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· Registered
05 XT2.5
1,976 Posts
Discussion Starter · #1 ·
I had some dynamat stuff left over and I was going to do under the bonnet. Then I got worried about a bit falling off and going somewhere it shouldn't. Then I was working in the bathroom and to fill a hole I used some of that spray foam. Then I thought I know - I'll used the rest to soundproof the bonnet.

To me the bonnet is designed like an acoustic guitar - 2 bits of something with a space between them and a hole (or 3) to let a small amount of sound in, get amplified and come out again.

So I gaffa taped over as many of the holes as I could and started squirting the stuff in. It expands like crazy and gets anywhere it can - I used an old sheet over the engine and the inner wings. Then I left it 30 mins to go off then I drove it. As soon as you start the motor you can hear it's worked - in fact as soon as you close the bonnet the 'clunk' sound tells you it's done something. Cruising at 60 ish the difference is really surprising. I suffer from the drone of a loudish exhaust but it's much reduced - somehow the foam seems to have disconnected any noise from the front from the noise at the back and stopped a resonance that was going on. Anyway I can hear the stereo quite well on 17 or 18 - it used to be on 24 or louder before.

If you have an engine comartment that it a thing of beauty you might not want to do this. I have some foam sort of bulging out here and there but I'll trim it off and put a bit of black paint over it or something.

Wondering where else I can use it now.

· aka DMax in Alaska
'06 Mini Cooper S JCW 6MT
639 Posts
That is a great idea! The concern I would have would be that the inner portion of the hood would be forced apart from the outer skin as the foam expands. Did you notice anything like that? Any bulging?
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