i don`t understand why so many think ram air is not effective, all normally asperated cars will benefit from a forward facing inlet that creates pressure, on my 75 duster i had a snorkel scoop 6in high and i had 2inlbs pressure at 90mph at manifold when i sealed it to the carb, bren if you have header now your slower performace is most likely jetting, headers will effect your jetting , usually making it leaner, also you have to check pressure at the manifold and make sure it dozen effect your power valve.
