Test #'s I've seen stock to stock, .500" valve lift,28" water - CFM:
3V 235 intake, 159 exhaust
99 Cobra 4V 243 intake, 169 exhaust.
PI 2V heads 170 intake, 150 exhaust.
So, although the 3V heads (stock to stock) aren't quite as good as the 4V, they are a huge improvement over the 2V...