I bought the FMF Powercore for a 2013 KX450, because of the spark arrestor to be able to ride in the woods, and the price. The Powercore bolted on easily and matched the stock header perfectly. Once fired up, the sound was much quieter. Took to the woods, and difference in power delivery was amazing, the pull just seemed smoother from the bottom to the top. The spark arrestor did not seem to reduce power at all.