Maximize your engine performance by monitoring the air-fuel mixture. The closer you come to a perfect mixture, the more power your engine produces, the smoother it runs. The K&N® gauge tells you instantly and accurately if your engine requires a richer or leaner air-fuel mixture. Just weld a mounting nut to your header pipe and monitor your mixture anytime, under and road or track condition. An essential tuning tool for carbureted, early fuel injected, or turbo engines. Note: Only for carsrunning unleaded gas.