10 replies to this topic

[oliver122]

hey guys , ive got a fibreglass bonnet fitted on pins on my mini , now i was wondering how i would go about putting sound deadening on it with it being fibreglass . also im after some closed cell foam to put on the internal bulkhead , was wondering what people used .

 

cheers 

[Skortchio]

With a fibreglass bonnet you'll likely notice more of an improvement from some sound deadening than a steel bonnet, which is good for you!

 

Contact adhesive (screwfix) is good stuff for attaching it and if you check out this ebay seller:

 

http://www.ebay.co.u...=item460e32b2fc

 

This is who I bought all my foam from, was good value and did the job nicely.

[oliver122]

cheers for that , will the adhesive cope with the heat and are you saying use that stuff under the bonnet ? 

[Skortchio]

Mine has stayed on using the same method, that's on a painted steel bonnet but in terms of adhesion it seems fine. Give the surface to be bonded to a good clean first with a scotch pad.

 

Of course don't put the foam below the crossmember where the exhaust headers are but it shouldn't have trouble dealing with the engine bay temps.

A lot of the sound comes through your windscreen, short of sound proofing that the bonnet is a good option :)

[oliver122]

cheers for that , i wasnt to sure if you meant to put that inside the car and whatever i was going to use under the bonnet stick with contact adhesive . thanks for you help

 

by any chance do you have a picture of your bonnet done ? , cheers

Edited by oliver122, 01 May 2013 - 08:49 AM.

[Sam Walters]

Well generally to quieten a car down you increase mass to help absorb energy. Why not add more fiberglass to the underside of your bonnet?

[Skortchio]

Mass loading is more akin to reducing resonance in the panel itself, the closed cell would be to promote sound blocking and absorption in this case.

 

If you're finding the bonnet is vibrating then you could add a layer of butyl based mass loader before any blocker but being f/g I wouldn't imagine it's needed if you lock it down sufficiently.

 

Haven't got a pic of the bonnet itself, but you can see it (ish) in this shot.

 

[Sam Walters]

Do remember. Foam in an engine bay!

Thats why i mentioned more fg.

[Skortchio]

It must be early, I'm missing your point.

 

We're not talking polystyrene here, ccf is unlikely to melt from bonnet temps unless it's put onto the exhaust manifold and it doesn't absorb moisture so why is it unsuitable?

 

F/G doesn't really have great blocking or absorption properties, if it did we wouldn't need to line speaker pods with mass loader and noise killer surely?

 

I'm interested to understand the merits of f/g as a damping or agent though.

[Sam Walters]

High frequencies tend to reflect from fiberglass. This would then manifest its self in the form of sound from the cone.

Mass loaders and foam noise barriers stop this reflection.

Some of the more extreme lot whom do SPL will cover floors and other places with FRP.

But these cars are likely to be destroyed beyond repair during the events. I doubt chucking FRP onto the floor of your mini would be a wise move.

 

So of course mass loaders will work they add mass but wont half as well as blocking noise as fiberglass will.

Edited by Sam Walters, 06 May 2013 - 10:43 AM.

[Ruckus]

To keep the weight down i would use a proper sound deading material like Dynamat or Silent coat. These are not 'just' mass loaders...

 

And then an insulator like Dynaliner.

 

http://www.deadening...k-dyn10425.html

 

 

http://www.deadening...4-dyn11102.html

 

This will not be cheap though.

 

if you want to do in cheaply (but heavy) as Sam says just add more FRP.