Maximum filter area is the first thing you want, like 14" diameter by 3 or 4 inches tall. Secondly, you want cold air to it. You can use your hood scoop and glue some firm blocks of foam to the bottom of the hood that would come down and seal off the bottom plate of the filter if you made the plate large enough. Or, you could run a couple of 4" tubes to atmosphere and funnel the air to a closed filter case.
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