Sound generator temporary delete

[Spriteracer]

Hi all,
I have a late 2006 3.0si coupe and I am finding the drone on the motorway, cruising at 65-75 very wearing. (I'm currently doing about 500mls a week of which 90% is motorway).

I appreciate this will be anathema to many on here, however I am looking at trying to reduce the drone and suspect changing the inlet ducting and sound generator for one from the 2.5 without the SG will improve matters.

My question is - are the diameters of the ducts, bellows etc. the same for both ? Looking at the graphics and part numbers on BMW supply, they seem to be, however the non SG bellows is not referenced on the 3.0Si page, so it is not exactly clear. eg.

https://bmwsupply.co.uk/part/details?series=e85&typ=bu31&og=01&hg=13&bt=13_1173&view=btdetail
https://bmwsupply.co.uk/part/details?series=e86&typ=du51&og=01&hg=13&bt=13_1173&view=btdetail

Alternatively, has anyone tried the Samco hoses route ? - 2 bends and a joiner - as has been suggested by my Z4 owning indy. I recon the costs would be broadly similar but I would prefer the more or less straight swap OEM route if possible. I will keep the original with SG for when I come to sell in a few years time.

Many thank for any info.

 

[Paulwirral]

A few years ago I bought a 3ltr roadster off a guy that had done the increased noise mod and the first thing I asked on the test drive was "did you leave the airfilter out when you serviced the car "
I think it sounds terrible but everyone's different , I dismantled the pipe work and blocked it with a domestos plastic bottle top , the red one , it's a perfect fit and won't cost more than a quid , and you can bleach the toilet too :lol:

 

[jabber]

Why not just add more foam into the pipe going into the cabin

 

[Smartbear]

As above, i removed the pipe that goes through into the cabin area & capped off the diaphragm, the last part isn’t really essential though as the air can’t pass through that part so no air leak to worry about
Rob

 

[Liam22]

Alternatively, has anyone tried the Samco hoses route ? - 2 bends and a joiner - as has been suggested by my Z4 owning indy. I recon the costs would be broadly similar but I would prefer the more or less straight swap OEM route if possible.

I have been looking into this option for the race car in the interests of simplicity and having a bit more space in the engine bay. I thought I also might use the hole in the bulkhead for passing battery cables and fire extinguisher hoses.

I found this picture on a US forum.


My primary concern with this approach is the "step" that is introduced with the join. It's probably more disruptive to airflow than the sound generator branch-off. Do we know the outside diameter of the throttle body and airbox outlet? Is it constant?

 

[mr.tourette]

As smartbear has said, just remove the gubbins and cap it off, it shouldnt affect the airflow at all as it only carrying soundwaves down it

 

[Spriteracer]

Thank you all.

It seems much simpler than I was anticipating. Couldn't tell from the parts diagrams if there was a direct connection or not. Just got to find the blind bulkhead plug. Seen it on BMW's own site and from Germany and Lithuania, but will consult my own parts boxes first.

Just a thought - should there be sound insulation behind the plug in the bulkhead where it has not been perforated on the non SG cars ?

 

[Smartbear]

Thank you all.

It seems much simpler than I was anticipating. Couldn't tell from the parts diagrams if there was a direct connection or not. Just got to find the blind bulkhead plug. Seen it on BMW's own site and from Germany and Lithuania, but will consult my own parts boxes first.

Just a thought - should there be sound insulation behind the plug in the bulkhead where it has not been perforated on the non SG cars ?

I didn’t worry about replacing the sound insulation behind the pipe entry hole & couldn’t hear any engine noise after removing the sound generator pipe
Rob

 

[Vornwend]

I have now removed both pieces of foam and I really love the sound although I think it may be leading to higher fuel consumption :wink:

 

[Spriteracer]

Ok - have now removed the sound generator pipe and the diaphragm unit and plugged the end of the inlet ducting with a 5 litre container top, jubilee clip and some silicone. Seems fine and solid - no leaks. Plugged the bulkhead grommet similarly.

Was disappointed to find I still have the drone and resonance - particularly bad around 3k rpm under load - i.e at the usual motorway cruising speed in 6th.

So, I'm wondering if the projecting cavities on the inlet ducting have anything to do with it. Before I junk the whole thing for some simple pipes, does anyone know what they actually do ? I note the non SG version has something similar although not so extreme.

For info, I had the exhaust system / hanging etc checked before I bought the car, so don't think it will be that. It doesn't really sound like it anyway.

?? any known issues with engine or gearbox mounts ?

Thanks for any insight as always.

 

[MACK]

Well you seem to have ruled out the sound generator. But when you say you had the exhaust checked, have they actually checked its not aftermarket or looked at the top of the backbox to make sure no ones been in there and modded it etc... Does seem a little strange this droning issues your having, its normally associated with exhausts with a straight through backbox mod, an aftermarket exhaust or a backbox delete. I've not heard of any other owners experiencing the same on a standard car. However that said (and assuming its a manual) the coupe does use a shorter diff that either the pre/post 3.0i/si verts yet all three use the same gearbox and ratios so the coupe does rev a bit higher for a given speed which could be exasperating the problem.

 

[Spriteracer]

Thanks for that. Yes it is a manual. The exhaust was checked only for hanging correctly and leaks. I will look at the weekend, but due to the fact that nothing else on the car has been touched, and the suspension was in such a state that I have renewed almost all of it, I think it is unlikely that the exhaust will have been modified. An aftermarket cheapy possibly.

The resonance does improve with hard acceleration (classic BM 6 pot sound) or higher or lower speeds / or same speed but in lower gear. The "sweet" spot for the resonance is exactly where I spend most time on the motorway.

Regrettably I seem to have acquired a car with a slight lemon tinge, which is very annoying considering I've bought 6 other BMs over the years, and built and re-built the race car a few times. You would think I would have noticed things like this.... Must have been overcome by the excitement !