exhaust setup question

[tranquility]

30i has the dual exhaust to one side while the 35i/s has 2-sided single exhausts, but all 3 trims have the same basic engine (sans turbo &/or tweaks, of course). Question is which the more efficient setup and why?

[jparnes1]

30i has a single muffler/twin exhaust. 35i/s have 2 mufflers each with one exhaust. Stands to reason that the N54 is getting it's exhaust vented with less restriction.

[CedarZ4]

Just as a minor clarification, the 30i only has a single exhaust but with a dual outlet (essentially, it's just for aesthetics).

In regards to which is more efficient... it's hard to say but considering how both the 30i and 35i have same diameter exhaust (i.e. piping), that would mean the dual exhaust would allow for a greater free flow, thereby theoretically improving performance. However, then you have to take into consideration the added weight of a dual exhaust system. In the end, I think performance is negligible between the two, the only real world difference is aesthetics (exhaust pipe on 1 side vs. 2) and most importantly, sound.

In terms of "efficient" as you put it, I think the 30i is more efficient in that it is lighter weight, a cheaper system to replace/build, and on such a small engine, I think the increase flow from a dual system is negligible.

[tranquility]

Actually, I'm confused about the I6, because the cylinders are all to one side, why bother w/ two pipes going to the back (I think I saw the underside once, could be wrong) instead of just 1? It's not as if it's a V6 w/ 3 cyls each side? Maybe I'm way off-base here, just drawing from memory.

[CedarZ4]

You bring up a good point. I've never actually seen the underside of a Z in person (I saw a picture of it once upon a time) so I don't know how the exhaust system is set up. Traditionally, dual exhaust systems are used so one bank of cylinders can go to one side while the opposing bank goes to the other (like you mentioned). This would work for an inline engine as well, as long as you have more than one manifold. This would again provide for more free-flow for the engine. Although, more often than not inline engines only has one manifold, which would mean the dual exhaust system is purely cosmetic.

I'm not even sure if the Z is a "true" dual exhaust system in that there is more than one manifold or not. If there is in-fact only one exhaust manifold, then the dual system is purely for aesthetics and sound with no performance increase whatsoever.
Though I can't confirm because I've never seen it myself, I would bet the Z had only 1 manifold and therefore not a true dual exhaust. That is, 1 manifold goes to 1 pip, then it is split into 2.

Going back to your initial question, this would make the 30i a much more efficient system than I thought in terms of performance and performance alone.

[jparnes1]

I may be talking out of ignorance, but doesn't each turbocharger have it's own exhaust manifold?

[CedarZ4]

Traditionally, that is the case. However, if I'm not mistaken I think inline engines may be able to have one manifold despite being twin-turbo. Not sure which is the case for the Z.

This got me interested so I went on RealOEM. It's hard to tell because of the lack of description for the part #, but it seems like both the 35i (N54) and the 30i (N52) have two exhaust manifolds, as there are 2 part numbers for both.

Additionally, I went and looked up the 28i (N20) and it only had one manifold part # listed, which makes sense since this is a twin-scroll single turbo as opposed to the N54 twin-turbo.

Someone with more knowledge feel free to chime in, but I think you are right jparnes1.

I stand corrected.

[tranquility]

A picture is worth a thousand words, so here's a link:
http://e89.zpost.com/forums/showthread.php?t=360183

To my extremely layman eyes, does that mean the 35i/s has 2 exhaust manifolds? I don't think I see any X-piping...if that's the case, why not?

Are your answers as to which is more efficient affected due to the pix?

[Asbjorn]

Both the 30i and 35i(s) have true dual exhaust systems, the only difference being that with the 30i system the muffler is somewhat shared (which could also be said for the new M4 and 1-series M coupe btw).

Anyway both the 30i and 35i systems have two manifolds, four cats and no x-pipe (unlike with the M4 system which has an x-pipe). An x-pipe would have changed the sound, possibly for the better depending on taste.

(Edit: What I wrote here turned out to be slightly wrong) In terms of performance the important part would be the down-pipe cats though. In the M4 and 1M they implemented race-cats from factory. Not so much in our cars... but everything else being equal, having two cats in parallel is always better than having just one. (/edit)

N55 equipped cars do not have true dual exhaust systems because they only have one manifold and one turbo charger. It may look like a more cost effective system, but then you would have to increase the pipe diameter and cat-size to get similar performance, which I believe they did with for instance the M135i.

BTW I now realize why the left muffler is so much bigger than the right muffler on the 35i/s. It looks as if they just used a slightly modified muffler from the 30i and only made a new one for the right side. Then they probably just took out some of the dampening material on muffler for the 35is and called it a day.

Here are the 30i manifolds for reference.

http://www.realoem.com/bmw/showparts...39&hg=18&fg=10

[tranquility]

Ok, so the 35i/s must have 2 manifolds because they have 2 turbos. How come the 30i has 2 manifolds as well despite not being turbo'd (vs the N55 which only has 1)?

Also, presumably race cats are better than what we have as OEM? If so, that's another area they skimped on us, despite our cars being more expensive relatively in the BMW lineup. Arrgh, so annoying.

[Gunzaro]

The N52 engine in the 30i is a 6 cylinder engine - the exhaust manifold (extractors) are a 3+3 design hence dual outlets.

And you can't expect race cats on a non-M car! I got race cats in my AR downpipes and they aren't cheap but they do make the car sound great!

[tranquility]

I don't buy that non-M can't have race cats. That division has SUVs for christsakes! M division is not the M of old. Lousy BMW makes us pay a premium for inferior parts, so annoying.

[nicknaz]

Originally Posted by tranquility

I don't buy that non-M can't have race cats. That division has SUVs for christsakes! M division is not the M of old. Lousy BMW makes us pay a premium for inferior parts, so annoying.

Vote with your dollars and buy Porsche or Corvette next time

Why are you assuming the OEM parts are inferior just because more power can be made using aftermarket parts? Aftermarket doesn't worry about long term durability, or managing heat from sustained high speed driving, or laws about emissions and noise, etc etc etc.

[Asbjorn]

Originally Posted by tranquility

Ok, so the 35i/s must have 2 manifolds because they have 2 turbos. How come the 30i has 2 manifolds as well despite not being turbo'd (vs the N55 which only has 1)?

Because it is a BMW engine and BMW knows how to make awesome I6 engines. BTW this is actually where you get something "extra" with a Z4 compared to a 1-series. The previous gen 330i, 130i and 135i (N54) did not feature true dual exhausts. What they had instead was this:



Which is a more silent system than what you get with the Z4 30i. The front silencer is also there in the 1-series M coupe, but modified so that it has no actual silencing effect.

With the N55 you don't get a choice, because it is a single turbo system. However, due to the twin-scroll principle the two banks still can't "see" each other, so it is ok.

[Asbjorn]

Originally Posted by nicknaz

Why are you assuming the OEM parts are inferior just because more power can be made using aftermarket parts?

Please note that OEM race cats exist. That is what you get with for instance the 1-series M coupe. (EDIT: turns out I was wrong, please ignore. The prices below are still correct though...)

Let us have a look at some down-pipe cat part prices:

Z4 35i/35is - €703 (zyl. 1-3, OEM regular cat) - link: http://www.etk.cc/bmw/EN/search/sele...81/18327848041

1-series M coupe - €844 (zyl. 1-3, OEM race cat, +20% extra cost over Z4) - link: http://www.etk.cc/bmw/EN/search/sele...81/18307647042

M135i - €1081 (larger cat, but only one is needed) - link: http://www.etk.cc/bmw/EN/search/sele...76/18327602269

[Asbjorn]

Originally Posted by tranquility

I don't buy that non-M can't have race cats. That division has SUVs for christsakes! M division is not the M of old. Lousy BMW makes us pay a premium for inferior parts, so annoying.

To be fair, you also didn't get OEM race cats with the 335is. (edit: in fact you didn't with any N54 cars, M or non-M)

Anyway, while the lack of "M" components in is-cars may annoy some, here is why I voted on the 35i with my money

* You get the same DCT transmission as in the previous M3. And it is awesome.
* You get almost the same engine as in an M-car (the 1M), all you have to do is flash the ECU and add an aux water cooler (or just avoid the tracks / going WOT for too long). (to be fair the 1-series M coupe also has an 11% lighter fly-wheel and a larger cooling fan)
* You get the same engine as in an is-car which costs 100.000 rmb / 16.000 usd more here in China, all you have to do is flash the ECU.

[nicknaz]

Originally Posted by Asbjorn

Please note that OEM race cats exist. That is what you get with for instance the 1-series M coupe.

Let us have a look at some down-pipe cat part prices:

Z4 35i/35is - €703 (zyl. 1-3, OEM regular cat) - link: http://www.etk.cc/bmw/EN/search/sele...81/18327848041

1-series M coupe - €844 (zyl. 1-3, OEM race cat, +20% extra cost over Z4) - link: http://www.etk.cc/bmw/EN/search/sele...81/18307647042

M135i - €1081 (larger cat, but only one is needed) - link: http://www.etk.cc/bmw/EN/search/sele...76/18327602269

sorry, how are we sure that is a "race cat" Just seems like a different part number because the fitment in the engine is a bit different?

[Asbjorn]

Originally Posted by nicknaz

sorry, how are we sure that is a "race cat" Just seems like a different part number because the fitment in the engine is a bit different?

Great question. It says on page 16 of the technical training pdf for the 1-series M coupe that "the design of the the primary catalytic converters is the same as for the N54B30T0 on the BMW Z4 sDrive35is except that the flange position is different.

http://www.1addicts.com/forums/attac...2&d=1396203865

So I was wrong. The misinformation seem to originate from HP Autosport:

http://www.1addicts.com/forums/showp...9&postcount=22

http://www.1addicts.com/forums/showp...0&postcount=35

Now, since we know the downpipes for 35i and 35is have same part numbers, the 1-series M coupe basically uses the same primary cats as a 35i... so thank you for asking

[rking117]

this is the diagram of the 3.5i exhaust. system


and here is the one for the 3.0i


clearly two manifolds

[Asbjorn]

Originally Posted by rking117

this is the diagram of the 3.5i exhaust. system


and here is the one for the 3.0i


clearly two manifolds

Yup, and please note that part number six in the first diagram and part number nine in the second are not actually installed from factory. It is just one long pipe instead. No cut.

[nicknaz]

Originally Posted by rking117

this is the diagram of the 3.5i exhaust. system

and here is the one for the 3.0i


clearly two manifolds

My GUESS is that the decision to go from exhaust outlets on 1 side vs. both sides is a ///Marketing driven one, to show a visual difference between the trims/engine power levels

[tranquility]

Originally Posted by nicknaz

Vote with your dollars and buy Porsche or Corvette next time

Why are you assuming the OEM parts are inferior just because more power can be made using aftermarket parts? Aftermarket doesn't worry about long term durability, or managing heat from sustained high speed driving, or laws about emissions and noise, etc etc etc.

Maybe I will someday. That new Cayman GTS is so sweet, too bad it probably costs a fortune! Corvette is better than previous versions but still not enough to tempt me to consider getting a US car.

Not talking about OEM vs aftermkt but rather the Z4 getting lousier in-house parts vs certain 1 or 3 series despite costing way more.

Originally Posted by Asbjorn

To be fair, you also didn't get OEM race cats with the 335is. (edit: in fact you didn't with any N54 cars, M or non-M)

Anyway, while the lack of "M" components in is-cars may annoy some, here is why I voted on the 35i with my money

* You get the same DCT transmission as in the previous M3. And it is awesome.
* You get almost the same engine as in an M-car (the 1M), all you have to do is flash the ECU and add an aux water cooler (or just avoid the tracks / going WOT for too long). (to be fair the 1-series M coupe also has an 11% lighter fly-wheel and a larger cooling fan)
* You get the same engine as in an is-car which costs 100.000 rmb / 16.000 usd more here in China, all you have to do is flash the ECU.

Agreed, for me, out of the 3 trims, 35i made the most sense.

Originally Posted by nicknaz

My GUESS is that the decision to go from exhaust outlets on 1 side vs. both sides is a ///Marketing driven one, to show a visual difference between the trims/engine power levels

Oh ya, that's pretty much a given.