My experiance with K&N filters on the bikes was far better than with foam type filters, which suffered in the wet soon getting saturated and blocked.adamuk said:K&N filter installed in my van. Made no discernible difference at all I am afraid
K&N filters are pleated so have a much higher surface area than paper or foam filters, this increase in surface area allows more particles to be filtered out before the filter media becomes blocked. A new or newly cleaned K&N should flow more air than a new paper filter but a 10 or 20 thousand mile K&N will flow far more air than a paper filter with the same use.
K&N say a Rover V8 will gain 4 to 20 bhp, that could be depending on state of tune, say between 3% and 10% more power.
The Vito has a better standard induction system than that of a 20 year old Rover, so I doubt you would notice a big gain.
That said after 6 months of use a K&N should flow more air than a paper filter and hence better economy and less black smoke, may even help get past the MOT test.