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that self made thingi looks decent and I guess it could work, what I always wonder is what happens when you are driving 120mph and air actually gets pushed in so to say. how does that affect the need of change of timing and fuelling ?
Back in the day 'ram air' was all the rage. However, even at 120 MPH the air pressure will be minimal (tests have been done - like 1/2 PSI, nothing like a supercharger). The big advantage of 'ram air' was really cold air (but 'ram air' sounded better to the marketing guys and gearheads). The carb (or EFI) would accomodate any additional air pressure you're likely to see (unless the jets are borderline, in which case it might be a little lean), though if it really developed some 'boost' (like a whole pound!) the timing might need to be retarded slightly to avoid detonation.
My big concern is water coming in when it rains. I cut a hole in the bottom of the battery shelf and built a 'dam' around it on the bottom (in the fenderwell) to keep as much water and junk out as possible, and avoid driving in the rain if possible. Water probably wouldn't be too much of a problem with a carb, except for a soaked air filter, but MAF meters on EFI don't like it since it cools the sensor making it think more air is passing through.
The biggest mod I had to make what to the air cleaner so it would have a 4 inch inlet. I rolled a piece of flat sheet metal with a lip on the end to 4 inches, fit it to the air cleaner and then welded it. The tubing is just 2-45 degree 4 inch elbows I found on the internet coupled with 4 inch silicon rubber connectors with clamps.