45 replies to this topic

[gazwad]

The mini can be made quiet and refined, like any other car. My mini is as quiet at 70mph as my wife’s alfa romeo mito (actually slightly quieter!). Most people tend to go about it the wrong way though. Starting with the engine, use the standard air box or a remote enclosed induction kit, the exhaust can be a performance one but needs to be twin box and the largest silencer boxes possible (mine is a maniflow system with the extra large boxes) also the exhaust should use the later injection mini hangers as these transfer much less vibration than the bobbin type. Engine mounts can be improved using oem mounts on the bottom and modified top engine steady using a larger bush from a more modern car makes a huge difference, a flexi joint on the exhaust is a good idea to allow for a slight increase in engine movement. Next is soundproofing, another area where people tent to invest in the wrong materials. Dynamat etc type stuff will make very little difference, only a small amount is needed in the middle of larger panels to reduce drumming. Make sure all holes/gaps are blocked on bulkheads etc, then the stuff that actually makes a noticeable difference is mass loaded vinyl over a layer of foam, something like 6mm thick foam and i like to use tecsound 50 mlv as its better value and more effective than a lot of automotive brands. This has to cover the whole floor and bulkheads to be effective.

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The mini can be made quiet and refined, like any other car. My mini is as quiet at 70mph as my wife’s alfa romeo mito (actually slightly quieter!). Most people tend to go about it the wrong way though. Starting with the engine, use the standard air box or a remote enclosed induction kit, the exhaust can be a performance one but needs to be twin box and the largest silencer boxes possible (mine is a maniflow system with the extra large boxes) also the exhaust should use the later injection mini hangers as these transfer much less vibration than the bobbin type. Engine mounts can be improved using oem mounts on the bottom and modified top engine steady using a larger bush from a more modern car makes a huge difference, a flexi joint on the exhaust is a good idea to allow for a slight increase in engine movement. Next is soundproofing, another area where people tent to invest in the wrong materials. Dynamat etc type stuff will make very little difference, only a small amount is needed in the middle of larger panels to reduce drumming. Make sure all holes/gaps are blocked on bulkheads etc, then the stuff that actually makes a noticeable difference is mass loaded vinyl over a layer of foam, something like 6mm thick foam and i like to use tecsound 50 mlv as its better value and more effective than a lot of automotive brands. This has to cover the whole floor and bulkheads to be effective.

Great input thanks very much.

Going for the most cost effective changes so my immediate to do list is now

1. Standard air box going on today

2. Get later exhaust hangers ordered

3. My soundproofing efforts so far have only reduced interior noise by around 7db compared to a fully stripped out car, so I'd say silent coat / carpet underlay foam combo hasn't achieved much.
Tecsound will be ordered and initially installed across full bulkhead before adding elsewhere.


Finally, can you or someone else advise on how to modify the engine steady to accept larger bushes? I've noted that I'll need a flexi on the exhaust

Cheers for the help so far everyone, amazing where a chat about engine mounts leads!

[MiniCarJack]

I've only casually flicked through this thread so it may have already been mentioned, but it's worth adding some insulation / soundproofing to the underside of the bonnet as well, it can resonate quite a lot with engine vibrations as the bonnet skin is quite flexible and basically acts like a drum, so addressing this might help to further reduce engine noise for you. Also consider fitting a rear bonnet gutter seal if you haven't already got one, that can help a little.

 

Interested to see how much of a difference you manage to make with all your changes, as I'll be going through my daily driven mini in the near future in an attempt to achieve similar results in refinement and quiet(ish)ness!

[ads7]

Good idea re underbonnet I'll get that done in due course.

Already have rear gutter rubber in place.

Just to recap I'm measuring at each stage with a sound meter, as today's mod is standard air box I will post up dB reduction. Should take away a lot of racket

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Now down to 85 decibels with std filter box. Perceptibly quieter but still some way to go.

Wishing you all a happier 2021

[Cooper Mac]

Just reading back where you started out, from 96 to 85 is a huge reduction!!

Measuring noise and sound pressure is not easy, and this works on a log scale, so normally when working in dbA ( A weighted to simulate what the human ear can hear), an increase of 3 dbA is basically a doubling of the power intensity.

Ads, you have quoted the measurements in dB, so this is a little more difficult to equate to what the human ear will hear. If you really have recorded the sound in dB, then it is possible that you may have reduced some frequencies, but that the frequencies within the range of human hearing may have remained unchanged. Just something to bear in mind!

I think I mentioned before, that when measuring the sound, all variables need to be the same in order to have understandable readings. I know from trials that having the noise meter set at a 2 different distances only 10mm apart will give a different reading.

The main test will be if you can bear being in the car for any length of time. The things you have done so far will all help, the air box especially!

Keep up the good work and happy 2021!

[ads7]

Happy 2021!

Yes the only variable I didn't consider was the precise placement of the sound meter, everything else in the car was constant even down to wearing the same clothes.

Still getting more induction roar than I would have wanted perhaps because I drilled four holes at the front underside (usual place for this mod)

Before now I'd relocated the ramair filter to behind the grille linked by 60mm plastic trunking to a rover v8 Carb elbow attached to the Hs4. That moved the induction roar right away. Might try that again for comparison.

Just going to enjoy the car on short local journeys (currently in tier 3) for a few days now to see how I feel about everything I've changed so far.

[Dusky]

You can also further reduce noise by adding lizardskin on the firewall.

[Trav.al.er]

Hi there. I've always wondered if clamping a heavy weight around the engine steady bar would reduce the transmission of vibration into the baulkhead. I'm thinking that by using different weights it may be possible to tune the frequency to somewhere less anoying, ie away from your favoured cruising speed. Alan.

[ads7]

A novel approach, some one on might have an expert viewpoint to offer?

Currently there's a hiatus on the nvh experiment due to lockdown .. next job is to suspend the exhaust using softer hangers as previously suggested

[sonscar]

My elderly KIA has random large lumps of iron bolted to the engine in seemingly random places and my previous Citroen also had these so there must be something to be gained if you could calculate the size/position.Steve..

[ads7]

The mini can be made quiet and refined, like any other car. My mini is as quiet at 70mph as my wife’s alfa romeo mito (actually slightly quieter!). Most people tend to go about it the wrong way though. Starting with the engine, use the standard air box or a remote enclosed induction kit, the exhaust can be a performance one but needs to be twin box and the largest silencer boxes possible (mine is a maniflow system with the extra large boxes) also the exhaust should use the later injection mini hangers as these transfer much less vibration than the bobbin type. Engine mounts can be improved using oem mounts on the bottom and modified top engine steady using a larger bush from a more modern car makes a huge difference, a flexi joint on the exhaust is a good idea to allow for a slight increase in engine movement. Next is soundproofing, another area where people tent to invest in the wrong materials. Dynamat etc type stuff will make very little difference, only a small amount is needed in the middle of larger panels to reduce drumming. Make sure all holes/gaps are blocked on bulkheads etc, then the stuff that actually makes a noticeable difference is mass loaded vinyl over a layer of foam, something like 6mm thick foam and i like to use tecsound 50 mlv as its better value and more effective than a lot of automotive brands. This has to cover the whole floor and bulkheads to be effective.

Hi, back onto this project now, very interested in how exactly you made your modified top steady? What bush did you use etc ?

[Spider]

Another possible approach here might be to fit a noise cancelling system. I know it has been done of some 'spaces' (I'm just trying to remember where I have read of it), I've no idea if this would be a practical approach or not ?? There's others here who I'm sure would have some experience with such systems (Cooper Mac ?). If you've ever tried Noise Cancelling Headphones, you'll appreciate how effective the system can be.

 

<Edit: After posting this I just had a google to see if anything existed. There's actually many on the market, some even specific for inside vehicles, eg

https://www.silentium.com/        >
 

Edited by Spider, 17 August 2021 - 09:18 PM.

[ads7]

Spider, good outside the box train of thought. Silentium seem to do trade to trade products although there may be a b2c product offered by someone

[whistler]

 

Haha yes these type of discussions normally conclude along the lines that Minis are just noisy, however I do think that thicker lower engine mounts alone would make a real improvement and wouldn't be hard to engineer.

You could probably use an automatic front subframe to get more room as they are wider between the engine mounts.

 

Seems like a lot of work for very little gain though to me.

 

Some race and hill climb minis use the auto subframe so as to lower the engine/gearbox.