As far as your air filter goes I currently am attending UTI a tech school we have several hot rod course that are endorsed by HOT ROD magazine, and HOT ROD TV. they have us experiment with various intakes, and such, and have found that at least on any standard engine a K&N filter does nothing for horsepower, in fact on most applications it takes horsepower away. you might feel a better response but most of the time that is due to the fact that you have anew filter or you cleaned out your airbox when playing with your K&N. I howevere do use a K&N simply because as of right now my 83 is having all sorts of issues and being able to clean my filter rather than buying a new one is saving my tons of money.

NOw then its possible that on a rotary the filter will actually make a difference, but if you look at K&N adds, or any of those adds you'll notice that the horse power gains were experienced with other mods being done as well. If you put more air in, but your engine can;t use it it will screw with your mixture. Most cars are engineered to b the best with thier stock airboxes if you're using the stock intake.

If you change other things. then K&N will probably work better, but if you're leaving your intake don't bother unless you need to be able to clean it. wait until you do some more stuff, and make the changes all together.