Morten U need a filter that can flow a ton of air. Your question is somewhat subjective, but It sounds like a large rectangular filter with a custom made polycarbonate top and bottom my be he ticket.
Take a look at the size of this sprint car filter (
Racing Filters - Home).
Do not use these if u want performance (
Hilborn Fuel Injectors) This bootie filter will takeaway a lot of horsepower.
ITG makes some excellent filters (but its going to cost U) They will flow a bunch (do not use K&N
oil on their filter!!)
Some more info for U to consider. Tall Ram tubes = more low end TQ, Short Ram tubes = More upper end Horsepower
The shape of the Ram tube top is important ( can be worth up to 10% more power).
Hope this helps
Mark
Hope this helps