QUOTE(Literati914 @ Apr 25 2021, 04:49 PM)
I've had two 914s with stock engine side pads.. both just seemed like loose-fitting, worn out rubber sheeting to me.. I didn't notice any layers to them. Maybe those were something other than stock
, IDK.. then the other side (you mean the back-pad side?), neither cars had anything between the back pad and fire wall. I'm sure layering would be effective at noise tho. Maybe dynamat on both sides?
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Then you have tar pad, steel, tar pad...IMHO that's wrong.
You need a tar pad, steel, foam pad and then rubber pad. Maybe use some heavy rubber roof liner, but I don't know if that material is fireproof enough.
The dynamat will work as part of the sandwich, as does the stock back pad. The engine bay has to have something that replicates the stock pad. You could try stripping out the horse hair for the stock pad and glueing in something like a closed cell foam.
I'm no sound engineer but anecdotally I know it's the sum of the layers that reduces noise, not any one layer. BTW also make sure the glass is sealed.
My /6 conversion I used the stock backpad, but I reglued it and made sure the big plastic washers were secure. I now notice that the mid-seam each side is starting to loosen so I plan to secure them as well, maybe with a strip of 1/8" alunimum.
My weber carb /6 is not noisy at cruise, you can easily have a conversation without shouting and there's no drone. But the engine is loud, so I know the sound deading is for sure working.