Loud and legal (UK)

Z

Zowen

Member
 Wigan
Hi I have a 2004 registered z4 with the m54b30 engine and was wondering what I can do to make it louder and legal in the uk. I know I can get a sports muffler but am unsure what im looking for as options seem limited. I was thinking of removing back box however im pretty sure that's illegal.

If anyone has reccomendations on what I should do or search for that would be amazing or if theres any good ebay listings or mod shops in the north west of england.
 
How loud do you want?

I've heard a facelift 3 litre with the N52 engine that had a back-box delete and it was LOUD! The owner admitted it droned quite a bit at Motorway speeds too. I've no idea about legality though.

There used to be a forum member in Cheshire who opened up the box and modified it for more volume, but after a couple of transactions went badly wrong (one involved a mail order purchase of a modified box) he got removed from the forum.

If you find someone on Facebook who relocates Z4 roof motors in Newton-le-Willows that's him. But you might want to get it fitted before you pay!
 
Mr Tidy said:
f you find someone on Facebook who relocates Z4 roof motors in Newton-le-Willows that's him
Click to expand...
Now moved to larger premises in nearby Burtonwood...
 
…

Getting back to the topic itself: you could consider a mid-resonator delete. Bastuck build a replacement mid-section at a decent price :thumbsup:
 
I test drove an N52 E85 with the back box deleted and it was loud, and even at low speeds always loud and can imagine quite drony.

I got an E85 now which had the backbox modified, can see where a square was cut out and rewelded, assume the baffles etc. inside it were removed. Is about bang on now, louder than stock, not as loud as the delete, and still gives nice burbles and over run.
 
Bought my 57 reg E86 with a back box delete and custom pipes.
Very droney and sounded more like a blown exhaust to me.
Sourced a back box and replaced the custom pipes.
Pulled some foam from the sound generator pipe...a better option for me.
 
Mine has the centre cat deleted. It burbles and pops now and and again.
It was significantly louder with an AFE air intake but I took it off because I'm too old for all that nonsense!
 
I daily an N52 Z4; only a backbox delete with custom exhaust tips (which make the burbles quite a bit bigger/louder). I don't notice any drone in the drivers seat during highway and city driving. However, there is a lot more drone and the exhaust is much louder in the passenger seat for some reason (it's bearable, and I think I'd get used to it pretty quickly). I've also been pulled over twice and the cops did not cite me for the noise.

Also my car seems to be one of the quietest at car meets (especially next to the Mopars and VQs).

Can't speak on passing tests for car registration in the UK, but my car did pass all tests with the backbox delete in the extremely anti-modified car state of California.
 
Mr Tidy said:
If you find someone on Facebook who relocates Z4 roof motors in Newton-le-Willows that's him. But you might want to get it fitted before you pay!
Click to expand...

The Zed Shed! yes I'm going to him for roof motor and intend to ask him which is good as I live close.

I saw he does a back box delete or swapping it out which would be great.

I do want it pretty loud just not stupidly loud where its too obnoxious but i can still hear the beautiful m54 engine roar.

Luckily I have hearing issues and struggle hearing low and high ranges of frequency so ive never had to experience droning :)
 
Zowen said:
Mr Tidy said:
If you find someone on Facebook who relocates Z4 roof motors in Newton-le-Willows that's him. But you might want to get it fitted before you pay!
Click to expand...

The Zed Shed! yes I'm going to him for roof motor and intend to ask him which is good as I live close.

I saw he does a back box delete or swapping it out which would be great.

I do want it pretty loud just not stupidly loud where its too obnoxious but i can still hear the beautiful m54 engine roar.

Luckily I have hearing issues and struggle hearing low and high ranges of frequency so ive never had to experience droning :)
Click to expand...
Ask Mike to do his secondary cat removal and 'regular' modified back box :thumbsup: This is what I have been running for almost 2 years now. His 'regular' mod'd backbox is plenty loud enough without being obnoxious and doesn't drone on the motorway etc. His secondary cat removal involves opening up the cat cans and removing the ceramic internals which after 20 years will be doing absolutely zero with regards to emissions. They will be in a shocking state (I have photos of mine) and just hinder gas flow. Their removal frees up that gas flow giving noticeably better throttle response and liberates a little more noise when on full throttle and during lift-off over-run. The cans are re-welded on their top sides and when the exhaust is re-hung there is no sign of them having been de-cat'd...so no suspicious MOT testers !
My car has passed 2 MOT's now with this set-up, the latter also with my Infinitas supercharger fitted and I have had no emissions problems at all. It sounds great, plenty loud enough but NEVER obnoxious. If you do want it any louder Mike can alter the backbox internals to give less sound absorption and more noise :D
 
patriot66 said:
Ask Mike to do his secondary cat removal and 'regular' modified back box
Click to expand...

I did ask about the modified black box he said hed get back to me when he has time coz hes so busy and said it was just under 300 for it. Do you remember how much removing second cat is?
Also have you removed one of the foam pieces in the sound generator or have you left them be?

One of the things I love about the Z4 is its such a beautifully sounding engine none of this high pitch screech or farting sound its a nice balance of everything in my opinion
 
patriot66 said:
Ask Mike to do his secondary cat removal and 'regular' modified back box
Click to expand...

I did ask about the modified black box he said hed get back to me when he has time coz hes so busy and said it was just under 300 for it. Do you remember how much removing second cat is?
Also have you removed one of the foam pieces in the sound generator or have you left them be?

One of the things I love about the Z4 is its such a beautifully sounding engine none of this high pitch screech or farting sound its a nice balance of everything in my opinion
 
Zowen said:
patriot66 said:
Ask Mike to do his secondary cat removal and 'regular' modified back box
Click to expand...

I did ask about the modified black box he said hed get back to me when he has time coz hes so busy and said it was just under 300 for it. Do you remember how much removing second cat is?
Also have you removed one of the foam pieces in the sound generator or have you left them be?

One of the things I love about the Z4 is its such a beautifully sounding engine none of this high pitch screech or farting sound its a nice balance of everything in my opinion
Click to expand...
Unfortunately I don't remember exactly how much secondary cats removal was. He fixed a quite serious gearbox electrical fault on my F11 5er Touring followed next day by the Z4 decat...back in December '21 ! Cost me about £700 altogether and I think the decat was something in region of £150-200 but don't quote me :?
With regards the sound generator foams ; my Z4 is a 2.5i M54 which didn't have them fitted and no need to retrofit one now as the supercharger provides a whooshing and whistling soundtrack all of its own up front :D
To be honest in my opinion if you get a decent exhaust set-up/sound then the sound generator is a complete waste of time. Your attention will be 100% on the sonorous roar going on behind you :thumbsup:
 
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