After extensive testing, the AIRSPEED II™ adapter has proven without a doubt to have positive gains and a broader power curve on box stock class clone engines, specifically with top-end "dropoff" common with other adapters.
 
Product Specs:
Airspeed Clone air filter adapter- black
Works with all air filters that have a 2-7/16" inlet.
Bolt Holes: 1/4" (2)
Bolt Spacing: 1-11/16"
1-3/8" in height
Includes bracke