45 replies to this topic

[cal844]

I wouldn't use exhaust wrap on an LCB or Free flow type exhaust manifold as it will get too hot and bend, cracking is also a possibility.

There are various threads regarding this.

Hope this helps

Edited by cal844, 16 November 2020 - 10:36 PM.

[nicklouse]

Closed cell is not that good as a stater. You need to add mass to the bulkhead to change the resonate frequency. You then add close cell to help reduce sound transfer. 
 

don’t wrap the exhaust it can kill them due to embrittlement it also just moves the heat to the center tunnel that can start mending things.

filling the bulkhead with foam will just increase rust issues as it is not a sealed unit. Making sure it is closed off to the engine bay helps.

. 

[Cooperman]

In the 60's there was a kit called 'Interior Silent Travel' (or something similar). It did quieten the inside but, in the end, a Mini will never be quiet like more expensive and larger cars.
It is possible to get a Mini to be quieter, but there may be trade-offs. For example, the rubber front sub-frame will make for a slightly quieter ride but with poorer steering response. More sound insulation will increase weight. You just need to find the compromise which best suits you.

Edited by Cooperman, 17 November 2020 - 12:11 AM.

[ads7]

I wouldn't use exhaust wrap on an LCB or Free flow type exhaust manifold as it will get too hot and bend, cracking is also a possibility.

There are various threads regarding this.

Hope this helps

Point taken thank you

[ads7]

In the 60's there was a kit called 'Interior Silent Travel' (or something similar). It did quieten the inside but, in the end, a Mini will never be quiet like more expensive and larger cars.
It is possible to get a Mini to be quieter, but there may be trade-offs. For example, the rubber front sub-frame will make for a slightly quieter ride but with poorer steering response. More sound insulation will increase weight. You just need to find the compromise which best suits you.

Thanks Cooperman, refinement isn't an intrinsic feature of these little cars so I'm only ever going to dial out so much NVH. On the positive side customising Minis to suit our personal taste is simple and fun.

I should have started this forum thread with WHY I'm bothering - two reasons really.

One, my wife is suffering more discomfort lately due to having MS, so making the little car she loves more refined is now the priority.

Two, I've slowed down in my middle age and want more refinement so a little luxury appeals. I'm reading up on Radford and Wood and Pickett quite a bit lately not that I'll be going too far down the luxury route just a few steps in that direction over time.

I'm looking to make this a cost effective exercise that defines which action brings the best result per pound spent.

I can't afford to install loads of silentcoat/Dynamat throughout but will be adding some of it to the inside of the bulkhead to add mass there. My car is a an '86 City so still has most of the factory bitumen on the floorpan.


Thanks everyone for your advice so far. Starting work this week.

[Cooper Mac]

 

Having worked in NVH, I'm interested to see how this progresses.

ads7, what sort of noise meter have you bought? Is this a handheld meter, or can this be plugged into an analyser to record and play with the results? Recording and comparing noise readings is difficult unless you have access to an anechoic chamber. If you are recording the noise as you drive, then this is difficult from within the car, because of it's size and the reverberation of everything inside the car. You would also need to have all parameters exactly the same on every test, speed, engine revs, position of noise meter, what you wear!

Changing the engine mounts might make a difference due to different grades of materials etc, but it will generally be what the mount is bolted to (the subframe) that will determine the audible noise. In the case of the top engine steady, the noise is amplified by the fact that the steady is fixed to the bulkhead, which acts as a sounding board. The 'sound' from this mount is reduced by fitting OE bushes as these are softer and therefore damp the vibration seen at the bulkhead, less vibration of the sounding board = less noise. If you put poly bushes in this top mount, the vibration is damped less, and therefore transmits more vibration into the bulkhead sounding board = more noise.

Unless you have already done it, I think fitting sound deadening to the bulkhead would be the first thing to do to damp and change its natural frequency.

Thanks for your professional input that's absolutely invaluable.

Just using a cheap noise meter measuring decibels.

I was going to run the car in fourth gear at around 52mph where the resonance is at its worst (just wiring in a rev counter to give more accuracy) on the same stretch of road after each change/mod with weather as similar as possible given the British climate.
Imperfect, but some controls in place.

I've just ordered one piece mpi spec engine steady rubbers.

Would filling the bulkhead cross member with expanding foam help reduce noise to any degree?

I'm running solid top front subframe mounts which will revert to rubber.

Free flow tubular manifold is fitted and will have exhaust wrap applied.

I've already fitted closed cell 10mm foam to the majority of the bulkhead, expect I'll need to add extra soundproofing to compliment this.

So an imperfect experiment. Any more helpful suggestions much appreciated as I'd like to help people address the problem effectively within the constraints of a modest budget.

Thanks Adam

 

Hi Adam,

 

To be honest, you might be wasting your time with the noise meter, but it might be worth a go out of curiosity! If you can set the meter to read dBA, then this will give you an 'A' weighting to the sound pressure, which will represent what the human ear is capable of hearing.

 

I wouldn't use expanding foam anywhere on the car, as this will trap moisture and rot the car even quicker! I have used expanding foam in an experiment (not on a car) but it did nothing to reduce the noise.

 

If you are getting a resonance at 52ish mph, then changing mounts etc will not help (although I would fit softer bushes in the engine to bulkhead steady) as it is most likely to be a resonance. The way of moving the resonance (you can't eliminate it all together, just move it to a different frequency) is to change the stiffness / natural frequency of the panel which is resonating. The  As Nick said, you need to change the mass of what ever is resonating (probably the bulkhead / toeboard???) by adding or taking away mass. It'll be easier to add mass, but this may just move the resonance to a different (lower) rev / speed range. The other way to change the stiffness is to a ribs or brackets, but for a car that just isn't easy!

 

The resonance of the panel will 'excited' when some other variable on the car has a frequency that matches the panel. So in terms of a car, there is usually a source of variable frequency, that can excite different parts of the car at different times. This source of variable frequency will but related to the engine / drivetrain /wheels, which all have variable rotational frequencies with varying speed. Balancing of rotating parts is always good for reducing vibration, wheels are cheap and easy, but engine parts, no so, unless you are having an engine rebuild, in which case that is the ideal time to get these parts done.

 

Personally I would keep the solid top mounts on the subby, as this will not add too much to the noise, but will give better handling, assuming all the other front mounts are solid?

 

You say that you want a cost effective solution, well I would say that a cost effective solution would be to use a sound deadening material, Silent coat etc. Contrary to popular belief, you do not need to cover every square inch of the car in the sound deadening, all you want to do is make the panels 'dead' when you bang them, it is not a 'sound proof' material. All you need to do is add a bit to each panel, then cover with closed cell foam. I wouldn't bother playing with engine mounts etc until you have changed the resonance. This is probably the best route to go, but without witnessing it myself it's hard to say! 

[ads7]

Having worked in NVH, I'm interested to see how this progresses.

ads7, what sort of noise meter have you bought? Is this a handheld meter, or can this be plugged into an analyser to record and play with the results? Recording and comparing noise readings is difficult unless you have access to an anechoic chamber. If you are recording the noise as you drive, then this is difficult from within the car, because of it's size and the reverberation of everything inside the car. You would also need to have all parameters exactly the same on every test, speed, engine revs, position of noise meter, what you wear!

Changing the engine mounts might make a difference due to different grades of materials etc, but it will generally be what the mount is bolted to (the subframe) that will determine the audible noise. In the case of the top engine steady, the noise is amplified by the fact that the steady is fixed to the bulkhead, which acts as a sounding board. The 'sound' from this mount is reduced by fitting OE bushes as these are softer and therefore damp the vibration seen at the bulkhead, less vibration of the sounding board = less noise. If you put poly bushes in this top mount, the vibration is damped less, and therefore transmits more vibration into the bulkhead sounding board = more noise.

Unless you have already done it, I think fitting sound deadening to the bulkhead would be the first thing to do to damp and change its natural frequency.

Thanks for your professional input that's absolutely invaluable.

Just using a cheap noise meter measuring decibels.

I was going to run the car in fourth gear at around 52mph where the resonance is at its worst (just wiring in a rev counter to give more accuracy) on the same stretch of road after each change/mod with weather as similar as possible given the British climate.
Imperfect, but some controls in place.

I've just ordered one piece mpi spec engine steady rubbers.

Would filling the bulkhead cross member with expanding foam help reduce noise to any degree?

I'm running solid top front subframe mounts which will revert to rubber.

Free flow tubular manifold is fitted and will have exhaust wrap applied.

I've already fitted closed cell 10mm foam to the majority of the bulkhead, expect I'll need to add extra soundproofing to compliment this.

So an imperfect experiment. Any more helpful suggestions much appreciated as I'd like to help people address the problem effectively within the constraints of a modest budget.

Thanks Adam

Hi Adam,

To be honest, you might be wasting your time with the noise meter, but it might be worth a go out of curiosity! If you can set the meter to read dBA, then this will give you an 'A' weighting to the sound pressure, which will represent what the human ear is capable of hearing.

I wouldn't use expanding foam anywhere on the car, as this will trap moisture and rot the car even quicker! I have used expanding foam in an experiment (not on a car) but it did nothing to reduce the noise.

If you are getting a resonance at 52ish mph, then changing mounts etc will not help (although I would fit softer bushes in the engine to bulkhead steady) as it is most likely to be a resonance. The way of moving the resonance (you can't eliminate it all together, just move it to a different frequency) is to change the stiffness / natural frequency of the panel which is resonating. The As Nick said, you need to change the mass of what ever is resonating (probably the bulkhead / toeboard???) by adding or taking away mass. It'll be easier to add mass, but this may just move the resonance to a different (lower) rev / speed range. The other way to change the stiffness is to a ribs or brackets, but for a car that just isn't easy!

The resonance of the panel will 'excited' when some other variable on the car has a frequency that matches the panel. So in terms of a car, there is usually a source of variable frequency, that can excite different parts of the car at different times. This source of variable frequency will but related to the engine / drivetrain /wheels, which all have variable rotational frequencies with varying speed. Balancing of rotating parts is always good for reducing vibration, wheels are cheap and easy, but engine parts, no so, unless you are having an engine rebuild, in which case that is the ideal time to get these parts done.

Personally I would keep the solid top mounts on the subby, as this will not add too much to the noise, but will give better handling, assuming all the other front mounts are solid?

You say that you want a cost effective solution, well I would say that a cost effective solution would be to use a sound deadening material, Silent coat etc. Contrary to popular belief, you do not need to cover every square inch of the car in the sound deadening, all you want to do is make the panels 'dead' when you bang them, it is not a 'sound proof' material. All you need to do is add a bit to each panel, then cover with closed cell foam. I wouldn't bother playing with engine mounts etc until you have changed the resonance. This is probably the best route to go, but without witnessing it myself it's hard to say!

Thanks again!

I'll set the meter to dba then

So.. soft engine steady mounts first, add mass to bulkhead second and go from there!

[ads7]

Silent coat ordered.

[Spider]

Our locally produced Clubman GTs were considerably more quite than any other model made here.

 

They had Hydolastic suspension, which I've always found dampens road noise quite a bit.

 

The other thing they did was to fit carpet underlay everywhere, so much so, that not only were these the quietest Mini we had, but also the heaviest, though not all of that could be attributed to underlay !

[ads7]

I've got a double layer of carpet already which will help.

Ebay sound meter, silent coat pads and ducting to relocate ramair foam filter away from carb mount far away behind grille are due in post very soon.

I've set up a new Instagram account. For some reason the followers are just starting to ramp up, I don't know why. Anyway link to that below

https://www.instagra...id=pv54nyc4ayvu

So with this little experiment I'll post up sub 1 minute videos on Insta, with the longer videos living on my YouTube channel

https://youtu.be/uQhXRFexwks

I'll doing my best, apologies for the total lack of slick production values!

[nicklouse]

 

relocate ramair foam filter away from carb mount

 

FFS. Fit the old housing back on with a suitable filter element like the KN one. This will be one of the biggest reductions in noise. The 90 degree bend does wonders in moving sound waves. 

[ads7]

I know I know.. this is the time honoured way. Will be very likely to move to that setup with the six holes drilled into the front of casing in the appropriate place.

Air filter first change then its on to moving/reducing other sources of noise and resonance.

[ads7]

relocate ramair foam filter away from carb mount

FFS. Fit the old housing back on with a suitable filter element like the KN one. This will be one of the biggest reductions in noise. The 90 degree bend does wonders in moving sound waves.

Housing and K & N filter duly won on Bay of e.

Can't say it'll help the engine bay look good but focused on refinement now and acting on good advice on TMF.

Just a few more bits due in post next week then I can crack on with the experiment

[ads7]

Some progress made.

For a start point I stripped car out except for front seats. peak interior noise measured at 98db.

Ebay sound meter set to DBa, calibration may be out, ultimately whatever the readings its the percentage improvements that count.

Next I spent a day adding mass: 4x silent coat 10x12" sheets full coverage across upper bulkhead, a few strips across parcel shelf and rear seat back.

A lot of noise from the lhs air vent due to fan and timing chain rattle addressed by blocking vent off with closed cell foam.

Then old closed foam backed carpet reinstalled, had open cell foam carpet underlay in abundance available due to a recent house flood, duly installed on whole of bulkhead and on top of original floor carpet, topped with a new carpet.

Interior is now looking much posher mainly cream and beige.

Obviously noise is reduced but still harmonic vibration to address, engine steady bushes next on to do list.

Air filter element arrived from bay of e, turned out it was for a Hs2 not Hs4, so need to get a hold of the right parts at a reasonable price which may take a while. Casing and element even secondhand cost as much as I used to pay for a whole Mini back in the day!

[ads7]

Still need to address vibration harmonics at certain points in the rev range.

Today I swapped in a new oe spec offside engine mount and a top steady bush late mpi one piece affair. All of which made no discernable difference which was disappointing.

Next jobs:

Swap in rubber front subframe tower bolts thick spacer/washer replacing the solid aluminium one currently in place. All other subby mounts are rubber.

Oe air filter box in place of existing ramair open foam filter.

Really should go back to original cast exhaust manifold as I believe the mild steel freeflow I have now resonates a lot I may consider this when the one fitted finally drops to bits.

Finally I could go the whole hog and fit a two box system although the single mk1 sprite (frog eye) one I have now sounds perfect with a nice sublty sporty note.

The only other thing I can think of are more silent coat pads to add mass in key areas. Behind dash, whole floor seat back and parcel shelf are already done.

I'll use the sound meter to quantify each change.