Hersh is right, IDAs are considerably taller than IDFs. The problems are that you cannot adequately use IDAs on a standard height GTD engine set up ( I met Fred from Belgium today in the UK, he has a smashed glass rear window to prove it! ) IDFs have some rather nasty characturistics on a GT40, if run on a more than stock engine, and will have considerable "stand off" (blow back of neat liquid fuel) from the tops of the carbs which can cause fires in the carbs, I have seen lots of IDF sets burning nicely. I did a lot of experimentation with IDFs to try to improve performance and reduce fuel stand off, one of which was reasonably successful. This entailed making extended venturi tubes to reach the same height level as the inlet trumpets, using improved radiused edged trumpets to get a smoother air flow into the carbs. Using mesh covers over the trumpets may look OK and in theory stop any ingress of debris, but the result is a very poor air flow, increased richness which if dialled out by the jets just kills high rev performance. The real answer is to lower the engine and use IDAs, which is what you will find on all UK track use cars running Webers. If you are just a road cruiser with a stock cam and compression, no revs over 5K, then it may work, but not for me ! Frank
