Derestricted Exhaust

[pingu]

I had a spare exhaust system, so I thought I'd have a look inside. The first thing to note is that it's a double-skin exhaust.

Under the double skin was this...

(RH Silencer)

Here's a diagram showing how the exhaust flows...

(RH Silencer)

Main entry pipe is fully open in Chamber 1, perforated in Chamber 2 and sealed from Chamber 3.

Secondary pipes are perforated in Chamber 1, perforated in Chamber 2 and fully open in Chamber 3.

Exit pipes are sealed from Chamber 1, sealed from Chamber 2 and perforated in Chamber 3.

---------------------------

I have de-restricted the exhausts by removing the secondary pipes and removing the perforations on the exit pipes...

(LH Silencer)

Here's a diagram of the new exhaust flow...

(RH Silencer)

The inner cut-out was welded back in place, then sealed with exhaust repair paste. The system was tested to a pressure of 8 bar. The outer cut-out heat shield was attached using exhaust repair paste, then painted using high temperature exhaust paint.

Finished result...

(LH Silencer)

All the modification has been done to the top of the silencer and none of this can be seen from under the car.

I can't objectively tell you what the improvements are, but it does sound slightly "fruitier" and a little bit less of a screamer at mid-revs.

There is less engine braking and the engine seems to rev more freely.

[msassoon]

No wonder they are so heavy! That is seriously restricted, and I am glad mine is gone.

[shantybeater]

Thanks for posting up, very interesting to see its internals

[Dave'z3]

I know bugger all about the mechanics of cars, but that was informative and not boring. Really good right up and photos.


Thanks for sharing,

Dave

[exdos]

I had a spare exhaust system, so I thought I'd have a look inside. The first thing to note is that it's a double-skin exhaust.

That's plagiarism! Your work is NOT original. Methinks you've been copying my postings on the Z3mcoupe website. Funny that I posted similar photos of "how to do" in the days before you started this thread here: http://www.z3mcoupe.com/forum/showthread.php?t=10267

[markrnorton]

I had a spare exhaust system, so I thought I'd have a look inside. The first thing to note is that it's a double-skin exhaust.

That's plagiarism! Your work is NOT original. Methinks you've been copying my postings on the Z3mcoupe website. Funny that I posted similar photos of "how to do" in the days before you started this thread here: http://www.z3mcoupe.com/forum/showthread.php?t=10267

hey , this is a useful post, saying its not original isn't relevant exdos. I did this last year, but didnt post on it. Does this make your post non-original ? no

People have been chopping boxes for years, its not new

[Bill-]

It seems like a coincidence to me. loads of bikers do this kind of thing maybe you both had the same Idea

[exdos]

It seems like a coincidence to me. loads of bikers do this kind of thing maybe you both had the same Idea

So much of a coincidence that Pingu managed to cut open his silencer in the identical way to the photo I posted just 3 days before in the thread I gave above! Note my "wink" in my posting above. In posting my photos and information about exhaust modding, I do it in the spirit of sharing with other ///M owners, so that others can COPY, as Pingu has done, if they wish. I've been posting on this subject for about 7 years and posted loads of information on the Z3MCoupe website showing the gains that air-intake and exhaust modding can do from the ECU datalogging that I've done. I have no problem with anyone copying it. If anyone wants to improve the performance of a Z3M, then do a search on the z3mcoupe forum and they'll find lots of info to help.

[hornel Z3M]

Nice one exodus. give us a few search words coinciding with your tips on improvements...

[exdos]

Try "silencer", "intake" and "Dashdyno" in the search facility and there should be a fair bit to be going on with.

[hornel Z3M]

Cheers Mate

[Mac The Tank]

Calm down children, i'm sure people have been cutting up exhausts since they started to restrict them.


Mac

[pingu]

I had a spare exhaust system, so I thought I'd have a look inside. The first thing to note is that it's a double-skin exhaust.

That's plagiarism! Your work is NOT original. Methinks you've been copying my postings on the Z3mcoupe website. Funny that I posted similar photos of "how to do" in the days before you started this thread here: http://www.z3mcoupe.com/forum/showthread.php?t=10267

Just a few points I'd like to make about the quoted post.

1. I never googled to see if anyone else had done this, but I did search zRoadster and I found nothing.

2. I never imagined for one millisecond that I was the first person to cut open something to see how it works and then try to improve it. It would only be plagarism if I claimed that I was the first to gut-out an exhaust.

3. I've looked at the thread on z3mcoupe and I struggle to understand what you have done other than cut open an exhaust, especially since all the images in your linked thread are just red Xs.

4. The intention of this thread is to show those who are interested what is involved in the task.

5. I doubt if there are any mods that haven't been done before, so does that mean that you will be accusing everyone of plagarism?

BTW, I found this dated from 2008...

http://forums.bimmerforums.com/forum/sh ... ?t=1012663

[edit] My first photo was taken on 02-07-2011 at 13:16

[Badman gee]

why get so animated about an exhaust

[exdos]

Ooooh! I have hit a nerve!

The clue to my sentiments in my first posting was the "wink" , as in "I know where you've got that idea from" - wink, wink, nudge, nudge, say no more! (said in the voice of Eric Idle)

I've been posting about the modding of the silencers on the z3mcoupe forum and on here since 2006, including this thread on this forum as found here: http://www.zroadster.net/forum/viewtopi ... highlight= I know some ZM owners will copy the idea, and for gawd's sake, I post the information to help others do it!

Pingu, you've not actually removed the reverse flow restriction by the way you've modded the internals, the exhaust gases still need to take a reverse flow sinusoidal ("S"-shaped) path through your silencer.

Also, if you can weld the inside stainless skin to reseal the box why have you not also welded the outside skin too? The best way of resealing the silencer is to tack weld the inside skin in just a few spots about 2inches apart, then grind those welds down so that the outside skin will fit flush on top, and then tack weld the outer skin in place so that you don't distort the metal and then finally weld the entire seam. This will ensure that both inside and outside skins get welded together. Exhaust paste just cracks.

[pingu]

Ooooh! I have hit a nerve!

Accusing someone of plagarism IN CAPITALS (with or without a smiley) is close to libelous, so unless you can prove plagarism I would be more careful in future if I were you. Personally, I'm fairly chilled about comments made on t'web as I have inadvertently made the mistake before of thinking a smiley is a strong enough signal that it was only a joke.

I've been posting about the modding of the silencers on the z3mcoupe forum and on here since 2006, including this thread on this forum as found here: http://www.zroadster.net/forum/viewtopi ... highlight= I know some ZM owners will copy the idea, and for gawd's sake, I post the information to help others do it!

When I clicked on your link to the z3coupe site, the page is unavailable. You were asked to post on zRoadster, but chose not to. You instead decided to link to another website that has not maintained the page. This is why I always repost on websites rather than using links that are likely to be broken.

Pingu, you've not actually removed the reverse flow restriction by the way you've modded the internals, the exhaust gases still need to take a reverse flow sinusoidal ("S"-shaped) path through your silencer.

By removing the multitude of perforations and replacing them with larger holes MUST reduce the restriction. Although I have not objectively tested the modification.

The reversal of exhaust flow inside a plenum is a noise suppression tool and is nothing to do with sine waves. I know that the flow reversal is still there and I don't think that I stated that I had removed it.

Sine waves inside an exhaust system are more to do with the resonant effect of tuning the length/diameter of an exhaust to aid gas extraction.

If you know the revs you want peak extraction you can tune the exhaust length and exhaust diameter to suit. I have done neither of these things.

Also, if you can weld the inside stainless skin to reseal the box why have you not also welded the outside skin too? The best way of resealing the silencer is to tack weld the inside skin in just a few spots about 2inches apart, then grind those welds down so that the outside skin will fit flush on top, and then tack weld the outer skin in place so that you don't distort the metal and then finally weld the entire seam. This will ensure that both inside and outside skins get welded together. Exhaust paste just cracks.

I'm pretty sure that the inside of the silencer is mild steel and only the outer skin is stainless (not that this matters too much). I fully welded the inner skin and used exhaust paste to seal it (tested to 8 bar using a compressor and talcum powder as an indicator). The OEM inner skin is fully sealed, so that's what I wanted to do. As there was exhaust paste directly next to the outer skin I decided not to weld it as the paste would probably react to the heat. I agree that the paste will probably crack over time, but I was only seeing what the effect of the mod would be.

When I patent the mod and go into full production with my new Exdoaust Pipe I will do a much better job .

[Z3cade]

will i be the first to do it to a 2.8?

wouldnt mind having ago at this.. but will it give any real gains?
i say this as on some cars (eg subaru impreza) if the air intake and exhaust flow is changed it can acturly lower bhp and torque as the ecu tends to hold back as it detects a change....? and wont give any gains till its been remaped...

or is the bmw system different?

[pingu]

will i be the first to do it to a 2.8?

wouldnt mind having ago at this.. but will it give any real gains?
i say this as on some cars (eg subaru impreza) if the air intake and exhaust flow is changed it can acturly lower bhp and torque as the ecu tends to hold back as it detects a change....? and wont give any gains till its been remaped...

or is the bmw system different?

I'm under the impression that the BMW system maintains the A/F mixture as best it can throughout the rev range. There will be problems when it can't inject enough fuel quickly enough, but there is a long way to go before that happens.

I don't think you will have a problem.

[Z3cade]

only way to find out would be to dyno it before and after i supose....

[Mac The Tank]

My favourite dyno is just below my right ankle...

I'm in the favour that if you get a second back box - you can then compare between gutted and not, and not have to worry about wrecking it too much. If you like the modded can, keep it and sell on the standard one to top up the beer/fuel kitty.

Not that I promote using beer as fuel, but I have been known...


Mac