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      10-01-2012, 02:30 PM   #23
Hoa
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this is the secondary portion. it doesnt have any sensor. its after the sensors so you wont have any issue
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      11-21-2012, 12:56 AM   #24
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I just deleted the 2nd cats. More burble at downshift not sure about raspy (btw..are raspy and burble similar)..volume about the same...ironically..no more large huge pops..but more a series of smaller gurgles and pops...and as the OP mentioned, more TUM on the upshift.

but i also smell a bit of fumes..and not liking that.

Last edited by AsiaKid; 11-21-2012 at 09:17 AM.
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      12-14-2012, 02:35 AM   #25
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Great mod, but where find the pipes for change the secondary cat?
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      12-14-2012, 04:30 AM   #26
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just take to any auto shop that does engine work of any sort and they should know what to do. they just need to cut it off, find a pipe with same diameter and weld back in
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      12-16-2012, 10:42 AM   #27
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Great mod, but where find the pipes for change the secondary cat?
Go for Milltek. They are direct replacement bolt on. You can easily bolt the old cats back in if you change your mind or sell the car in the future. You wont have to pay the shop to cut and weld again.

The part numbers are: MSBM197 and MSBM198

http://milltekexhaust.pumaspeed.co.uk/

do a search for the part number and add them to the cart. it wont show up as an individual part unless you do that

You will also need the OEM clamps




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      12-16-2012, 12:10 PM   #28
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that is a nice setup
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      12-18-2012, 07:18 AM   #29
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Thank you very muck Hoa, very nice and complete answer!!

Go to miltek shop, quicly.
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      12-19-2012, 05:37 AM   #30
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do you guys think it would sound too raspy even with ar high flow catted downpipe ??
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      12-27-2012, 07:57 PM   #31
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anyone with this mod around Miami? Any shops you would recommend?
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      08-22-2013, 04:31 PM   #32
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Getting ready to do this mod. I bought a full Milltek exhaust for my Z4 a few months ago and it did not fit properly, so I returned it. However, the cat delete pipes fit perfectly and they originally sent me 2 of the same pipe so I still have the right side pipe left over. I am going to buy the left pipe and delete the cats with this setup. I also am running AR DP's that have deleted the primary cats so I will be running a catless exhaust system.

The catless system with the Milltek mufflers was too loud for my taste so I am hoping that it will be perfect with the OEM mufflers.

I am curious as to what you will do when you sell your z4 and put it back to stock. Do you plan on welding the catted pipes back to the stock mufflers, use a band clamp or something else.
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      10-04-2013, 08:12 AM   #33
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Guys, I'm really interested in this mod. Have you experienced any issues with exhaust fumes when the top is open. Some people say they can smell the exhaust a lot....
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      10-05-2013, 07:23 PM   #34
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I haven't gotten brave enough to cut my exhaust in half yet. I have the milltek cat delete pipes sitting in my garage. I can tell you from my previous exhaust that you will have a lot more exhaust fumes. The secondary cats do catch a lot of fumes and carbon.
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      11-03-2013, 11:47 PM   #35
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Quote:
Originally Posted by Hoa View Post
Go for Milltek. They are direct replacement bolt on. You can easily bolt the old cats back in if you change your mind or sell the car in the future. You wont have to pay the shop to cut and weld again.

The part numbers are: MSBM197 and MSBM198

http://milltekexhaust.pumaspeed.co.uk/

do a search for the part number and add them to the cart. it wont show up as an individual part unless you do that

You will also need the OEM clamps
I am doing this mod right now, literally waiting at the 4S shop as I write this. Thanks for posting the part numbers as it made it a lot easier to communicate with the locals. FYI the full 35i miltek exhaust is 22000 CNY here in China. But I am just installing the midpipes.

As you can imagine I am very excited and cant wait to listen to the results.

One of the main reasons I am doing this now is because I just passed my last emissions test. It has however turned out to be much more costly than expected. Those OEM clamps alone were 500 CNY each.

Anyway, I am going with this option as yearly emissions testing becomes a reality starting from 2015. This is because my car is from 2009 and this is Chinese law. With the miltek decatted midpipes it should be very easy to switch back and forth as needed.
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      11-04-2013, 05:16 AM   #36
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Before and after pics attached. We found that miltek had forgotten to ship the small clamp that replaces the oem clamp because the pipes are larger. Also the "professionals" cut the OEM pipes at the wrong place at first and had to weld things back together again. So learn this: The OEM and milktek pipes are of the same diameter where the ends are to meet. You cannot slide one inside the other.........

Anyhow, everything is fine now, and first impressions are that at idle, or while cruising in D/normal and barely touching the throttle, the car is almost as quiet as before. So if you worry that this mod will take away too much comfort for long distance traveling etc, I do not think you have to.

The car is however significantly louder when you start pushing it, and all the pops and "burbles" are much easier to hear now as well. It seems I can now also better control when people turn their heads - my right foot is very delighted.

Update: Cold starts in my basement parking lot sound like small explosions now - it makes the car seem very masculine indeed! Also I am constantly finding myself speeding just to listen to that nice sound. Even with the top up, the sound is very addicting. I like it very much.
Attached Images
  

Last edited by Asbjorn; 11-06-2013 at 01:14 AM.
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      11-12-2013, 11:34 PM   #37
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And here is a video I made today. Not really a one-to-one comparison, but a video none-the-less...

http://v.youku.com/v_show/id_XNjM0MTU0OTUy.html
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      11-13-2013, 02:45 PM   #38
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Quote:
Originally Posted by Asbjorn View Post
BThe OEM and milktek pipes are of the same diameter
Other than switching the downpipe, do you think there are power gains from the exhaust?

Or to ask it another way, if someone wanted the "stage 2" power with OEM sound, this is possible by changing the downpipe and keeping the OEM cat back exhaust, or are there bottlenecks in the airflow with the OEM exhaust?
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      11-13-2013, 06:21 PM   #39
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Quote:
Originally Posted by nicknaz View Post
Other than switching the downpipe, do you think there are power gains from the exhaust?

Or to ask it another way, if someone wanted the "stage 2" power with OEM sound, this is possible by changing the downpipe and keeping the OEM cat back exhaust, or are there bottlenecks in the airflow with the OEM exhaust?
Cobb Stage 2 OTS Tune does not require a cat back exhaust mod. it will work with DP, FMIC, DCI as only mods.

with the exception of 135i. they tested to see that 135i's stock exhaust was too restricting.

My thought is that Cat backs are mostly for sounds, with minimal performance gains.
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      11-13-2013, 09:12 PM   #40
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If anyone is interested I have this mod and never installed it. So, I have brand new and never installed left and right Milltek cat delete pipes.
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      11-14-2013, 02:15 AM   #41
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Quote:
Originally Posted by nicknaz View Post
Other than switching the downpipe, do you think there are power gains from the exhaust?

Or to ask it another way, if someone wanted the "stage 2" power with OEM sound, this is possible by changing the downpipe and keeping the OEM cat back exhaust, or are there bottlenecks in the airflow with the OEM exhaust?
I do not have any experience with switching downpipes. What I did was simply replacing the secondary cats by installing Miltek decatted mid pipes.

Like OP I did this mod only to get better sound. Nothing else. I am not aiming for more power or faster turbo spool up. I just want my turbos to last as long as they would on a normal 35is. Anyway, removing the cats has had a much bigger impact on the sound than any ECU mods I have done. I don't think one can replace the other.

As for power gains, here is how I think it works: The ECU is programmed to target at certain boost psi, which, unless you change something very significant, translates more or less directly into a certain amount of available torque and power. If you get more or less power than what was intended by the ECU, it is because the ECU is not doing its job well enough. You can change the targets with software like ESS or by fooling the OEM software with piggies, but that we all know. This is of course different from what we see in NA engines, where the engine depends on the outside air, and hence looses hp with altitude, "bad" weather or poorly designed intakes as it cannot control it with turbos. Also, as the N54 is forced induction, I don't think it cares much about the exhaust as long as it can reach its psi targets with whatever lag the system has. Opening up the exhaust, especially near the turbos, would reduce lag, but "hopefully" not increase power, as the ECU should control this. And even with the OEM exhaust the turbos have no problem reaching even very high psi levels. So it is not restrictive in this regard. Other things give up much sooner than those. Such as the fueling system for example (like the low pressure pump).

So I should think that even if you removed the downpipes, the ECU should control the turbos enough that you do not see any significant power gains. Any such power gains would have been a result of "unwanted" spikes in boost psi, as the turbos spool up faster than "predicted" by the ECU, and hence get a little out of "control". I wouldn't know if I am right that this could happen, so any engineers are welcome to correct me if I am wrong.

I think installing a better intercooler is a much better way to get the same, or slightly more power, as the ECU realizes it can put less work on the turbos and still reach the targets it is programmed to reach. What is not to like about less pressure drop (flow resistance) AND colder intake air at the same time. The M4 is an even better example of how it should be done.

Back to your original question. I know that other people disagree with me, but I still think that the ESS ecu mod does not increase the sound volume of the exhaust overall. The nature of the sound is different, but that is a different discussion.

But as for volume, I think ESS makes the car slightly more muted in everyday driving, probably because the engine has more torque down low, and can "relax" more. A relaxed engine is a less noisy engine. As for WOT, probably ESS is slightly louder, but where I drive, it is hard to tell the difference.

Overall removing the cats has a much bigger impact on the sound volume than an ECU tune if you ask me. Ie I feel certain that if I went back to the OEM software, I would still have a much greater sounding car than I ever had with our without ESS before installing the miltek decatted midpipes. Hope this makes sense.

Now the next question is what the nature of the sound is with decatted mids vs decatted downpipes vs muffler delete (all 4 cats still installed). Some say that the sound is deeper with decatted downpipes, but it is probably hard to find someone who has tried all three options on the same car. And the mufflers on a Z4 are not the same as on a 1 or 3-series. But I can honestly say that I personally do not want my car any louder than it is now.
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      11-14-2013, 07:49 AM   #42
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Quote:
Originally Posted by Hoa View Post
Go for Milltek. They are direct replacement bolt on. You can easily bolt the old cats back in if you change your mind or sell the car in the future. You wont have to pay the shop to cut and weld again.

The part numbers are: MSBM197 and MSBM198

http://milltekexhaust.pumaspeed.co.uk/

do a search for the part number and add them to the cart. it wont show up as an individual part unless you do that

You will also need the OEM clamps




These are simple bolt on piece? I am considering this along with the 35is exhaust with gold tee.

Any videos of the sound?
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      11-14-2013, 10:16 AM   #43
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Quote:
Originally Posted by VailM3 View Post
These are simple bolt on piece? I am considering this along with the 35is exhaust with gold tee.

Any videos of the sound?
you do have to cut where the clamp is. it is pretty simple. when you want to return back to stock, the same clamp will be able to clamp down the secondary cat
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      11-14-2013, 05:29 PM   #44
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Quote:
Originally Posted by VailM3 View Post
These are simple bolt on piece? I am considering this along with the 35is exhaust with gold tee.

Any videos of the sound?
I have these cat delete pipes for sale if you are interested.
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