Tech tip: OEM sound deadening

richiep

Club Member
Thought I’d spin this topic off from the Project Dixie thread as it is useful info for all that should maybe get a sticky somewhere. Sound deadening during restoration of an S30 is an issue that often leads to people trying all sorts of different solutions, especially if the original factory tar material has been removed during the tear-down and bodywork phase. Often this is because it has dried out, become brittle, and/or lifted and let moisture in, contributing to rusted floors, etc. (at the factory, these tar mats were applied directly to the bare metal and then overpainted - no primer or paint underneath!).

Many people end up using a modern product of the Dynamat variety - bitumen-based, with shiny foil skin, etc. While that looks very “Discovery car show style” and certainly does the job, it is unsatisfactory IMO if seeking to replicate the factory look. Finding alternative products is difficult as if you try searching the web, mostly you are confronted with pages of silver shiny Dynamat knock-offs with extravagant marketing claims.

HOWEVER:
Nissan still produce and use a version of the original bitumen sound deadening sheet material. It is used on a variety of modern vehicles, and can be purchased from Nissan directly- although the prices from Nissan U.K. and other U.K. or US dealers are shocking at about 90 quid a sheet.

But - one can purchase them from Japan at a considerable saving - costing about £25 a sheet. I ordered them from Amayama, who have a massive database of Japanese manufacturer parts searchable by part number, with factory manual diagrams to help. With post, it came in about £240 including post, given they are quite heavy and large.

To do a Z in a way that matches the factory design apparently requires five kits. Each of those kits is one adhesive-backed sheet approximately 80 x 100cm. That should provide enough to cut all the sectional designs from. The material is slightly thinner than the 70s stuff but is a part number succession piece, so is “correct”. I will be applying mine over epoxy primer as opposed to bare metal, and then overpainting with more epoxy, 2k primer and base/clear. Application will be with a heat gun to warm up and a roller.

The all important info:
G5930-89904 “Insulator”
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I also managed to track down some designs someone had created in CAD for the floor sections for a 240Z. Still hunting for info on the tunnel but there are reference images out there. I will update this thread with that stuff. Here’s a snap of the templates though:
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uk66fastback

Club Member
Fantastic work richie and well worth a sticky. My floors had localised holes due to the damn original stuff lifting and letting moisture in. The rest of the floors were fine. If this had been a year or two ago I might have replaced the lot with this.
 

richiep

Club Member
Would be nice to get those templates printed in 1:1 size for tracing.

Great find tthough!
Yeah, indeed! The home printer was a bit of an impediment though!

I am using the measurements however to scale up on some masking paper (just got a huge roll) so will make paper versions first before transferring onto the tar mat.
 
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toopy

Club Member
With the metal epoxy coated rust shouldn't be an issue in the future, but using basically the same thing as was used originally, isn't it just going to go brittle over the next 15 - 20 years? It might not rust as before, but the sound deadening properties will be reduced i would of thought. Obviously that's quite a time scale, but we are doing all this restoration malarky for longevity and continued use of said vehicle.
 

Mr.G

Club Member
Looks good and I agree can't stand the shiny stuff that is so apparent everywhere but I would prefer if they went butyl based rather then bitumen. It's the bitumen stuff that cracks, lifts up and allows water to get underneath. Dynamat is butyl based not bitumen.
 

richiep

Club Member
With the metal epoxy coated rust shouldn't be an issue in the future, but using basically the same thing as was used originally, isn't it just going to go brittle over the next 15 - 20 years? It might not rust as before, but the sound deadening properties will be reduced i would of thought. Obviously that's quite a time scale, but we are doing all this restoration malarky for longevity and continued use of said vehicle.

Does it go brittle in all the cars made over the last 15-20 years that have used it and still use it? Like I said, this is still used in current production Nissans. The same question could be asked for all those flashy Dynamat type things - they are all bitumen based. Do they dry out and crack up? There's also the fact that environmental conditions play a major role in the brittle state of the stuff in the older cars. Most of them where it has cracked up are dry state US imports, where they experienced temps of 80-100+ F year in, year out for decades. I'd wager restored UK garage queens aren't going to experience that kind of punishment. Other UK cars where it ends up needing removal are due to rust either caused from damp carpets starting at the edges and getting underneath the mat or rust eating the way in from the outside. That's going to be the same with any material. It in fact makes me shiver to see interiors completely plastered in Dynamat because you've got zero hope of seeing any problems from above if moisture does get in.
 

tyroguru

Club Member
Genuine question as I have no idea about these products: how much better at sound deadening is a modern product such as Dynamat than this product? For those of us that aren't too fussed about replicating the factory look especially in areas that can't be seen, how big is the difference?
 

richiep

Club Member
No idea. All the manufacturers make claim and counter claim about efficiency, value, etc. TBH, under normal conditions, I bet there’s little in it. A few dB points? In the end, if you aren’t looking for OEM quality and appearance, it’s about weight, claimed efficiency, and above all price.

For me, I wanted a solution that would provide an OEM correct look; although Dixie will be a resto-mod in some respect, it will be a period correct one cosmetically. Also, the above info is useful to those doing a stock restoration and looking for accuracy, because that will increasingly matter as values continue to rise.
 

TimFZ

Club Member
Panel damping pads (unconstrained layer damping) is generally better the softer the material, so inevitably with time, the hardening of Bitumen materials will lead to a loss of performance. Thickness should be 1.5 to 2x the panel thickness as a minimum.

When I apply this material industrially, to get the best effect with about 80% of the panel surface being covered. We do this as there is no time for R&D testing and we need a quick solution. It should reduce noise emissions by well over 10 dB(A) with the greatest effect from the 1kHz band and upwards. It will have little effect at low frequencies but the added mass can be used to tune out certain panel resonances at the factory.

For the automotive world, there is the time and budget for R&D testing so many hours are spend reducing the amount required and optimising the location to reduce cost and weight. That's why sometimes they are added at jaunty angles as this was found to be the best compromise for resonance control and noise reduction.

If you use a modern material like dynomat and fit it across the original location and use slightly more than factory you should get adequate performance with little compromise. With slightly thinner materials, increase the area slightly in non visible areas.

A good bond is required but never use a fully hardening adhesive or the effect will be reduced.

If the materials were originally porous, why on earth did they not stick them to a primed surface? Probably a better bond was found on bare metal than on the paint.
 

richiep

Club Member
Update: I’m working on the full size templates in paper from the A4 size print outs. Unfortunately, the one with all four pieces on it is illegible- resolution isn’t good enough on the text at any size - but I’ve worked from the other sheet of the under-seat ones, and then worked out scales, scaled up, etc. A few tweaks needed but when finalised, I’ll share all the sizing info.
 

IbanezDan51

Well-Known Forum User
Unfortunately now the shipping costs have gone up on this…
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However I have found this which looks very similar though the sheets are unfortunately smaller


Did your estimate of 5 include the boot floor Richie?
 

richiep

Club Member
Unfortunately now the shipping costs have gone up on this…
View attachment 57310

However I have found this which looks very similar though the sheets are unfortunately smaller


Did your estimate of 5 include the boot floor Richie?
Yes, although I can have a check and see how much excess I still have.

I had seen those sheets from heritage parts myself actually. Certainly worth checking out, although a little more piecing together needed.
 

IbanezDan51

Well-Known Forum User
They’re 2mm thick… not sure how this compares to yours?

I did an order, plus extra. So should have enough.

I’ll report back with pictures..! Did you ever sort the template out? Would be handy!
 

IbanezDan51

Well-Known Forum User
I’ve got the rough paper ones in the garage but never got around to finalising “clean” versions so to speak. I’ll take a fresh look at them though, see what I can share.
If you want to just drop me a pm with the rough ones I’ll copy them?. Going to get my deadening fitted this weekend. If that’s ok..!

Thanks
 

richiep

Club Member
If you want to just drop me a pm with the rough ones I’ll copy them?. Going to get my deadening fitted this weekend. If that’s ok..!

Thanks
I’ll see what I can do today Dan. I’ve got a bit running about to do family-wise and prep for Japfest on the Z, but I’ll find the paper templates and mark them up with measurements and take pics. Will send them over. I’d recommend making paper first, make tweaks as required, before doing the matting.
 
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