* Year of manufacture: Horsepower ratings changed over the years the engine was produced.
* Modifications: Aftermarket parts, tuning, and engine rebuilds drastically alter horsepower. A stock 400 will have significantly less horsepower than a modified one.
* Application: The intended use (e.g., passenger car, truck, performance vehicle) impacted the factory tune and resulting power output.
Therefore, you'll need to specify the year and condition (stock or modified) of the particular 400 small-block to get a more accurate horsepower estimate. A stock small-block 400 might range from roughly 200 to 300 horsepower depending on the specifics, but heavily modified versions can easily produce far more.
