Stop Choosing Cams by Advertised Duration

Most people choose camshafts based on advertised duration — and that’s where the confusion starts. In this video, Chris from GSC Power Division and I break down what advertised duration actually means, why it’s misleading when used as a decision tool, and how to properly read a cam card so you can make informed camshaft choices. In this discussion, we cover: What advertised camshaft duration really measures Why advertised duration is not standardized The difference between advertised duration and measured duration Why duration at .040, .050, or 1mm matters more How lift reference changes what duration numbers mean How to read cam cards correctly Why copying someone else’s cam choice is risky This is foundational information for anyone building an engine — import or domestic — and it applies whether you’re naturally aspirated, boosted, street-driven, or race-only. If you’ve ever been confused by cam specs, this video is meant to be a long-term reference you can come back to. If this video helped clarify camshaft specs for you, save it and reference it the next time you’re choosing a cam. More in-depth discussions on valve events, overlap, and cam behavior in specific combinations are coming next.