Four hundred and one horsepower from a small block Chevy - achieved with a Speedmaster downdraft intake system. The results were captured on the dyno and documented on video by engine builder and tester Richard Holdener.

The Downdraft Approach

Downdraft intake systems take a fundamentally different approach to airflow compared to conventional single-plane or dual-plane manifolds. By feeding air vertically into the engine from above, the system leverages gravity and a shorter, more direct runner path to improve throttle response and volumetric efficiency. The design traces its lineage to European racing applications, adapted here for American V8 platforms.

The Numbers

The Speedmaster downdraft system delivered 401 horsepower on a small block Chevy during dyno testing. That number represents not just peak output but a power curve shaped by consistent airflow distribution across all eight cylinders. The system is designed, engineered, and manufactured in-house by Speedmaster - from the manifold casting to the throttle bodies.

What This Means for Builders

For small block Chevy builders looking for a combination of strong output, distinctive aesthetics, and engineered precision, the downdraft system offers a compelling path. The 401 horsepower figure demonstrates that the system is more than a visual statement - it is a serious induction setup backed by measurable results on the dyno.

Watch the full test above for the complete breakdown of the power figures and the system in action.