How much horsepower would a cam headers and 4 barrel add to my 1978 305?

Installing a cam, headers, and 4-barrel carburetor on your 1978 305 engine could potentially increase its horsepower by around 30-50 horsepower. However, the actual power gain can vary depending on the specific camshaft, headers, and carburetor you choose, as well as other factors such as engine condition, tune, and exhaust system.

Here's a general breakdown of the power gains you can expect from each modification:

Camshaft: A performance camshaft can alter the timing and duration of the valve openings, allowing more air and fuel to enter and exit the cylinders. In general, a camshaft designed for performance can add 15-25 horsepower to your 305 engine.

Headers: Headers are designed to improve exhaust flow by reducing restrictions and allowing the engine to breathe more efficiently. Headers typically yield a power increase of around 10-15 horsepower.

4-barrel carburetor: Replacing the stock carburetor with a 4-barrel carburetor can increase airflow into the engine, leading to a power gain of approximately 10-20 horsepower.

It's worth noting that these are ballpark figures, and the actual power gains may vary depending on your specific engine and modifications. Additionally, it's important to ensure that all the components work together properly and that the engine is properly tuned to maximize the benefits of these modifications.