OK, had the Terraclean done.

Firstly, the guy at Queenshill Garage, Newport, Gwent was great. Explained the process and was very enthusiastic about the whole thing.

Started engine, put my hand on exhaust outlet and told me to 'sniff' and smell the fuel. An hour and half later I returned in time for him to fire up the engine - and an atom bomb like cloud of black soot came out of both exhausts ! Then a quick sniff of the fumes - Clean !

At first, couldn't tell any difference in performance, but after a while, it's the little things you notice. Not have to touch the accelerator pedal too much on take off, smoother acceleration and smoother sounding engine. Not tested the MPG yet, but since there's less un-burnt fuel coming out of the exhausts, I'll assume it'll be an improvement. Very recommended procedure to get done. And certainly recommend this garage if you live near Newport  RR Sport Supercharged Vesuvius Orange 4.2 V8 First edition

Prefer RR Vouge S/C but they don't do Orange !

how much did it set you back? im sometimes in bristol and newport is only a short way from there. cheers ! Recently bought a 2007 RRS HSE TDV6 for a Pimp-My-Ride-Project.
DONE: Meduza front bumper, AB rear bumper, AB tailpipes, calipers repainted, rear upper tailgate upgrade, side steps, AB front grille, AB side vents, rear LED lights, clear side repeaters, integrated daytime running lights, LED headlights.
TO DO: color code sills and pillars.

£110 + VAT for 4.2 L , usually less for smaller engines, but not much. Mobile mechanics are offering it for £108 on ebay  RR Sport Supercharged Vesuvius Orange 4.2 V8 First edition

Prefer RR Vouge S/C but they don't do Orange !

i've read some good stuff about the procedure since your post. going to book it in next time im near bristol in the new year. thanks ! Recently bought a 2007 RRS HSE TDV6 for a Pimp-My-Ride-Project.
DONE: Meduza front bumper, AB rear bumper, AB tailpipes, calipers repainted, rear upper tailgate upgrade, side steps, AB front grille, AB side vents, rear LED lights, clear side repeaters, integrated daytime running lights, LED headlights.
TO DO: color code sills and pillars.

yeah, I've only ever heard good things said about it too  RR Sport Supercharged Vesuvius Orange 4.2 V8 First edition

Prefer RR Vouge S/C but they don't do Orange !

How you getting on with it a few hours after ? any noticeable difference in mpg ?
ive just enquired about getting this done to my SC

not really been anywhere in it yet, except to take it back to LR to refit air compressor under warranty. If you see how much carbon soot comes out of exhausts, you'd well believe that its worth it ! Lol I had to wash car when it came back as it was covered in a thin film of soot all over !  RR Sport Supercharged Vesuvius Orange 4.2 V8 First edition

Prefer RR Vouge S/C but they don't do Orange !

Did you have to change the oil after? 91 BMW 850CSI

they didn't do that, as its the fuel system thats cleaned, not the oil

They disconnect the fuel line and attach the machine which pumps chemicals into the fuel system which in turn cleans the carbon from wherever fuel has previously been - injectors etc  RR Sport Supercharged Vesuvius Orange 4.2 V8 First edition

Prefer RR Vouge S/C but they don't do Orange !

Sweet. Will have to do this on my V12 91 BMW 850CSI

I had my TDV8 done a couple of months ago, its a little smoother and "nippier" but I've seen no increase in mpg.
The chap who carried out the terraclean said he'd done a TDV8 full fat a few weeks earlier and the owner said he'd been getting an extra 3 mpg. To be honest I was a little dissapointed
He did also say they get different results depending on the type of driving the car has done in the past.
Those that spend a lot of time on the motorway don't tend to notice as bigger difference as those who spend most of their time tootling round time, which makes sense.

According to the onboard trip its averaging 13.8mpg!! But to be fair 90% of its use is when the wife does the school run which is only a couple of miles thru a small town so very low speeds and engine doesnt even get warm.
I take it to work once a week or so to give her a run out and i'll average 22-24 mpg over a 50 mile trip on a mixture of A and B roads.