SBC Crate Modified Headers Long Primaries

The Schoenfeld SBC Crate Modified Headers Long Primaries (part number 1101V3CM-3) are purpose-built exhaust headers designed for small-block Chevy engines competing in IMCA Modified racing. These headers feature stepped primary tubes that progress from 1.625 inches to 1.75 inches to 1.875 inches, optimizing scavenging across the RPM range while feeding into a 3-inch collector for smooth velocity transition into the exhaust system. Constructed from steel and finished in durable black paint, this header pair includes gaskets and mounting hardware for a complete bolt-on installation.

The stepped-tube design directly addresses the challenge of managing exhaust gas velocity across wide RPM bands—a critical concern in Modified racing where engines operate under variable load conditions. Smaller primary diameters at the exhaust ports maximize scavenging efficiency at lower RPMs by maintaining higher gas velocity, while the progressive step-up toward the collector prevents excessive backpressure at high RPM. The 3-inch collector diameter provides appropriate sizing for small-block applications, balancing flow capacity with the pressure dynamics required for tuned-length runner performance. Long primary tube lengths support lower-RPM torque development, making these headers suitable for engines expected to operate across a broader throttle range rather than peak-RPM-only scenarios.

IMCA Modified competitors select Schoenfeld headers for their engineering focus on class-legal performance gains and durability under sustained racing conditions. The inclusion of gaskets and hardware eliminates the need for sourcing these separately, streamlining installation and ensuring correct fitment. At 34.35 lbs, the header pair reflects the structural integrity expected in a race-duty component designed to withstand thermal cycling and vibration cycles typical of competition environments. Builders and engine shops working with small-block Chevy platforms for Modified competition rely on headers of this specification to achieve reliable, tuned exhaust characteristics within rulebook constraints.