Performance Package improves usable air filter exposure area by 20%.Walker's line of high performance air filters are now available for your Volvo Marine diesel inboard engine. These Walker Flat filters perform much better than the stock paper filter, and resists water, moisture, and blowby gases, so you get high air flow, and High-Air Performance when you need it.Kit for Volvo D4 and D6 engines includes High Gloss Black metal air filter cover and high-performance, high-flow, air filter.The kit for the D9 engine includes two high-flow filters, adapter rings and an air filter cleaning kit. The washable air filter elements in both kits are designed to deliver high air flow to your engine season after season.