SBC Modified Header Long Primary 3-Step

The SBC Modified Header Long Primary 3-Step from Schoenfeld is a purpose-built exhaust manifold engineered for small block Chevy engines requiring optimized primary tube sizing and enhanced scavenging efficiency. Designed for enthusiasts and mechanics building modified engines where stock headers no longer flow adequately, this pair delivers the stepped primary design that separates cylinders into different tube diameters—1.625, 1.75, and 1.875 inches—to match exhaust velocity across the rpm range. Long-primary geometry extends the primary tubes before merging into the 3-inch collector, improving low-end and mid-range torque while supporting higher rpm power builds.

This header pair is constructed from quality steel with black paint finish, providing durability and heat resistance typical of competition and street performance applications. The stepped primary tube design—rather than a single-diameter approach—allows each cylinder's exhaust pulse to exit into a tube matched to its flow characteristics, reducing backpressure and preventing cylinder-to-cylinder scavenging losses. The 3-inch collector merges all primaries into a single outlet, preparing the exhaust for downstream components like catalytic converters, mufflers, or racing collectors. Gaskets and hardware are included, simplifying installation for builders who have the mechanical knowledge to fit long-tube headers into tight engine bays or chassis.

Small block Chevy engine builders—whether street performers, strip racers, or vintage car restorers—benefit most from this header design when upgrading carbureted or fuel-injected mills beyond stock output. The long primary configuration works particularly well on engines with aggressive cam timing, high compression, or significant displacement increases where factory manifolds create exhaust scavenging bottlenecks. Proper fitment requires engine bay clearance and attention to exhaust system routing; buyers should verify compatibility with their specific chassis and intake manifold setup. At 34.55 lbs per pair and measuring 21 x 10 x 38 inches, these headers demand installation planning in confined spaces, but payoff comes in measurable torque and horsepower gains on a dyno.