One of the final stages of the conversion was to sort out a new filter arrangement. I had decided to go for the longer trumpet option for the TB's as they give better torque and a little better derivability. They did, however, mean that I couldn't use my old filters.
I got as far as buying a Pipercross filter, but upon inspection I couldn't make it fit without cutting lugs away from it, which I didn't fancy. My attention then turned to ITG who had been recommended.
I contacted a very helpful guy, Andy Jackson, at ITG and explained my problem. He suggested that I took some measurements, and maybe some pictures and send them to him and he would work out what could be done. I took some pictures and then used a gfx program to add the dimensions to the pictures, to help make it clear. I got a swift reply to say that a non-standard JC71 filter could be made to fit, although it would still be a tight fit. The main problem was the large radius on the ends of the trumpets, and how close there were to the front edge of the bonnet.

After a short delay waiting for the filter material, a nice custom filter arrived and I was able to start offering it up to the car. This first involved making a cardboard template of the backplate and then moving it around so that the filter fitted and the bonnet would go on. This was simply trial and error - lots of the latter!
Eventually I had an outline which worked. The problem had been that the way the filter attaches (and where it is better suited than the Pipercross) is that it has a folded return along one edge, which tucks over the backplate and then it is pushed back flat and three clips hold it tightly in place. However, you have to have the space under the filter to be able to get the folded edge over the backplate - it was a compromise of getting enough space and not having the filter sitting too high. Of course, if you offset the backplate too far, the large diameter of the trumpet end would clash with the internal metal mesh of the filter... all good fun!

Eventually it was made to fit and the supplied backplate could be cut to match the template. The cut-out in the bonnet then had to be opened out to allow it to poke through. I used some 'SVA' rubber trim from Caterham to edge my work and give it a nice finish.

 

 
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