Back box modification - With pics.

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Ducklakeview

Lifer
Ok, after much searching and looking at the options, I reckon I have 3 options;

1: Chop out the box and go for straight pipes - But worried it may be too noisy, AND possible drone.
2: Bypass pipes - But I'd want to go for the 1" ones, and looking at my box, I don't think they would fit, especially with my Monkey Tips.
3: Cutting open the box and modding it, similar to Yorkie's thread here; http://www.z4-forum.com/forum/viewtopic.php?f=2&t=62691&hilit=back+box+mod

So, as I want to keep the car on the road, on the off chance that we get some good weather :D I've just bagged this on Ebay for £30

backbox.JPG

I intend to mod it like Yorkie did, cutting it open and joining the in and output tubes, leaving a small amount of perforated tube for sound reduction, and then packing the wadding back in. This way, I can always revert to STD, or make more mods to the box, as I've had some decent sleeves delivered to the shop today, not bad @ £6.49 ea from Euro Car Parts.

20160708_194616.jpg

So, quick question, does anyone know what stainless the box is made from? I'm assuming it is stainless, although I haven't checked.

Will pop up a post/pics as I'm doing it, and a before/after video.


Mike
 
This is what I did to mine. Just for info. Last page of post has pics of modded backbox.
http://www.z4-forum.com/forum/viewtopic.php?f=2&t=79494&start=165.
 
Ducklakeview said:
So, quick question, does anyone know what stainless the box is made from? I'm assuming it is stainless, although I haven't checked.
Click to expand...

My guess is something like 304 like most stainless things bent or pressed. Fairly standard.
 
GuidoK said:
Ducklakeview said:
So, quick question, does anyone know what stainless the box is made from? I'm assuming it is stainless, although I haven't checked.
Click to expand...

My guess is something like 304 like most stainless things bent or pressed. Fairly standard.
Click to expand...

Cheers. Just had a nice 20L bottle of 95% argo dropped off FOC by a customer, so just waiting for the box now.

Mike
 
Ok, spotted some info on another post about a guy that offers mobile modding to M3 owners, a bit of a Google turns up this little lot;


Apparently this is some of his work;

https://www.facebook.com/Paulscarwelding/

Now this I LIKE the sound of :)

https://www.facebook.com/john.hyde.92754397/videos/10153506967986090/

[youtube]IV2WZc5z7Dc[/youtube]

And I found this how to, which whilst I appreciate my 3.0 won't sound this good, I think this is the way I'm going to go, joining the pipes as per Yorkie's thread, and covering the perforations with tape and exhaust wrap..

[youtube]2C-ECk8Y32I[/youtube]

Mike
 
So, the used box has arrived :)

Looks like my thoughts re 1" bypass pipes were right, not enough room to fit them without making the back ends of the tips visible...

20160712_093445.jpg

I thought this may have been an aftermarket box, but it's original BMW, having been "modded" to slide on and off with welded sleeves, apparently the seller had received it with the car and left the "performance" box on it when he got rid. One less job for me to do then!

20160712_093457.jpg

Have now got exhaust wrap tape, aluminium tape, stainless ties, 50mm sleeves and 2 * 300mm lengths of 50mm stainless tube. The weekend should be fun, and hopefully noisy! Cost so far, around £50 all in, the stainless welding gas and wire were freebies, the box was £30 of that total.

Will take some pics as I do it, and a before/after video/sound clip..

Mike
 
It is most likely 304 any stainless wire will weld on to it it dose not ,matter when welding really. Well not on something like this.
Get yourself a pack of 1mm cutting wheels for you angle grinder. You dont want to be trying to fill a 3mm gap. The stainless is thin and you will start blowing holes. Sorry if i am teaching you to suck eggs. Its just what i have noticed from modding a few M back boxes.
 
Machine monkey said:
It is most likely 304 any stainless wire will weld on to it it dose not ,matter when welding really. Well not on something like this.
Get yourself a pack of 1mm cutting wheels for you angle grinder. You dont want to be trying to fill a 3mm gap. The stainless is thin and you will start blowing holes. Sorry if i am teaching you to suck eggs. Its just what i have noticed from modding a few M back boxes.
Click to expand...

Mat, gone for 308LSi wire with 95% Argon 5% Oxygen. Although I'm a dab hand with the Mig, I've never welded stainless before, but I'm sure I'll get by ;) Already stocked up on 1mm discs ;)

Mike
 
FWIW the M3 oem exhaust mod is ... a drastic change. Videos do not convey how loud it becomes (a friend just did his, and has swapped back to OEM verrry quickly). It was ASBO loud - couldnt drive it at night.
 
jimmybell said:
FWIW the M3 oem exhaust mod is ... a drastic change. Videos do not convey how loud it becomes (a friend just did his, and has swapped back to OEM verrry quickly). It was ASBO loud - couldnt drive it at night.
Click to expand...

Obviously the M3 OEM exhaust is a fair bit louder than the std one on my 3.0 to start with. I'm (probably) going to join the in & out pipes with 50mm stainless tube, and still either utilise the small slotted sections, or more likely cut similar slots into the joining pipes with a 1mm disc. I'll also be replacing the "wadding" before reassembly.

As you can see in this pic pinched from Yorkie's thread, the std box is made differently than the M3, with no actual pipes running between the inlets and outlets, as they are cut allowing the gasses into the "void" which I assume does a lot of the silencing work. My mod will (hopefully) allow more noise out of the back, but prevent boominess. That's the hope anyway :)

Std box;
box std cut open.jpg



Whereas the M3 box has actual pipes linking the inlets & outlets across the box, with perforated sections to allow the stuffing to do it's work;
m3 back box std.jpg



If my mod sounds as loud as a stock M3, or maybe just a "bit" fruitier, I'll be happy :)

Mike
 
Ducklakeview said:
Machine monkey said:
It is most likely 304 any stainless wire will weld on to it it dose not ,matter when welding really. Well not on something like this.
Get yourself a pack of 1mm cutting wheels for you angle grinder. You dont want to be trying to fill a 3mm gap. The stainless is thin and you will start blowing holes. Sorry if i am teaching you to suck eggs. Its just what i have noticed from modding a few M back boxes.
Click to expand...

Mat, gone for 308LSi wire with 95% Argon 5% Oxygen. Although I'm a dab hand with the Mig, I've never welded stainless before, but I'm sure I'll get by ;) Already stocked up on 1mm discs ;)

Mike
Click to expand...

I mostly tig weld i am not so good with mig. But i assume its the same as steel. Stainless and steel mig weld exactly the same.
So you should be a ok buddy all the best :thumbsup:
 
I've gutted lots of OEM silencers for the Z3 MC and the Z4MC (thread posted on here in 2012) and the golden rule that I have discovered is that there must not be a direct line of sight of the inlet pipe into the silencer through the outlet pipe, The exhaust needs take a 90degree turn out of the inlet pipe and then take another 90 degree turn into the outlet pipe: this permits the sound waves to get reflected in the silencer but doesn't impede the gas flow unduly. :thumbsup:
 
You can also make a loop system (which obviously also has turns) where the loop is reintroduced in the same chamber. That noise will be in antiphase for some frequencies.
Similar to the effect of resonance chamber now in the backbox (spring-mass system/helmholz resonator) but with a continous pipe so flow is less effected. I think both the z4m backbox has this and exhausts like supersprint twinloop etc.

But if you want more noise and more power, stainless headers and high flow cats is the way to go. The biggest flow restriction on the m54 is by far the exhaust manifold.
 
GuidoK said:
You can also make a loop system (which obviously also has turns) where the loop is reintroduced in the same chamber. That noise will be in antiphase for some frequencies.
Similar to the effect of resonance chamber now in the backbox (spring-mass system/helmholz resonator) but with a continous pipe so flow is less effected. I think both the z4m backbox has this and exhausts like supersprint twinloop etc.

But if you want more noise and more power, stainless headers and high flow cats is the way to go. The biggest flow restriction on the m54 is by far the exhaust manifold.
Click to expand...

Not really after more power, although that would be nice :) Just a nicer noise!

Mike
 
Ok, so made a start on this last night...

First up, let's get it open..

I chose to go right around the box, about 70mm up from the middle, in order to give me the best access to the internals.

20160714_210909.jpg

20160714_210912.jpg20160714_210916.jpg20160714_210918.jpg

Used my grinder with a 1mm cutting disc.

For some reason it'll only allow 4 pics to be attached, so continued below..

Mike
 
Then in order to release the welds on top, marked with pen, I initially was going to grind them, but that was taking ages, so cut around them instead.

20160714_211410.jpg
20160714_212521.jpg
20160714_214135.jpg

A bit more messy, but nothing I can't re-weld.

Continued below...


Mike
 
And, off with the lid...

20160714_214322.jpg

Then remove the "hair" which I'll be re-installing, so the Wife will have to do without her extensions...

20160714_215600.jpg


Another view;

20160714_215603.jpg

My plan is, to link the corresponding inlet and outlet pipes using 50 or 60mm stainless tube, which I'll be cutting and welding to obtain the required bends. I am also going to cut in some small slots with the 1mm disc, so that they are in the centre section, roughly where they are now. I will then refit all of the "hair" to prevent it being too loud. Hopefully this will give me the best bits of a back box delete, whilst not being too loud..

Will be starting it tomorrow, as I've just picked up my Ebay bargain of the week...

20160714_204611.jpg

A Milwaulkee 355mm cut off saw, used ONCE and they guy was "afraid" of it! Cost him £220 last year, came with 5 discs, manual, receipt and 2yr warranty - all for the princely sum of £60 :oops:

So the cost of this job so far has risen to £110, still cheap I think...

Mike
 
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