Pulleys

Just a quick question. I was wondering how much rear horsepower would be expected from pulleys for an 89 mustang gt. They're mac pulleys. im just curious, they rated at 12-15 hp, but im guessing that's in the engine and not rear horsepower. If anyone knows that would be great, just kinda curious. thanks

I'd give it 5 RWHP on a good day.