Banpei's two door panda Trueno from Japan

[Ivan141]

I would expect the stock trunk would have had some sound deadening fitted. Certainly cant hurt to install it afterward. There are many sources of noise in the trunk, think of wheelwells, differential, exhaust. Sound deadening can only help lessen reverberation so dont go crazy with it, its better to add a layer of closed cell foam over some strategically placed deadening mats than to cover everything in butyl.
If you really want to cut some noise out a heavy carpet would be your best bet.
Think of something like mass loaded vinyl, weighs a ton but nothing kills noise better. A heavy carpet would perform a similar task, you could add a layer of acoustic wool underneath.
Another great option is to make sure you close off as many 'leaks' as you can from trunk to cabin. Any holes will conduct sound to the cabin. This also applies to speakers. The membranes hardly hinder noise (especially when off).

[banpei]

(10-14-2026 08:15 PM)Ivan141 Wrote:  I would expect the stock trunk would have had some sound deadening fitted. Certainly cant hurt to install it afterward. There are many sources of noise in the trunk, think of wheelwells, differential, exhaust. Sound deadening can only help lessen reverberation so dont go crazy with it, its better to add a layer of closed cell foam over some strategically placed deadening mats than to cover everything in butyl.
If you really want to cut some noise out a heavy carpet would be your best bet.
Think of something like mass loaded vinyl, weighs a ton but nothing kills noise better. A heavy carpet would perform a similar task, you could add a layer of acoustic wool underneath.
Another great option is to make sure you close off as many 'leaks' as you can from trunk to cabin. Any holes will conduct sound to the cabin. This also applies to speakers. The membranes hardly hinder noise (especially when off).

Thanks! Those are really good tips!

It's indeed mostly resonance of the exhaust that I need to address, and the areas I still need to cover is inside the pocket (or cover the pocket with something) and some more to the back of the trunk on the right side. The spare wheel tub is already filled with a spare, so I don't expect any resonance coming from there. I was also planning to add some sound deadening on the wheel tubs inside the cabin as the insulation was removed for welding and never replaced after that.

There are no obvious holes from the boot to the cabin. The speakers are separate units that sit on the shelf, which means the membranes don't carry any waves from underneath. However, I did replace the parcel last year with some softboard that has some thermal underlayment on it. This is maybe two or three millimetres in thickness and probably won't stop any sound. It might be worth removing the parcel and adding a thin layer of insulating material.

The stock two-door didn't have much sound deadening placed. This is the way the trunk looked when I received the car:

It was covered in a layer of primer, and only above the diff was some sound deadening present. Maybe Toyota was only expecting the diff to be noisy?

This isn't that different from the other two-door GT Apex cars in Japan:

And I remember it wasn't any different for the European AE86 that maybe got the really thin carpet that I have as well.

Speaking about the carpet: the OEM carpet is so thin, it isn't helping much either. I agree that an aftermarket carpet would certainly help. I can try to see if a woollen blanket underneath the OEM carpet also makes a difference.

[Ivan141]

I'm using this stuff as firewall insulation, it would probably work well for the trunk too:
https://www.akoestiekwinkel.nl/isomat-vm...atiematten

That shop also sells a cheaper mass loaded vinyl in case you would just want to add a layer underneath your carpet.

And then there is acoustic cotton wool, which is similar to the stuff OEMs put beneath carpets and above the headliner. Cheap and cheerful:
https://www.akoestiekwinkel.nl/ecocousti...on-vulling

[I am not affiliated with that shop BTW, they just happened to have a lot of useful stuff]