I've read a bit about sound deadening and one technique is to fill hollow spaces with expanding foam to kill resonance. I was thinking of doing this to my roll bar top and maybe the sides. Knocking on the top shows how high of resonance it has. I was think that if I drilled some hols 8-10 inches apart on the underside of the roll bar and sprayed in the foam I could kill the resonance and just fill in the holes. I'm not sure I could weld them since the foam is in there, but maybe solder or lead them in, or maybe just bondo?

What's your reaction to this? Good or bad idea?

the factory already set the car up for this. they all come with holes in the right places

jeff bowlsby has a picture/diagram on his web-site that shows the location of all the factory holes meant to be used to foam out the hollow spaces.
get in touch with him if you can't find the pic on his site.

the german word is "Hohlraumversiegelung" ...

the targa bar has 3(?) holes on each side, often also (wrongfully) refered to as the mounting holes for a ski rack.
there is a aftermarket ski-rack that uses those holes to mount on,
but they were originally used to get the foam in for the hohlraumversiegelung ...

later,
Andy

How about a brand recommendation? Or at least things I should look for in an expanding foam? Thanks.

You are kidding right?

Look what the factory installed foam already caused us (rust wise) and now you are planning to add to that?

And no, after you've inserted the foam, you can no longer weld (the foam will burn and melt)

Finally, I think you will achieve very little from this. Face it, a teener is a noisy car

cheers,

Jeroen

HiLow Mark,

in my opinion this is a very very bad idea !!!
It took me 4 days to get rid of all the foam the factory put in my car and i found lots of surface rust behind that foam.
Andy, this is not that kind of "hohlraumversiegelung" that i have in mind. I'm using wax based products for rust prevention.
Jeroen, you're absolutely right; a 914 owner has to live with the fact that this car is noisy, especially when the roof is open

Benno

Also, please keep in mind that IF you do use foam to fill up these cavities, that this foam expands.

If you apply it wrongfully, the force of the foam-expansion may warp and disfigure the surrounding sheetmetal.

So, if you decide to go the foam-route, be very carefull!

cheers,

Jeroen

Jeroen is right about the expansion and I have to say here that it may not be very wise to use any spray-foam or other 1 component foam. The volume of the targa bar is so big and there are too few and too small holes to outside, that it will take a long time until the foam is cured. I think you should use 2 component foam that cured chemically, not by air-drieing.

foam holds moisture which equals rust.

please, please, please save the next owner the rust repair!!

I'm going to play the devil's advocate here and say that no, a 914 owner doesn't have to live with anything. To each his own and cheers to the inovators.

"Can't turbo a 914" - disproven
"A 914 will never shift as well as a modern car" - disproven
"Carbs are cheaper than PEFI" - disproven
"914's are all noisy. Live with it." - jury still out

-Ben M.

first of all, he's in california. and we all know "it never rains in california ..."

second, he wants it for sound-proofing, not rust prevention.
how often do you see a rusted targa bar? even on the east-coast? or in canada? or in germany?

if he thinks it might help him to get the noise down, i'd say go for it.
but i am actually very skeptical that it will help, noise-wise ...

if you're talking rust-prevention, the foam is a very very bad idea.
it works good for about a year or two, by then the foam is saturated with moisture and we all know the rest of that story.

Andy

haha, very funny ... believe or not, I spend the last week in Los Angeles and it rained on two days ...

but i think most of the time you're right about the weather in socal

benno

and you didn't have time to come up to the bay area and hang out with us?
shame on you!

Andy