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      07-27-2009, 04:23 PM   #1
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OEM exhaust design...

Now that I have my stock exhaust off the car I could get a closer look at it. Seems to me the bends are 'kinked' bad (no mandrel bending). Also for those who have switched out their exhaust for an aftermarket system, do you think the lack of heat shields(found on the stock unit) that are not on most aftermarket exhausts, have any adverse effect? What were the heat shields shielding?

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      07-27-2009, 04:34 PM   #2
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Quote:
Originally Posted by ///Metak View Post
Now that I have my stock exhaust off the car I could get a closer look at it. Seems to me the bends are 'kinked' bad (no mandrel bending). Also for those who have switched out their exhaust for an aftermarket system, do you think the lack of heat shields(found on the stock unit) that are not on most aftermarket exhausts, have any adverse effect? What were the heat shields shielding?

Attachment 290395
That helps block radiated exhaust heat from rasing the temperature of the diff. (and the gear oil inside the casing)
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      07-27-2009, 04:38 PM   #3
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Quote:
Originally Posted by ///Metak View Post
Now that I have my stock exhaust off the car I could get a closer look at it. Seems to me the bends are 'kinked' bad (no mandrel bending). Also for those who have switched out their exhaust for an aftermarket system, do you think the lack of heat shields(found on the stock unit) that are not on most aftermarket exhausts, have any adverse effect? What were the heat shields shielding?

Attachment 290395
Yes, the OE exhaust system is not mandral bent pipe, and that does ultimately effect the flow and back pressure.
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      07-27-2009, 04:47 PM   #4
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Quote:
Originally Posted by Lemans_Blue_M View Post
That helps block radiated exhaust heat from rasing the temperature of the diff. (and the gear oil inside the casing)
I figured it was for the diff. because it right by those particular bends, but how much of an issue is heat going to be with the aftermarket systems? I'm not losing sleep or anything, just curious.

What I find strange is the 1st, 2nd and 4th bends seem almost as if they were mandrel bent(a lot smoother), but that 3rd bend is bad, almost as if it were by design, dunno?
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      07-27-2009, 05:04 PM   #5
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I am not sure how the pipe is bent, but it is triangular in places so that it fits better through the curves. It is really weird, but I am sure BMW did it that way on purpose.

-Andy
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      07-27-2009, 05:05 PM   #6
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The heat shields are placed near the CV boots on the E92 M3.

We've found that not running heat shields will result in premature wear of the CV boots, and will cause CV failure in some situations involving especially hard driving. We install heat shields on all Eisenmann connecting pipes for that reason.
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      07-27-2009, 05:09 PM   #7
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Quote:
Originally Posted by Ilia@IND View Post
The heat shields are placed near the CV boots on the E92 M3.

We've found that not running heat shields will result in premature wear of the CV boots, and will cause CV failure in some situations involving especially hard driving. We install heat shields on all Eisenmann connecting pipes for that reason.
Hmmm, I might have a muffler shop do that for me on my Dinan system. Thanks!
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      07-27-2009, 05:15 PM   #8
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Quote:
Originally Posted by ///Metak View Post
I figured it was for the diff. because it right by those particular bends, but how much of an issue is heat going to be with the aftermarket systems? I'm not losing sleep or anything, just curious.
OE exhaust applications typically go overboard on such things like heat shielding to avoid unintended consequences. (even if the chances of any real impact are remote)

The engineering group at Arvin Meritor, (M3 OE exhaust supplier) probably suggested this to BMW during their R&D.

This precaution was implemented due to the close proximity of the dual exhaust pipes as they 'snake' around the differential casing.

I can't see that it would make much difference, but I guess it wouldn't hurt to re-use them. (or fabricate something similar)

I would only do this if you are truly concerned about the additional heat transfer from your unshielded aftermarket exhaust.

No idea how much difference it really makes...
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      07-27-2009, 05:25 PM   #9
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Quote:
Originally Posted by Lemans_Blue_M View Post
OE exhaust applications typically go overboard on such things like heat shielding to avoid unintended consequences. (even if the chances of any real impact are remote)

The engineering group at Arvin Meritor, (M3 OE exhaust supplier) probably suggested this to BMW during their R&D.

This precaution was implemented due to the close proximity of the dual exhaust pipes as they 'snake' around the differential casing.

I can't see that it would make much difference, but I guess it wouldn't hurt to re-use them. (or fabricate something similar)

I would only do this if you are truly concerned about the additional heat transfer from your unshielded aftermarket exhaust.

No idea how much difference it really makes...
I think the diff. would withstand heat better than the rubber parts of the CV like Ilia@IND suggested. Worth looking into IMO.
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      07-27-2009, 05:39 PM   #10
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Quote:
Originally Posted by ///Metak View Post
I think the diff. would withstand heat better than the rubber parts of the CV like Ilia@IND suggested. Worth looking into IMO.
Yes, CV joints would certainly be more susceptible to the heat.

That's one of those unintended consequences I suppose.

Hmm...

I wonder how many other exhaust manufacturers, retailers, and install shops have figured this out...
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      07-27-2009, 05:40 PM   #11
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I have seen the rubber boots melt because of the heat, and lose all of the grease packed into the CV joints, but this happened with a very large diameter race exhaust, during an endurance racing event.
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      07-27-2009, 05:50 PM   #12
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Quote:
Originally Posted by Ilia@IND View Post
I have seen the rubber boots melt because of the heat, and lose all of the grease packed into the CV joints, but this happened with a very large diameter race exhaust, during an endurance racing event.
Question...

Did IND figure this out over time...or did Eisenmann alert you to this before you sold their product?

Curious to see who discovered this issue, and when was it identified as a potential problem.
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      07-27-2009, 05:55 PM   #13
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Quote:
Originally Posted by Lemans_Blue_M View Post
Question...

Did IND figure this out over time...or did Eisenmann alert you to this before you sold their product?

Curious to see who discovered this issue, and when was it identified as a potential problem.
I'm sure that's classified info lol...
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      07-27-2009, 05:58 PM   #14
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Quote:
Originally Posted by PunjabiM3 View Post
I'm sure that's classified info lol...
It's a fair question to ask a reputable vendor on this site.

Besides, I know classified...and that type of thing ain't classified brother.
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      07-27-2009, 06:09 PM   #15
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I know people are selling their OEM units and fetching $150-200 and that's for an uncut system! I just can't sell it for such a small amount of money, I may need it again someday, who knows. So for now it will be 'wall art' in my man cave(garage)!

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      07-27-2009, 06:19 PM   #16
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I would bet the tubing is hydroformed, this process uses very high fluid pressure along with a "mold" for the outside shape desired. The tubing is very purposefully shaped into a non round cross section in certain sections. My guess (without looking under my car recently) is that it is for clearance - either to other parts of the chassis or to the ground.

On another note we debated the need for exhaust shields quite a bit on this thread. My conclusion was just what IND is saying above. A user installed heat sheild sounds like a darn good way to play it plenty safe with any aftermarket exhaust system. Link to that thread here.
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      07-27-2009, 07:34 PM   #17
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As I stated in the other thread, I really don't think the shields are there to block the radiation into the diff because the amount of heat generated and transferred by the diff is much more than the amount of heat transferred via radiation through that small patch of the exhaust pipe. Plus, the diff gets pretty hot to begin with, so the delta_t between the diff and the exhaust pipe would be somewhat low.

Ilia@IND, how do you know the CV joints melted because of the heat radiated from that part of the exhaust as opposed to the heat conducted by the diff? Did the problem go away after you installed shielding? And on what type of car was the failure you described happen? Finally, do you have any sense of how hot exactly that part of the exhaust gets during hard driving? The answer to that question would inform the discussion we were having in the other thread. Thanks.
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      07-27-2009, 07:43 PM   #18
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Quote:
Originally Posted by swamp2 View Post
I would bet the tubing is hydroformed, this process uses very high fluid pressure along with a "mold" for the outside shape desired. The tubing is very purposefully shaped into a non round cross section in certain sections. My guess (without looking under my car recently) is that it is for clearance - either to other parts of the chassis or to the ground.

On another note we debated the need for exhaust shields quite a bit on this thread. My conclusion was just what IND is saying above. A user installed heat sheild sounds like a darn good way to play it plenty safe with any aftermarket exhaust system. Link to that thread here.

Thanks, I must have missed that thread. I am probably going to play it safe and get some sort of shield on my exhaust.
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      07-27-2009, 08:52 PM   #19
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Quote:
Originally Posted by swamp2 View Post
I would bet the tubing is hydroformed, this process uses very high fluid pressure along with a "mold" for the outside shape desired. The tubing is very purposefully shaped into a non round cross section in certain sections. My guess (without looking under my car recently) is that it is for clearance - either to other parts of the chassis or to the ground.

On another note we debated the need for exhaust shields quite a bit on this thread. My conclusion was just what IND is saying above. A user installed heat shield sounds like a darn good way to play it plenty safe with any aftermarket exhaust system. Link to that thread here.
Yes, the M3's OE exhaust system is manufactured by Arvin Meritor using an internal high-pressure hydroforming molding process.This technology allows them to manipulate the size and shape of the exhaust tubing to fit tight areas, that would normally cause clearance problems.

Without the use of this technology, it would lead to unwanted NHV in the interior cabin.

Arvin Meritor has been the primary OE exhaust supplier for BMW for several years. They were the first exhaust company to make a tubular exhaust manifold using this new hydroforming exhaust molding technology in the early 1990's.

They have a factory located in Spartanburg, South Carolina near the BMW plant.




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      07-27-2009, 11:04 PM   #20
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Honestly, most people won't see a difference. Most people have only had their cars for about one year max, less have aftermarket exhausts, and even less actually track it hard enough to see high temperature in the exhaust. If there are any problems with not having a shield, we probably won't see any reports until a bit later.

But the heat shield only costs like $40, so why not play it safe?

Lucid, if you could take some temp measurements during a track session, let us know.

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      07-28-2009, 02:33 AM   #21
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Quote:
Originally Posted by rldzhao View Post
Lucid, if you could take some temp measurements during a track session, let us know.
I've actually measured the exhaust pipe temp at that exact spot on my aftermarket exhaust right after full-on track sessions at ~180C in the paddock, which seems pretty harmless. I suspect the actual average operating temps during a track session like that are actually much higher given the pipe is thin and cools off rapidly, but I didn't pin it down. I think you are right that if running without a shield significantly impacts the CV joints, it would surface in the long term. I don't currently have any issues with my CV joints (I check them regularly).
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      07-28-2009, 11:26 AM   #22
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Quote:
Originally Posted by lucid View Post
As I stated in the other thread, I really don't think the shields are there to block the radiation into the diff because the amount of heat generated and transferred by the diff is much more than the amount of heat transferred via radiation through that small patch of the exhaust pipe. Plus, the diff gets pretty hot to begin with, so the delta_t between the diff and the exhaust pipe would be somewhat low.

Ilia@IND, how do you know the CV joints melted because of the heat radiated from that part of the exhaust as opposed to the heat conducted by the diff? Did the problem go away after you installed shielding? And on what type of car was the failure you described happen? Finally, do you have any sense of how hot exactly that part of the exhaust gets during hard driving? The answer to that question would inform the discussion we were having in the other thread. Thanks.

When our friends at Fall Line ran an OEM exhaust system, the CV boots did not melt, but after installing their competition exhaust system with no heat shields, they experienced quite a bit of trouble with melted CV boots. Since then, Fall Line has added heat shields to their competition exhaust, and it is this experience that leads me to believe that heat shields are necessary to protect the rubber CV boots.
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