The horsepower of a 1986 Chevy 454 truck engine varied depending on the specific application and configuration. There wasn't a single horsepower rating. You'll find different horsepower figures depending on the source and whether it's the gross or net horsepower rating.
Generally, you'll see figures ranging from 230 to 270 horsepower. To get a precise figure, you need to know the specific engine code (found on the engine itself) and consult a factory service manual or other reliable resource for that specific engine code.
