Who runs without a filter?

[Dan!]

Personally, make a custom air intake and sack off the standard restrictive pipe. And then use a panel filter in any other cars 'standard' airbox, HDi's are quite bulky but easy enough to source, realistically you could use the airbox of almost ANY car, have a look round and see which ones are a good shape, easy to adapt etc, then just get a good cold air feed to it.