OEM Exhaust Back boxes size

A

Adelphi2

Member
Hi,

Does anyone know the dimensions of the OEM Exhaust back boxes on the Z4M? I need length, width and height please if possible. Thanks.
 
Length =40cms
Width = 40cms
Depth = 15cms

That's the silencer part (i.e. cans) and doesn't include the appendages of the inlet pipe and tail pipes. :thumbsup:
 
If it helps here's a picture of a set when I was mocking up designs to fit them, move the battery and add CF diffuser onto mine:

DSC02690.jpg
 
Yes, I'm wondering what's the point of fitting these silencers? You'll be adding a minimum of 6kgs to a non ///M car and I doubt if it will improve the sound.
 
exdos said:
Yes, I'm wondering what's the point of fitting these silencers? You'll be adding a minimum of 6kgs to a non ///M car and I doubt if it will improve the sound.
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I fitted them and with replacement slim performance battery and removal of carbon filters there was no net gain.
Sound on mine is much improved.

I don't make any claims on performance but it does feel better.
 
Adelphi2 said:
exdos said:
IMO, you'd be better off gutting a pair of your OEM silencers for performance and sound.
Click to expand...

Ooohh really? Define "gutting" please.
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Open the silencers on the upper surface and remove the pipework and reconfigure. The objective is to remove any "reverse flow" which allows the exhaust gases to exit the system faster because there's less resistance to flow. The photos below are what I've done to the silencers on my Z4MC.

IMG_8076.jpg


Guttedsilencer_zps2f525001.jpg
 
Very very interesting. Really it begs the question of why was it designed that the exhaust flow should go back in on itself and then exit? Is there a pressure differential that is at work here? Any emissions change that is apparent from removing the piping?
 
I thought the reserve flow chambers were to dampen the sound, hence the term silencer/muffler?
 
Adelphi2 said:
Very very interesting. Really it begs the question of why was it designed that the exhaust flow should go back in on itself and then exit? Is there a pressure differential that is at work here? Any emissions change that is apparent from removing the piping?
Click to expand...

As Ranski says, reverse flow is commonly used for silencing, but the fact that BMW do this in the Z4M by keeping the exhaust gases within pipework, much like a trumpet or trombone does, is different to the usual way of doing this. The Z4M OEM silencers are actually pretty good as they are but by removing the pipework, as I've done, makes them flow better but it also reduces the silencing a bit too. :D

I've never had any problems with emissions from gutting silencers and the silencers on my Z3MC are much more radically gutted than those on my Z4MC, and they've passed the MOT each year with no problems at all for the past 6years. :thumbsup:
 
I've had 'straight through' silencers fitted to the 'M' for five years with a resonator delete as well. Gases basically travel from the cats and straight out the end pipes. That's as 'straight through' as you can get for a system and the car's never had any engine management issues or missd a beat over 30+ thousand miles.

No idea if it enhances power or not but the car sounds good!
 
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