I had a 73 Camaro with a 350 2 barrel. A buddy had a SP2P and a Holley 600 for $35. I saw the chance to swap to a 4 barrel and jumped on it. I know the car was louder when the secondaries opened but I don';t recall if the car was any faster.
Many years later, I put a mild 360 in my 67 Dart. This was a REAL budget build. Lots of junkyard scrounging, etc. A guy in our Mopar club had a LA SP2P for $40. The engine was a reringed 360 with a mild cam. It felt as if it got slower the further I pressed the accelerator. I first blamed the cam, thinking maybe I had installed it a tooth advanced. I stumbled upon a Weiand 4 barrel intake with much bigger ports at a junkyard. The car felt transformed with that Weiand. I am convinced that the design of that intake sucks ass from the crack to the sack.