The Uni Filter Screen has bigger holes than the stock filter screen so you are getting more air. Not too much more to have to do a mod to the engine. The Pre Filter did not fit over the filter because it was to small. I covered the opening to keep rocks, leaves, dirt, dust, water out of the air box.
I did not want to cut an opening in the top because I feel that the flat way would fill up with stuff and cut my air flow down.
My quad ran great with out any adjustments. I could not tell if it went faster.