sound padding, again

[gerard vaglio]

In a continuing effort to lighten my 911sc I have been contemplating removing the sound pad/heat shield from under the carpet behind the rear seats.

Since this has been discussed before I’ve done a search on the topic but I’m reading conflicting reports on the effects this will have on interior noise and heat.

Some people have reported that they’ve removed 40 lbs. of material, put the carpet back and have noticed no negative effects. Others say the interior became so hot and noisy they’re going to put the stuff back.

My car is a daily driver and I’d love the benefits of losing 40lbs. in the back but not if it’s going to make driving unpleasant. Can people who know something about this modification give me a little more information. I’d love to try this but don’t want to feel I made a mistake.

Thanks

[turbo6bar]

rdane replaced the original material with dynamat and another product, but there was no weight savings, as I recall. Porsche would not install the original mat if there was no advantage (sound or heat).

Personally, I am going to spray the firewall and underside with Quietcoat. It will be a bit lighter, and it should reduce noise quite a bit. Then, I will remove the stock sound pad and insulation to reduce weight. The main drawback is installation on the firewall will require an engine drop and preclude possible "while I'm in there" tasks. My SC is just too noisy to drive for any stretch longer than say 15 miles. When the engine is off, setting the stereo volume to 16 is really loud. When I'm driving though, volume setting 16 is puny.

I am probably alone in wanting a 911 that is reasonably quiet to permit a conversation. If I want engine and exhaust noises, I will just roll down the window.

Jürgen

[Andras]

gerard,

I have removed the sound blanket, not for weight savings, but because it was dried out and deteriorating. Now my children (very young and small) complian that it gets hot in the rear seats. And the engine noise is much louder without it.

So I plan to replace it once we redo the top end of the engine next month.

By the way, I already have the new one, and it must weigh all of 1 or 2 pounds (1/2 to 1 kg). I doubt that kind of weight saving is worth the lounder and hotter car.

[gerard vaglio]

andras,

Thanks for your reply, when you say you have the new one and it's only a few pounds are you talking about the pad in the engine bay or the interior padding behind the rear seats?

If there is an interior padding solution thats only a few #s I'd love to learn more.

[Andras]

Gerard,

Woops, I was speaking about the engine compartment padding.

But I do know from experience that the padding under the seat back is also quite light (not 40 lbs.).

In the final analysis, you have to decide what is more important to you - relative quiet or the saving of a few pounds.

By the way, when I'm on the track, I remove the seat backs (the seat bottoms are glued in), and I have already removed the heavy York compressor, etc. To my mind, those are much better "removals" than the heat and sound padding behind the seats.

Hope this helps...........Andras

[Frostie]

Just an idea…

What about getting that thermal insulation at the hardware store. Basically it is just 2 sheets of highly reflective material with air-bubbles between. It’s around ¼” thick extremely light and cheap. Then over that use household carpet underlay, this works as an extremely good sound barrier and a moderately good thermal barrier. I can’t see all of this weighing more then a few pounds and would be very cheap.

[rdane]

You'll find the OEM materials very good for their purpose. The problem is not sound but heat. Hard to duplicate the Porsche designs without adding even more weight.

Take everything out and the car will be loud and hot. No way it will make a daily driver for most. I tried my with a exceptional pair of commercial ear muffs


I wouldn't bother to do it again unless I wanted new carpet.

Best weight loss on an SC is half tank of gas and loose the spare tire. After that the back seat up rights. The SC is difficult to drop weight from without spending money.

Sticking to 16" or better yet 15" wheels is a good start at keeping weight down. Loosing the AC and adding fiberglasss bumpers are good fixes. RS door panels only loose the wieght of the door pockets. Just loose the pockets

[Randy Webb]

Someone ought to lay out what exactly _is_ in the rear. I'll start:

For the vertical bulkhead (firewall) starting at the engine, in order there is:
a foam sound pad -- the newer design is much lighter than the old
XX?
paint
undercoating
the metal itself
(items below are inside the interior)
undercoating?
paint
some sort of asphaltic pading
felt
carpet

Is there anything for XX? Did I leave something out? What model years have what items added or deleted from this list? What do we know about the wts. of the various layers?

I think we may be able to improve on what PAG put there originally by using newer technology materials (my car is 30 years old). My expectation is that Quietcoat should be "a lot" lighter and still kill the nose as well as any asphalt based dampening materials. Heat will require a different approach. But I expect we can jointly investigate this and save 20 lbs. or more and still have a streetable car. Of course, there are other wasy to save wt., but I think this is worthwhile.

[turbo6bar]

I believe rdane stated his car is more quiet with the new technology, yet with no weight penalty over stock. If the quietcoat product works as advertised, then it wil save weight. The company is quoting around 40 SF per coat, and I plan to apply 2 coats. I just need to find the time to drop the engine and tranny and clean the entire underside of the car.

This is definitely not an easy project for the weight saved, but it should make the car better all-around for a long time.

One thing I noticed a few weeks ago: I replaced the stock shift coupler with an Apex coupler. I left off the cover to do some test runs. Wow, the noise coming through that tiny compartment was terribly loud. Dunno about you guys, but my cover is just painted metal with carpet glued on top.

Jürgen

[rdane]

I don't know much about the technicalities of sound suppression, just a little. A layer of paint or two (no matter the paint) isn't going to solve the problem in the interior of a 911 imo.

There are newer sound deadening materials that weight less. I might have saved a lb or two but nothing worth the effort of doing the replacement. (I did write it all down some where here) Problem is it takes a combo to get both the sound and the heat down.

The exterior sound mat in the engine compartment is a good place to improve the old technology.

I have yet to see anything new mentioned here on Pelican that will surpass the Dynamat line of products. Love to see something else that is better but so far I am really impressed with what Porsche did 25 years ago.

[Andras]

Woah guys,

The reason that Jurgen noticed more noise when he left off the cover plate has nothing to do with the paint. It was that there is now a direct connection between his interior and the inside of the engine compartment. Sound is transmitted by air to your ears, but also by vibration by sheet metal, thus vibrating the little air molecules, which hit the ear drums, thus causing sound. So what Jurgen was experiencing can be observed also by opening a door just a crack, and no matter how small that crack, you will hear prefectly well what is on the other side of the door. Try it with your TV tonight; TV in one room, you in the other. Then open and close the door, and you'll hear a huge difference.

Anyway, this whole thread is about whether or not gerard is willing to leave off some sound and heat insulation in order to effect some weight reduction.

I hope he has enough information to choose.

Thanks for your patience all...............Andras

[turbo6bar]

http://www.quietcoat.com/html/technology_overview.html

If you go with maximum coverage for a car the size of the 911, they recommend 5 gallons. Dried weight of this product is ~10lbs/gallon, but we are also talking about a lot of coverage per gallon.

I really have high hopes for this "new" technology. I won 40 square feet of asphalt deadener mats in a drawing, and that stuff is mucho heavy. If the Quietcoat can beat the performance of the mats at less weight, I will consider it a success. Regarding cost-- well, my SC has managed to blow the budget to smithereens, but I don't care. I'm having fun.

I really wish I could convey the noise levels coming through the firewall of my SC. Been trying to find a quality noise meter on Ebay, but no luck so far.

Jürgen

[Randy Webb]

Quiet coat is not a paint (tho it is applied like a paint). It works by transforming the mechanical movement that is a sound wave into another form of energy and dissapating that energy. Check out their web site. I have not tried it (yet) but it looks good. Dynamat and the like (Brown something, etc). work primarily by adding mass to a panel, making the resonant frequency lower and the amplitude less for the same amount of energy. That's why they are so heavy.

Personally, I would settle for an acceptible amount of sound dissapation for much less wt. -- if it's a bit louder than stock that's OK. I don't want to drive inside a resonance chamber tho. Somebody on theis list (JO?) uses noise cancelling or supressing headphones while driving -- not for me. We all have to pick what we want, but there may well be better ways to get there than there were 30 years ago. As an example, consider the floor mats in the new Boxsters -- I weighed them and they are a lot less wt. than the ones in my '75 911, but are the same size.

[l8tapex]

To add my experience, A few months ago I took out my sound pad to save weight but now the engine is a bit too harsh. It's not a good sound. Too much intake noise.

I ordered a new mat from Pelican Parts yesterday and I plan on installing it this weekend.

[rdane]

Here is a good read. Lots of problems suppressing sound in our cars. This one is about boats but gives you a wide range of the problems also encountered in a 911.

http://www.uaf.edu/seagrant/boatkeeper/reducing-sound.pdf

[expat]

If you want others to be travelling in your car - dont remove the sound/heat pad under the rear seats. It will make you car hot and will prevent anyone sitting in the back (if this is what happens from time to tiem in your car.

I will post some comprehensive pictures next week that show what happens when you remove this stuff. I've done it and just replaced it last weekend.

I took pictures including scale weights of carpet, sound pad etc.

My personal opinion is this...

If you are after a 'race look' and are stripping your car seriously for weight reduction and thereby (in most cases) not using it as a daily driver, then removing the pad/seats etc is worthwhile.

If you daily drive your 911 and occasionally (or often) take passengers, then its a waste of time and money.

$ for $, pound for pound, most of us would be better off learning to driver better and shed our own pounds (kgs).

[Randy Webb]

Are there any Gen'l Aviation pilots on this thread?? That would be the place to check and see what they use for sound and heat barriers -- bound to be lightwt.

I guess the old saw (from Colin Campbell?) about always looking to motorcycles for sports car tech is only partly right.

[rdane]

Originally posted by Randy Webb
Are there any Gen'l Aviation pilots on this thread?? That would be the place to check and see what they use for sound and heat barriers -- bound to be lightwt.

The head phones are expensive... more than a set of Bose. Helmet is even more and less comfortable. The leather jacket, if you are lucky was government issue Damn jacket won't fit in my Ricaro though. The nomex driving suit is a lot warmer than the typical nomex flight suit though. And three times as thick.

Without both it is typically real cold and real loud in a comparable performance (Porsche kind of performance) aeroplane.