How much horse power do headers add on 454?

Headers can add approximately 10 to 20 horsepower to a 454 engine, depending on various factors such as the design of the headers, the engine's overall condition, and supporting modifications like carburetors and exhaust systems. Properly tuned headers improve exhaust flow and reduce back pressure, which enhances engine performance. However, the actual horsepower gain can vary based on the specific setup and tuning of the engine.