OK turns out those filters are around 100 bucks each, so so much for a cheap solution.
Here is the final iteration of bellmouth, I am considering another design which is more suited to turbo plenums, where the entry to the trumpet will be flush with the floor of the plenum.
This is the design for NA engines, which I'm calling free air bellmouths
and this is something I'm considering for turbo/sealed plenums (i will only be supplying the trumpets, its up to the builder to build the plenum and weld them in to it)
