* Six-cylinder: The base engine was a 170 cubic inch inline-six, producing around 101 horsepower.
* V8 options: Several V8 options were available, with horsepower ranging from approximately 164 hp (289) to 271 hp (289 High-Performance) and even more with the optional 427. The specific horsepower depended on the carburetor and other performance features.
Therefore, there's no single answer. You need to specify which engine was in the particular 1965 Mustang.