* Year of manufacture: Horsepower ratings changed over the years the 454 was produced.
* Specific application: Was it in a car, truck, boat, or other vehicle? Different applications often had different tuning and thus different power outputs.
* Modifications: Aftermarket modifications (camshaft, carburetor, intake manifold, exhaust system, etc.) can significantly increase or decrease horsepower.
A stock 454 from the muscle car era (late 1960s to early 1970s) might have produced anywhere from 250 to 450 horsepower, depending on the specific model and year. Later versions, or those with stricter emissions regulations, produced less. Highly modified 454s can easily exceed 500, 600, or even more horsepower.
To know the horsepower of a *specific* 454, you need to know its year, application, and any modifications it's received.
