[JoshU]

I'm looking for anyone with experience in doing this. I've purchased the diffuser but I'm looking at getting the most sound improvement (I know it's still a diesel) without removing DPF/Cat and I want to understand if there's any risks involved in this.

So far I'm leaning towards a backbox delete as it seems to be the most popular option but I'm also considering some kind of catback system or something. Any helpful input is appreciated!

Thanks,
Josh.

[JoshU]

Originally Posted by JoshU

I'm looking for anyone with experience in doing this. I've purchased the diffuser but I'm looking at getting the most sound improvement (I know it's still a diesel) without removing DPF/Cat and I want to understand if there's any risks involved in this.

So far I'm leaning towards a backbox delete as it seems to be the most popular option but I'm also considering some kind of catback system or something. Any helpful input is appreciated!

Thanks,
Josh.

Or does anybody know of anyone that's had the work done and regret it?

[Techno 9000]

I used a Dual back box from a 335i and found if anything that it was quieter.

Possibly not what you want, but even with the back box delete people say it isn’t much noisier and certainly not the character of sound that they would hope for.

[JoshU]

So you were looking to keep the sound the same anyway? I know it isn't going to increase the volume much at all but even a slight increase in volume and depth I'd be happy with.

Have you heard one of these engines with a backbox delete in person? The problem is that I've only heard them in videos and I think they sound fine but it's not going to be ideal if I do it and it sounds terrible in person.

Thanks for the reply

[Techno 9000]

Hi

I wasn't looking for more noise / volume from the change, just the looks(requested by my wife)

I was thinking of whether a bespoke solution for operating the valve in the left hand tailpipe would be required to keep the noise down, but the option to use the valve went out when the tailpipe needed a greater length taken off to manufacture the bend to the new position. No problem in the end with my 435D, even with both left and right hand side permanently open the noise at both idle and 2000 rpm (stationary) were slightly quieter than standard (measured with a spectrum analyser). No issues when driving either.

In answer to the other query, I haven't heard a Diesel 30/35D with a backbox delete in person, but would be interested to do so.

[gerrymoore]

I love the back end of the M4 but couldn't afford the fuel costs!! My 435D is almost as fast and averages 48 mpg so I thought I would change the back end looks. I already had the twin exhaust and a single sided diffuser.

I removed the diffuser and cut out the same size 'hole' as the other side and then used filler to build up around it the same as on the left. Painted it gloss black and sprayed with clearcoat - cost about £8.00.

I sent for two 70mm chrome 'end pipes' on Ebay and some various screws cost £17.00. I'm OK with a welder so I made a bracket to fit on to the existing 12mm bolt holding the silencer on and bolted the bracket to this bolt. After a bit of messing about I've got it almost right but still needs a bit of tweaking to get them exactly the same.

Doesn't make any difference to sound but looks better!

[420dbal]

Originally Posted by gerrymoore

I love the back end of the M4 but couldn't afford the fuel costs!! My 435D is almost as fast and averages 48 mpg so I thought I would change the back end looks. I already had the twin exhaust and a single sided diffuser.

I removed the diffuser and cut out the same size 'hole' as the other side and then used filler to build up around it the same as on the left. Painted it gloss black and sprayed with clearcoat - cost about £8.00.

I sent for two 70mm chrome 'end pipes' on Ebay and some various screws cost £17.00. I'm OK with a welder so I made a bracket to fit on to the existing 12mm bolt holding the silencer on and bolted the bracket to this bolt. After a bit of messing about I've got it almost right but still needs a bit of tweaking to get them exactly the same.

Doesn't make any difference to sound but looks better!

That looks great, Do you have any photos of the work you did so I can have a go too?

[gerrymoore]

Hiya..thanks!! I did do some photos of the work I did on the diffuser but it's all down to how skilful you are with the filler. I'm not a perfectionist so all I did was cut out a space the same as on the left and then built up around with the filler. Sanded down a few times as I was going along and then primed and painted - still got to lacquer it yet!

The pipes were off EBAY 2 x 70mm o/d chrome ends. I used some stainless banding to keep them together. On my car (2017 435D) there is a long 12mm bolt holding the rear silencer to the chassis. I made a bracket to fit this and then used a long 6mm bolt to attach the pipes.

It's not very pretty from underneath but looks OK from above....and very cheap!

Off topic but I had it stage 1 mapped a couple of weeks ago now 365bhp and 720nm torque but can't use it now with this darned virus!!

[420dbal]

Wow, that is really skillful work! I don't think I could manage something like that so kudos to you
This Virus is really terrible. But, Great to hear about the remap. Where did you get it done?

[gerrymoore]

A guy near Chester did it for me. I've only driven it twice since and didn't even get into Sports mode...mind you 'comfort' mode is now like the old 'sport' mode....

[420dbal]

Originally Posted by gerrymoore

A guy near Chester did it for me. I've only driven it twice since and didn't even get into Sports mode...mind you 'comfort' mode is now like the old 'sport' mode....

Nice I do think about how it would have been getting the 6 Cylinder but it was hard to find the spec I wanted. I do really love the 420d and will just tweak it over time to get the best out of it.

[Fez_7]

As it's a similar topic I'll post here rather than starting a new thread. Got a F30 320d so yeah diesel again and I know it's not going to sound amazing but only got the single tailpipe on the left and looking to get it converted to a twin tip on the left only (rather than dual conversion).

Not sure whether to just get the tailpipe only welded on or get the backbox deleted too. Another option is to swap my current setup with that of the 335d so I still have a backbox but with the twin tailpipes. Would the 335d option make any change in noise?

Would be great to get some feedback on this as I've no experience with exhaust mods. I'm thinking of opting for the backbox delete after watching YouTube videos too but don't want to regret it if I find it drones on the motorway. Just hoping for a slightly sportier noise but nothing major to upset the wife and baby!

[IAmATeaf]

@gerrymoore so the pipes on the right are not functional just fake?

[gerrymoore]

Iamateaf....Yes just fake - sorry! But it looks amazing for £25!!

Fez ..I don't think changing the pipes will give you any better sound as diesels are diesels........the back box delete would just make the same sound only louder!

My car has the BMW ASD which is supposed to make it sound more like an M4 but I can't really hear it. I have tried reprogramming with Carly but still not much better ...think my next car will be a real M4!! I do so little mileage now that the mpg won't really make any difference.

420Dbal...my last car was an F30 320D. I had it stage one remapped and it was absolutely amazing...like sport mode in comfort but a different animal in sports mode...I paid £200 and it was money very well spent!!!

[Fez_7]

Originally Posted by gerrymoore

Iamateaf....Yes just fake - sorry! But it looks amazing for £25!!

Fez ..I don't think changing the pipes will give you any better sound as diesels are diesels........the back box delete would just make the same sound only louder!

My car has the BMW ASD which is supposed to make it sound more like an M4 but I can't really hear it. I have tried reprogramming with Carly but still not much better ...think my next car will be a real M4!! I do so little mileage now that the mpg won't really make any difference.

420Dbal...my last car was an F30 320D. I had it stage one remapped and it was absolutely amazing...like sport mode in comfort but a different animal in sports mode...I paid £200 and it was money very well spent!!!

Cheers Gerry. I've spoken to a couple custom exhaust specialists who said backbox delete won't make any change in noise as the silencing is already done further up the exhaust so think I'll just go down that route to get my twin tips as it'll be cheaper than buying a 335d backbox and getting that welded on.

I've also got a F30 320d stage 1 remapped with EGR delete and would highly recommend it. Paid £250 for mine with dyno tests and fully agree it was money well spent! Mine is the ED model so 163bhp standard, now just shy of 240bhp and over 480nM torque

[gerrymoore]

I've made a few more mods to the car whilst twiddling my thumbs in the lockdown. I've fitted an M4 flat bottomed leather and alcantara steering wheel (fantastic) and wrapped a lot of the interior in carbon fibre type material. Hard going at first but got better as I went on.......pleased with the results though. I've also fitted 12mm spacers to the rear wheels to fill the arches better.