If the air filter isn't the bottleneck, then a less restrictive filter won't do much good. Eyeballing the WBX intake tract makes me think the throttle body is the choke point.

Raymond

Sent from my iPhone

> On Mar 29, 2015, at 9:25 AM, Loren Busch <starwagen@GMAIL.COM> wrote:
> 
> ​RE: K&N Filter in a WBX
> 
> When I first got my '90 Westy I picked up a K&N filter.  On my first long
> trip I kept careful numbers on gas mileage.  at the midpoint of the trip,
> at about 1,300 miles, I swapped in the K&N.  When I got home I compared
> numbers, fresh stock air filter on the first half of the trip vs. the K&N.
> And not a whit of difference that I could see.  I used the K&N for several
> years but got lazy and went back to stock filters, don't have to clean and
> oil them.  As Dennis said there have been various reports over time that
> the K&N does not really do that good a job as an air filter.