Features: The best filter in the world can’t do its job if there are leaks in the seal of the airbox. Twin Air’s PowerFlow Kits ensure a leak-proof, fool-proof fit with a rigid, lightweight aluminum cage that replaces your flimsy, plastic stock cage and, when needed, a billet-aluminum flange that bolts tight to your airbox.. PowerFlow Kits are custom-designed to each unique application for superior airflow, improved sealing surface, removal of the restrictive backfire screen, and ease of service.. All Kits include a BIO Factory Pre-Oiled Air Filter. Replacements are available separately.. 2-stroke kits include a Twin Air filter and a rigid, lightweight, billet aluminum cage that replaces the flimsy plastic stock cage and provides a tight seal to the airbox . 4-stroke kit replaces the air-restricting stock backfire screen with a screen that has a special backfire-resistant layer of foam laminated to the inside . Kit for YZ450F 10-13 also includes a complete airbox that increases the volume of the intake along with wash plug, cage and all mounting hardware.