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Sound deadening for my "83 SC

I'm hoping to add sound deadening to the interior of my SC to attempt to make the vehicle somewhat more pleasant on longer trips.

My intention is to cover most of the sheet metal from the front firewall to the rear speaker shelf.
I think doing the floors will be relatively straightforward but I'm concerned about doing the area around the rear seats since all of the carpeting in that area appears to be glued to the sheet metal.
Once all of the carpeting has been lifted and the Dynamat (or whatever) has been laid in place will I then just glue the carpeting to the dynamat and call it a day?

Will that procedure work or is there a better way to go about it?
The mat that I expect to use is app. 3mm thick.
Thx,
hughc

Old 09-18-2020, 12:50 PM
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KNS KNS is offline
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Simply adding something like Dynamat to the floor won't be enough. If you look at later cars like the 964/993, they have a foam product with a vinyl type of backing under the carpeting.

On your '83 there is already a sound deadening, Dynamat type of product "glued" to the floors. I would lay a closed cell foam product with MLV (Mass Loaded Vinyl) backing on top of that. I did that for my floors and it reduced road noise a small amount. I also put one inch closed cell foam over the engine shelf behind the seats. A new windshield seal will help cut down on wind noise. New, stock engine mounts will also cut down on NVH a little bit.

I did not want to go to the trouble of ripping up all the rear area carpet but you may decide to do that or not. My '84 is noticeably quieter than it was before but still not as quiet as my 993. If I could make the exhaust quieter (it is basically a stock exhaust) that would make an even bigger difference. It's fairly nice with the windows rolled up.
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1984 911 Carrera

Last edited by KNS; 09-18-2020 at 01:42 PM..
Old 09-18-2020, 01:21 PM
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Thank you for your comments Kurt. It appears the solution may not be as simple as I originally thought.
My sc didn't have any padding on the floor when I received it; only just the floor mats, so I can easily add sound deadening material to the floors without too much effort.

Today I went for a drive on the highway to try and determine exactly what type of noises I was hearing. There is some road noise which may be caused by the A/S tires which I won't be changing in the near future. Then I heard some wind noise which seem to be coming from the doors, but they shut very tight but still, 37 year old rubbers may need changing.
The bulk of the noise seems to be coming from the engine compartment along with a little gear whine so maybe it's time to replace the sound deadening pad on the firewall.
I should have taken care of that last winter when I had the engine out.
I'll see if I can easily access the the rear shelf area and add material in that area but otherwise I'll live with it. I'm really not keen on lifting all of the carpet in the rear seat area.
Thx again
hughc
Old 09-19-2020, 04:18 PM
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KNS KNS is offline
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Hugh,

You can remove the upholstered rear shelf by unscrewing the few screws and lifting the whole piece upward. There is a tab that fits into a slot on the rear wall.

Your floor is probably like most other cars - there is a thin floor mat/carpeting over the bare floor. Unless someone scraped it off there is a thin layer of sound deadener on the floor as well (thinner than Dynamat). Some people will add additional, thicker floor mats over the factory carpet. You will be disappointed if you add Dynamat only.

The engine is usually the noisiest thing in the car. The trans is pretty noisy, too. Foam with MLV is one of the more effective ways to quiet these cars. You can purchase closed cell (CC) foam with an MLV backing.

These cars will never be Lexus quiet but the few steps I did made a noticeable difference. Some people have gone even further for more quiet.
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Old 09-19-2020, 05:16 PM
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[QUOTE=KNS;11032400]Hugh,

You can remove the upholstered rear shelf by unscrewing the few screws and lifting the whole piece upward. There is a tab that fits into a slot on the rear wall.

I've removed the screws holding the rear pad in place along with the speakers so now everything can pivot up but seems to be stuck at the bottom of the rear glass.
Is there something specific holding the rear of the shelf in place? or so I just have to apply more force on the shelf to pull it away from the bottom of the glass area?
Thx.
Old 09-20-2020, 09:38 AM
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Quote:
Originally Posted by hughc View Post
Is there something specific holding the rear of the shelf in place? or so I just have to apply more force on the shelf to pull it away from the bottom of the glass area?
Thx.
Nope. The back edge of the panel is just kinda pinched between the rear window area and the roof of the engine compartment. If you have speakers on your rear deck, they may be hindering your removal effort.
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Old 09-20-2020, 09:48 AM
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Thank you Kev, a good tug was all that was needed.
Old 09-20-2020, 02:10 PM
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" I also put one inch closed cell foam over the engine shelf behind the seats. "

Kurt, I'm wondering if you added the one inch closed cell foam over the foam that is originally in place or under it. If under it, did you have problems lifting the original foam.
At the moment I have all of the original foam lifted except and the very top of the shelf where it appears to be well glued to the shelf and I'm afraid to go further for fear of ripping everything to shreds, So it looks as though I may have to add extra sound deadening over what's already in place which would not be my prefered method of doing things.
It all seems like a lot of effort for very little gains, but I've started now so I'll continue.
And BTW in my case, there is no padding at all under the floormats so anything that I add will be a plus. The sound deadening that I've purchased is quite thin so I may not notice any gains at all. We shall see.
Thx
hughc

Last edited by hughc; 09-25-2020 at 04:35 AM.. Reason: added quotation marks
Old 09-25-2020, 04:34 AM
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Hugh,

I put the one inch CC foam over the existing material on the rear shelf, not only to avoid the mess but for the additional insulation. That covered the rear shelf and back wall (behind the seats). I believe I put an 1/8" layer of MLV over that as well. I also removed the rear speakers as the door speakers were enough for me. Not sure how much of difference that made.

On the floors I put closed cell foam, I think it was either 1/4" or 1/2" that had an 1/8" MLV backing and then the carpet over that. This did cut down on road noise. I would recommend new, stock engine mounts (if yours are original you ought to anyway) and a new window seal, too.

You may want to think about a small layer over the tunnel - behind the seat belts to the area below the rear seats (covering the trans coupler access). I haven't done that yet but a fair amount of trans noise comes through there.

There's even more you can do. The improvements are small but together they make a noticeable difference. My 993 has a ton of factory insulation so done correctly it will make a difference. As I said they will never be Lexus quiet but I've also seen some guys sell these cars because they were too crude and wanted something more modern. I'd rather keep it and make my own improvements like Porsche did with the 964/993 in civility.

When I just started driving back in the '80s I was talking with a Porsche mechanic (his name was Fritz, thick German accent, believe it or not). He tried to talk me out of my desire to own a 911. He said they were noisy, cramped, etc - SCs and Carreras were virtually new at the time. Didn't care, I still wanted one. Now that I'm older I see what he was trying to say but there really is no alternative to these cars anymore. I'd rather make the extra effort and keep the car.

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Last edited by KNS; 09-25-2020 at 06:54 AM..
Old 09-25-2020, 06:50 AM
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