How much horsepower does a 1955 Shelby Cobra have?

There's no such thing as a 1955 Shelby Cobra. Carroll Shelby's Cobra project didn't begin until 1961. The cars used AC Ace chassis and were fitted with Ford V8 engines. The horsepower varied depending on the engine used, but generally ranged from around 260 hp to over 400 hp in later, more highly tuned versions.