Is it the sticker on the air cleaner????

In 1958, Ford introduced its FE big block, in 332 and 352 inch versions. The top of the line "police interceptor" 352 was rated at 300 horsepower. Hot Rod Magazine tested one and wondered what happened to the power it was supposed to have, as it felt slower than a 57 312. So they put a "300 hp" 352 on Edelbrock's engine dyno (not chassis dyno). Made 200 hp. Performance motor?