Art from Douglas Motorcycles sent me a prototype K&N air filter to try out in the C5.
Installation was painless, EXCEPT that the inner diameter is currently too small. The bracket raises up from the box and prevents a tight seal. See the second photo. Art suggested pinching the top and bottom to get the left/right side to bulge out and extend beyond the bracket. That didn't quite work in my C5.
K&N will have to get it made to our spec's before many people will buy it. I got out a carving knife and gouged out a slot for the brackets. That was ugly as heck but made for a better seal. It is still not perfect, however.
The OEM filter, even when tightened, was not a perfect fit either. The stock setup of plate and self-locking crown nut is pretty ricky-dink, a general "charming" feature I am still getting used to about this bike.
With temps in the upper 30's, but dry, I rode the C5 for 40 miles, mostly on the viaduct in Seattle south to Burien, about 13 miles out, at speeds above 50mph most of time.
With the upswept muffler I didn't hear any sucking sounds coming from the air filter. That muffler sure sounds sweet.
My seat of the pants dyno observed that there is better throttle response now. The C5 is clearly more willing to accelerate at lower rpms and mostly throughout the range. Heading into the stiff wind at 60mph, the C5 was willing to go faster but was not too much in a hurry to do it.
Back on the city streets I noticed a stronger pull in traffic, and was aware that at 40mph in 5th gear it pulls with more authority than before.
The C5 has 994 miles as of today. I will post more stuff here when I get out again. I'm still thawing from this ride!