a lightning 4# lower does not only give a harley 2# extra, it really adds very close to 4lbs but you would be running 2lbs less than a lightning. the only REAL way to determine how much boost you will be running is using the giant formula where you find the ratio of upper to lower pulley, then multiply it by the rpm of the engine then you have to factor in motor displacement and blower displacement and altitude but for the most part a X# pulley will add Xlbs of boost on harley or lightning, but the lightning will always show 2lbs more boost because of the upper.
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