As part of my recent major overhaul of the rear end of the 390 I removed the exhaust system from the manifolds backwards. Apart from the fabricated manifolds which are mild steel (with short stainless sections welded on for the flared joints) it's all stainless steel, though you wouldn't think so from this photo:
It cleaned-up well enough with a stripping disc in the air drill:
Although I haven't been able to find a reference to it in the extensive history file that came with the car, I know this exhaust has been on the car for at least 15 years (as I bought it in 2000!). It's never been particularly quiet in the time I've had it, not that that is necessarily a bad thing ;o) but I did read somewhere that future MOT requirements will address exhaust noise issues and I thought it would be better to do something about it now rather than wait till an MOT failure slip appears.
My understanding is that exhaust systems are typically packed with wire wool and - effectively - Rockwool loft insulation! The TVR system is a single-silencer arrangement: the two inlet manifolds feed into a combined plenum chamber, the output of which is passed through a large-bore perforated tube and exits directly to the tailpipe, shown here by marker pen lines (gas flow right to left):
My understanding is that the corrosive exhaust gas destroys the wire wool which then gets blown out with the tailpipe gases. I decided to cut the silencer open and repack it, this time with stainless wire wool!
Of course I proceeded to cut a rather smaller access hole with the plasma than maybe I should have (note MDF cutting template!):
The chamber surrounding the perforated pipe contains the wire wool and Rockwool. Or it would, if years of corrosive gasses blowing through it hadn't eroded it; this is about all that was left:
The wire wool comes in half-kilo packs that, unravelled, measure about 19m long and about a hand's width. I bought two packs as I wasn't sure how far the stuff would go:
Installing a kilo of wire wool turned rapidly from precision surgery into determined stuffing, using a length of snapped broom handle as a ramrod:
There was a little bit left that I just couldn't squeeze in!
The double-skinned silencer was then rewelded (not the tidiest welding I've ever done, I think all the soot in the silencer was contaminating the weld):
and with the other sections of the exhaust cleaned back to shiny stainless, it was set aside to await refitting to the car.