The GM exhaust manifold casting number 3797901 identifies the high-performance, 2.5-inch outlet "Ram Horn" style manifolds used on early 1960s Chevrolet 327 small-block V8 engines. They are highly sought after for restoration and high-flow performance builds because they offer significantly better flow than the standard 2-inch versions.
Identification and Side Placement
Casting 3797901 (Left/Driver Side): Used primarily on 1962–1963 Corvettes with 300hp or 340hp engines. It features side-facing mounting holes for generator or alternator brackets.
Used between 1962–1965 on Corvettes and some full-size passenger cars with 327 engines. It is often associated with Fuel Injection (FI) models because it lacks an internal choke tube.
Key Specifications
Outlet Size: 2.5 inches (standard manifolds are typically 2.0 inches).
Material: Cast Iron.
Design: "Ram Horn" style with a side-facing accessory bracket.
Applications:
Corvette: 1962–1965 (High-performance 327 models including 300hp, 340hp, 360hp, 365hp, and 375hp).
Full-Size Chevy: 1957–1970
