Back-box removal trial

HazArc

HazArc

Member
 S Wales / West Oxfordshire
I have my E85 3.0si booked in for some back-box action a week today. The car has a Z4M rear bumper and quad fitted (see picture), but as a weekend car, I want it louder!
I’ve been undecided whether or not to have a full back box delete and I’ve been watching so many YouTube videos, but it ain’t the same!… So my local exhaust specialist is going to cut off the back-box and let me have a drive around the ‘car park’ to get a feel for the sound. If I feel it’s too loud he’s also ordered a custom back-box to install which will be louder than the original but not as much as a back-box delete.

Anyone else opted for an aftermarket back-box over a full delete? I’ve seen some have had their original bock-boxes modified.
 

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I did a backbox delete on my first Z4 2.5si and loved it, but I was younger back then.

In my second Z4, a 3.0si coupe I opted to have the backbox internal gubbins altered very slightly and found that was the best of both worlds.
 
I did a backbox removal and decided to switch to louder muffler.
However now I have decided to totally change my exhaust.
The drone, between 2k and 3k rpm in unbearable. And this is the typical cruising rpm and it's impossible to have a normal conversation :)

There are two pipes coming from the headers. I consider adding a Y splitter after the cats, single center muffler and a single pipe to the backbox.
 
Do this back box mod...https://z4-forum.com/forum/viewtopic.php?p=2105158#p2105158
I've done this and it pretty much perfect, a really nice noise when your driving like a spanner but pretty much normal when your not. There is a little drone @3k but just having the radio on at a volume where you can talk to your passenger and that will hide it.

I will be de-catting it after the MOT, so that will be even better.
 
Thank for the info and opinions. Taking on board what you’ve all said, I reckon I’ll probably opt to have the custom back box fitted instead of a full delete. The exhaust needs work anyway as the additional twin pipe that was added to make the quad exhaust has internal issues.

Thinking the full delete will be too loud and produce too many bangs and pops….
 
The pops and bangs on a stock program and stock kats aren't that noticeable. It's just a hint of pops.
And I'm coming from M2 with M Performance exhaust.

Well you can always ask the garage to make a cut in the exhaust, drive around the block and see how you like it :) Think outside the box ;)
 
detch said:
The pops and bangs on a stock program and stock kats aren't that noticeable. It's just a hint of pops.
And I'm coming from M2 with M Performance exhaust.

Well you can always ask the garage to make a cut in the exhaust, drive around the block and see how you like it :) Think outside the box ;)
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That’s exactly what I said is going to happen. The back box is coming off whatever happens. So I’m going to drive it around with it off to begin with to see what I think of it before I make a decision. Although I’ll need to make the decision there and then…
 
I have a 3.0si too. I fitted a custom rear box and done a center box delete with a AFE stage 2 cold intake. Sounds very nice and isn't too loud.
 
I've hear an Si with a back-box delete and it's way louder than I would want to travel more than a few miles!

But then the owner had it converted to quad pipes and it sounded much more bearable.
 
Mr Tidy said:
I've hear an Si with a back-box delete and it's way louder than I would want to travel more than a few miles!

But then the owner had it converted to quad pipes and it sounded much more bearable.
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Pretty much what I was going to do. But like you’ve just confirmed, I’m concerned it may be too loud. Especially as I’m going to be doing some motorway driving from time to time (Oxford to Wales).
I’m still going to test it without the backbox, but pretty sure I’m going to opt for the aftermarket backbox to be fitted.
 
HazArc said:
Pretty much what I was going to do. But like you’ve just confirmed, I’m concerned it may be too loud. Especially as I’m going to be doing some motorway driving from time to time (Oxford to Wales).
I’m still going to test it without the backbox, but pretty sure I’m going to opt for the aftermarket backbox to be fitted.
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Definitely worth trying it with no back box, but I don't think you'll enjoy it. When the back box started blowing on my V8 Rover I took it off and drove around the block - it sounded fantastic, but being only 21 at the time I just knew I'd be getting stopped by the BIB pretty frequently. :roll:

It's about finding the right balance. What can be great on a B Road thrash may be tiring on a long Motorway trip or seem a bit ASBO going to the shops!

My second 3.0Si came with a custom cat-back system already fitted and it was great. A bit more volume, some pops and bangs but no drone on Motorways.

Good luck finding a set up you like. :thumbsup:
 
Mike6 said:
Watch out for the MOT test, I understand test stations are getting very iffy about modified exhausts
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Yeah this was a concern. Haven’t heard of anyone failing an MOT with a back box delete, but the aftermarket backbox which ‘may’ be fitted is fully compliant…. For now
 
Back Box delete sounds absolutely great .....for about 2 days, then you'll just get p155ed off with the constant drone
 
Number5 said:
Back Box delete sounds absolutely great .....for about 2 days, then you'll just get p155ed off with the constant drone
Click to expand...

Thanks for the advice. This is what I’m worried about 👍
 
HazArc said:
Number5 said:
Back Box delete sounds absolutely great .....for about 2 days, then you'll just get p155ed off with the constant drone
Click to expand...

Thanks for the advice. This is what I’m worried about 👍
Click to expand...

If affordable, go for a switched valve so you have the option at the flick of a switch. I've seen people with a little remote fob that operates it.
 
I had a backbox delete on the 3.0si.

Personally I instantly (and I mean the very second I drove the car after doing it) regretted it, and immediately phoned a garage to book it in to weld the backbox back on. I had to live with it for 2 weeks until they could fit me in, so I had plenty of time and mileage (both fun miles and commuter miles) to dwell on my mistake :lol: .

It was WAYYYYY too loud, and really horridly boomy at 3k under load. It was vaguely entertaining when nailing it but the amount of noise didn't justify the rate of acceleration, so it actually made the car feel a bit flat honestly! One other point is as regards the pops and bangs with the backbox delete; Jesus Christ it was like coming under fire from an anti-aircraft gun when you nailed it and then lifted off at high rpms.

After welding my OE backbox back on, I cut and welded straight pipes in place of the centre silencer. This imo was the perfect middle ground - bit more rasp and bass, not boomy on the motorway or at low rpms under load, but enough extra noise to feel quite sporty.

Horses for courses, and I know I'm getting old, but even back in my mid-20s when I did the backbox chop I felt it was too loud and the sound wasn't particularly nice either.

Do your ears a favour and either get a proper aftermarket backbox on it, or just straigh-pipe the midbox and leave the rest alone :thumbsup:
 
Thanks for that. After all these comments I am leaning towards the aftermarket backbox. I’m still going to drive it around, hopefully up to 60 on the bypass just to sample the drone with the backbox removed, but pretty confident I’m going to get the aftermarket backbox fitted.
 
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