This is not the first foray into three-barrel carbs. Holley had a large-cfm three-barrel in the ’60s and ’70s, and we owe “the notch” to it. Edelbrock’s original single four-barrel intake manifold was called the “_4B”: C4B for Chevy four-barrel, F4B for Ford four-barrel. The carb mounting pad was originally a four-hole design, later changed to a two-hole divided plenum. When the Holley three-barrel carb came out, the aftermarket intakes got a notch in the plenum divider to clear the rear “barn door” throttle plate and the intake was designated “_3B”.