The OE bulkhead is laminated.
![](./images/smilies/spacer.gif)
Which already helps.
![](./images/smilies/spacer.gif)
There is black
![](./images/smilies/spacer.gif)
fire retarding material sandwiched between each side of the firewall ie in between both sides.
![](./images/smilies/spacer.gif)
On my RS200 replica, I've added 1" thick black fireproof insulation to the sides of the rear bulkhead and all across the inside of the cabin side, then added a further carpeted shield over ply.
![](./images/smilies/spacer.gif)
Sounds a lot of work and it is, but is it worth the effort?
![](./images/smilies/spacer.gif)
The prevention is lost if the windows are open and noise also comes through the rear screen.
![](./images/smilies/spacer.gif)
A cone filter makes a hell of a high pitch screaming noise on boost or a high revs also.
![](./images/smilies/spacer.gif)
If you want a quiet MR2 wrap the std airbox, and run a quiet silencer!
![](./images/smilies/spacer.gif)
Good luck
Mike N