MEGABOMB HEADER: The science behind the MegaBomb header may be FMF's greatest engineering accomplishment to date. You can bolt on a Megabomb with an existing FMF Racing muffler for as much as a 3hp boost, plus the Megabomb actually reduces noises levels by as much as 1.5dB. The Megabomb technology is revolved to produce more low end to mid range gains as well as broadening out the mid to top end power gains over stock. The Megabomb is best used for Motocross/Supercross and GNCC style trails. Used by Factory Teams, the Megabomb is the next level technology you can have today. Produces long header torque and short header over-rev Reduces sound output as much as 1.5dB Increases output from stock motor as much as 3hp Made from premium American TiMetal material This is used for a single sided exhaust system except part # 014553 Fits: BETA RR350 4T EFI 2020-2021 RR350 Racing 4T 2020-2021 RR390 4T EFI 2020-2021 RR390 RACING 4T EFI 2021 Beta RR 4T 350 2023 RR 4T 390 2023 RR 4T 480 2023