has been CARB/EPA certified.

[Tiago]

Originally Posted by mikeo

Numb3rs, maybe you should respond to Tiago in Portuguese to better point out his English language deficiencies.

What i need now is that you explain me better your perfect english.

1. From my experience, the E46 M3 has a two pipes from the engine to the rear. Supersprint smartly made one 3" pipe from the cats till the rear. With this they eliminate the x-pipe because the balance of the exhaust flow is now made in that one big pipe, and at the same time they saved some weight from the exhaust system.

2. It is obvious from the pic that i posted, that BMW converted to one pipe at the rear because of the lack of space, and by this they don't need an x-pipe in the 135i, like the 335i that has a two pipes all the way but with an x-pipe at the center for the reasons that i mentioned above.

3. If you are searching for the highest hp possible with money wisely spend, i'm suggesting with this thread a catless DP (like UR ~$600), then go custom with one 3" pipe (eliminates the 2nd cats) till the rear with one aftermarket muffler at the middle because is where you have more space under the 135i for a conventional muffler. For a less radical guy and to go really cheap, think in a 3" pipe at the middle (still eliminates the 2nd cats) till the oem rear muffler. I bet that a custom pipe like this won't go above $250, and the most restrictions of the exhaust flows is in the cats and not in the mufflers. My option 1 (fast and furious) is just for the weight savings freaks.

[mikeo]

Tiago,
I felt Numb3rs was rude to point out your minor misuse of a word. I think your English is just fine for a 2nd language and I can understand your meaning with no problems.

To answer:
1. Agree. The main advantage of a single 3" in most applications is weight savings. In the E46 M3 it also helped with the 'rasp' sound issue.

2. Agree completely.

3. Agree, and I think we will see the single 3" from downpipes back either from an after market company or likely first as a custom exhaust by a private owner. Maybe you? Should be worth a try.

Some people may not want to eliminate all the cats on a street car, or even one pair, for legal or pollution reasons, which is understandable.

[J-Sud]

on the picture...correct me if I'm wrong...i see what i think to be 2 secondary cats down to 1 resonator then to the rear muffler.

Are there still "primary" cats on each down pipe that we cant see in the picture?

Thanks

[Italteen3]

Originally Posted by J-Sud

on the picture...correct me if I'm wrong...i see what i think to be 2 secondary cats down to 1 resonator then to the rear muffler.

Are there still "primary" cats on each down pipe that we cant see in the picture?

Thanks

That is correct the primary cats are on each DP.

I've heard most people who eliminate the first set of cats with catless DPs, and keep the secondary set have still passed emissions tests. Imagine Titanium exhaust setups! mmmmm the weight savings.

[BoostFrenzy]

what diameter are the downpipes and when they become one what diameter is that? if two 2.25" pipes end up in one 2.5" or 3" single pipe further down the exhaust stream, it's better than coupling the hotsides of the turbos with 2.5" or 3" to begin with

[Italteen3]

Originally Posted by BoostFrenzy

what diameter are the downpipes and when they become one what diameter is that? if two 2.25" pipes end up in one 2.5" or 3" single pipe further down the exhaust stream, it's better than coupling the hotsides of the turbos with 2.5" or 3" to begin with

DPs are 2.5".

[J-Sud]

Originally Posted by Italteen3

That is correct the primary cats are on each DP.

I've heard most people who eliminate the first set of cats with catless DPs, and keep the secondary set have still passed emissions tests. Imagine Titanium exhaust setups! mmmmm the weight savings.

so i take it that the primary cats are higher up on the DP to there point we cant see them in that pic....are there any pics of the the primary cat and DPs?

[Brian Paddock]

Originally Posted by J-Sud

so i take it that the primary cats are higher up on the DP to there point we cant see them in that pic....are there any pics of the the primary cat and DPs?

Here are some that I took.

[J-Sud]

thanks..


those primaries are a lot higher than i thought they were...

[BMWeber]

Originally Posted by Tiago

But the point is, if they went to one pipe at the rear, why not to go with one pipe right from the dp??? There are a few 335i with 2,5"" straight pipes all the way (without cats, resonators and mufflers) and the sound isn't that bad, only a bit of drowning through mid rpm range. But with a muffler at the middle it will reduce that drowning.

I'm a little late her but I was thinking if the front section is the same as the 335i the reason they didn't just change the whole system to one pipe is cost. not that one pipe wouldn't be cheaper but the two pipe system is already in production so no new tooling costs and its a very high volume part. where tooling up a new system just for the 1er especially with the lower production of the 1er would be very expensive in comparison.

[jeremyc74]

Originally Posted by Tiago

But the point is, if they went to one pipe at the rear, why not to go with one pipe right from the dp??? There are a few 335i with 2,5"" straight pipes all the way (without cats, resonators and mufflers) and the sound isn't that bad, only a bit of drowning through mid rpm range. But with a muffler at the middle it will reduce that drowning.

One thing that I can think of is the exhaust gas turbulants might have caused an issue. It may be that a longer section of pipe was need to allow the gasses to smooth out before entering the converters. That could be why the converters are back so far, and then the additional length of pipe between them and the muffler was just the smoothest way to make the transition to one pipe. It's also possible that they needed to get the converters away from the engine bay because of heat control.

Also since the turbos are each being fed by 3 cylinder, they will be pulsing with the exhaust strokes. Maybe there was an issue with that pulsing that caused problems between the two turbos, and required the longer lenths of pipe.


These are just guesses. I'm no exhaust or turbo expert.

[F0Bman]

I believe for space considerations, if you look at the undercarriage if there was another resonator/catalytic converter it would disrupt the airflow from underneath.