I scraped off the floor sound insulation looking for more rust. It’s not too bad. My question, what are people doing to replace it? Is there something that replicates this material? Apologies, I’m sure this is covered already somewhere but I don’t have much luck with the search tool

First Auto Atlanta sells a “tar” kit. While relatively simple to install you will probably get a variety of opinions as it tends to trap moisture once it comes in.
Personally have done it a couple of different ways. For me you should paint the metal before installing. The main problem is that getting the tar to adhere to “valleys” in floor pan.
I am just starting the ball rolling with the where to buy it. Your final decision should incorporate others experience as most will have more expertise than I.

The original tar was good for a cheap 1960’s product. I would never use it now.
Look at lizard skin. My old shop uses it on their $200-350k builds and they are very happy with the product.

Upol tiltable truck bedliner works well too.

NVH treatments have come a long way. The industry still uses bake on mastic patches and/or Liquid Applied Sound Deadner (LASD) via robotics.

Constrained layer damping like Dynamat will be the most effective at reducing noise. Especially for the low frequency structural noise that will originate from the vibration of the 914 floor pan.

The downside for OEM's is that constrained layer damping is heavier (negative for fuel economy) and more expensive than spot applied LASD. Constrained layer usage is strategic. Usually used were LASD isn't enough, or cannot be applied easily by robotics.

Other Liquid Applied Sound Barrier (LASB) products are typically only effective for high frequency airborne noise sources. Products like Lizzard Skin, or bed liner sprays will help, but won't be as effective as constrained layer products. LASB's are lighter than constrained layer products and will offer some noise reduction for higher frequency airborne noise that would tend to reflect off a bare metal surface. LASB's won't do anything for low frequency structural borne noise.

Everything in life is a trade-off. Only you can decide but there are better options than the OEM tar/mastic which was prone to holding moisture under it.

Short background on NVH:
https://insights.basf.com/home/article/read...nd-lasb-systems

Agree with the others! I just primered it, sealed it, painted it, and then put down Kilmat sound deadener.
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Dynamat over new paint.

Found a photo of the Kilmat installed. I later took the left-over Kilmat squares/pieces and installed them into the doors. And, yes.... I DID install my vinyl roof prior to painting the exterior of my car. Don't do this!! It worked out but what a PIA! Lessons learned!!

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@friethmiller : For the areas where the carpet is usually bonded to the interior, how did it go on the stick on sound deadening mat (inner long areas for example)? Same as if it was metal surface?
Thanks!

I believe I used 3M spray adhesive on both the mat and the carpet. No issues at all with adhesion. The problem I have right now is that my passenger side floor mat slides on the Kilmat since it's not glued down. I'm planning on using some carpet tape once I get in there to wire in my A/C Evaporator. It's on my short list.

Spray glue - same as you would use to the sheet metal.

Constrained layer damping is butyl on bottom with thin aluminum top layer.

The butyl acts a a decoupler and mass damping absorbing energy. The top aluminum later add a constraint that helps limit the motion of the butyl increasing effectiveness vs. just a layer of raw butyl. The aluminum top layer won't come loose from the butyl.

What is the name of the seam sealer that you used?

I also used UPOL, they are the suppliers to Wurth. That fact it can be tinted is great for custom jobs. I would still put down some Lizard skin for more sound cushion. I plan to do this with my next two builds. Orange 914/flairs and 2.2ES6 plus a 64 356 outlaw.

Matt

Upol gets my business here. Even comes with it's own applicator.

Thanks for the explanation ,I used a generic butyl that I bought on a country wide auction site,happy with it because Dynamat is mental money in my country besides.
Lined the floor and used 75mm wide offcuts strips inside the doors ,made a pretty good difference so was happy,also lined the backpad with under hood sound matt but @ the end of the day well worth it but the six is bloody loud really .

Much like the OP, I scraped all of the 1970 sound deadener from the car (massive PITA), I primered the floor, and put down Noico 80 mil sound mats, in the doors also. I think they have butyl in them, I brushed on Second Skin Spectrum to the firewalls, and any spots I missed. I am also going to shoot everything with bedliner, both under and in the interior. That should be fairly quiet. Especially with an electric motor.

Car has zero rust, BTW. Function of sitting for 38 years on jack stands in Arizona.

we have the factory duplicate kit on the shelf. We at one time had these factory insulating tar new in factory original parts bags. They were dried out but still perfect templates to make new ones, so we did. Same material exact pattern, work GREAT stick heat beat and paint just like the factory did