Right these are the details of what Im doing if anyone wants a go. Dont blame me if you cant get it to fit though!
Im getting a BMC Carbon Dynamic Airbox - custom version for a BMW 3.0 Z3. It has the full 150mm diameter but only 160mm in length which is just short enough to fit downwards in the gap where the Renault airbox goes. Itll need an 83mm 90 degree elbow of Samco hose cos the throttle body egg-shape would be 83mm diameter as a circle. The outlet from the CDA is 85mm so itll just stretch and fit on.
The inlet side of the CDA at the bottom is 80mm, and the connection from the Renault air feed (coming from the wheelarch) is also roughly 80mm. It should just about hook up, if it doesnt Ill make it fit somehow or replace the hose with the 80mm hose that comes in the kit.
The actual pressurised air feed, which you need to make the CDA work as it should, is no problem cos Ive already got a front facing ramscoop in my bumper anyway, where the foglight used to be.
However if you dont want to mess about like this, then there is a CDA listed in the new BMC catalogue for Clio 1.8 16v >95 which supposedly has an adapted flange. I cant see how they can possible make a standard size CDA fit, and it does say that it is the biggest standard size one. Still, its billed as being for fitment to a Clio 16v, so if it doesnt go on, I cant see why you couldnt just return it.