BMW-style Backbox Mod - first in UK

[nc_]

So, inspired by what seems a common mod in the BMW community, I’ve had the backbox modified on my car. I should say this is probably less relevant to US owners, but I chose this mod because I didn’t want the added hassle associated with removal of the cat or OPF/GPF.

We opened the back box, gutted the fibre wadding in there, and replaced the perforated tubing connected to the valved exit with solid pipe, and welded the box back up again.
To me this is how the car should have sounded from the factory. Normal mode has a bit more volume and is more tuneful, while Sport mode brings on a real howl. 40 mile drive home from the garage shows no drone, or negative “day to day” effects of doing this. Pretty good value for the difference made for the price, and a good alternative to a full system requiring a map to account for removing the OPF.
£400 all in for a day’s work felt decent going when a full system seems to push a grand! For those with experience of these vehicles, I would say it’s louder than a 718 Cayman with PSE, quieter than an i30 N in N Mode, and no drone at all

Also, Bimmerlink doesn’t work for the Supra, BimmerCode does, but Link doesn’t - I was going to use this to have manual control of the valve but have just opened it and disconnected it in the open position.

There’s a member local to me on here, so we’ll try and meet up to get a video comparing the stock and the modded.

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[KillxPoint]

Curious what the US models look like inside our mufers

 

[SupraCal]

That is great news. I am thinking of doing the same.
Would you have more pictures? I will be asking my mechanic to replicate it.
Any pictures of the inside of the muffler before you gutted it?

 

[nc_]

That is great news. I am thinking of doing the same.
Would you have more pictures? I will be asking my mechanic to replicate it.
Any pictures of the inside of the muffler before you gutted it?

yup, see below!

 

[whoop_ass]

Great info and thanks for posting.
problem is the EU/USDM cars valves work differently, but i am sure you knew that.
it's always open and only closes on cold start.
Sad that the OPF cars are the Quietest by a huge margin :-(

also this is coded in your calibration file on ECU so you cant change it.
look forward to your comparison on stock and your modded box.

 

[nc_]

For those asking, a video of the sound from the guys who did the work: https://www.instagram.com/p/CGUvA0-J_8O/?igshid=7dp6ixtz4vse

 

[2Cool]

Follow up on this one. The US market muffler is different inside. Looks to have a lot more wadding, and a lot less holes. Letting paint dry on it right now, and no pics of my welds cause I am a much better grinder than a welder.

I did cover the few holes that are on the sport outlet side with a 2.75" stainless exhaust strap clamp. Bolted up nice and tight, will last as long as the muffler does.

I don't really think this mod will be worth the effort for US cars. We'll see.

 

[nc_]

Follow up on this one. The US market muffler is different inside. Looks to have a lot more wadding, and a lot less holes. Letting paint dry on it right now, and no pics of my welds cause I am a much better grinder than a welder.

I did cover the few holes that are on the sport outlet side with a 2.75" stainless exhaust strap clamp. Bolted up nice and tight, will last as long as the muffler does.

I don't really think this mod will be worth the effort for US cars. We'll see.

Looks completely different on the inside for you guys over the pond! Very interested to see how it changes the sound on US-spec cars without the OPF/PPF.

I still find the comments on the OPF/PPF making exhausts quiet rather funny, we also have an i30 N with the filters, and it sounds fantastic with the stock system.

 

[2Cool]

It is a bit louder in Sport mode, bit more bass. I'd say that is more due to removing the wadding rather than covering the few holes. I didn't split the entire muffler as I wanted to keep normal mode quiet for highway use, plus my welding skills made this a one hour job just for this small section.

 

[Phil3]

@nc_

a good few months on, how you finding the exhaust now? Do you still drive it with the valve open and disconnected? would you want more noise, or is it just about right?

I’m hoping to take delivery of my car in a couple of months and already been in touch with the same garage you went too about the work

cheers

 

[nc_]

Still bang on the money for me. Haven’t thought about the valve or any other changes at all. Go for it!

@nc_

a good few months on, how you finding the exhaust now? Do you still drive it with the valve open and disconnected? would you want more noise, or is it just about right?

I’m hoping to take delivery of my car in a couple of months and already been in touch with the same garage you went too about the work

cheers

 

[Phil3]

Still bang on the money for me. Haven’t thought about the valve or any other changes at all. Go for it!

nice one, cheers mate...

...also, sorry to say, but there’ll be another yellow Supra about soon too when mine arrives haha Ive seen yours about occasionally in West Cumbria lately! Or at least I think it’s yours haha

 

[nc_]

nice one, cheers mate...

...also, sorry to say, but there’ll be another yellow Supra about soon too when mine arrives haha Ive seen yours about occasionally in West Cumbria lately! Or at least I think it’s yours haha

No worries!
It probably was mine, I think I have the only yellow one until yours arrives. There’s a couple of black ones, white, and that’s it so far.

One thing I would strongly suggest to do is to get it aligned immediately, mine was waaaaay out of any decent alignment. M&B’s alignment system isn’t working at the moment so I had it done at HiQ in Egremont with 1 mm tow in on the front, 1.5 mm on the rear - the camber isn’t adjustable much - but it absolutely transformed the handling,

 

[Phil3]

No worries!
It probably was mine, I think I have the only yellow one until yours arrives. There’s a couple of black ones, white, and that’s it so far.

One thing I would strongly suggest to do is to get it aligned immediately, mine was waaaaay out of any decent alignment. M&B’s alignment system isn’t working at the moment so I had it done at HiQ in Egremont with 1 mm tow in on the front, 1.5 mm on the rear - the camber isn’t adjustable much - but it absolutely transformed the handling,

Yea starting to see an odd few about now, theres a silver one I’ve seen recently too... saying that, it’s still not as if it’s a common car anyway haha

Ahh that’s good to know, I’m debating whether to get it lowered early on so would have got it aligned after that... but even if I don’t lower it I’ll look into that mate cheers

 

[Mark-in-Stoke]

Still bang on the money for me. Haven’t thought about the valve or any other changes at all. Go for it!

Hi mate, the video you linked was that in sport and is there even a difference between sport and comfort modes?
I was under the impression the valve opens in sport but that doesn't appear to be the case with ours?

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