The LD4B test on the 340 suggests that generalization probably doesn't hold in this case. The factory needed a low hoodline intake that performed well on the street. The LD series were focused on better high rpm. The LD4B has fat runners (although they do taper down to the 318 port size) and this is probably where at low rpm velocity is lost in at least some of the runners. On the other otherhand If low and mid throttle manifold vacuum is high enough, it might not make a measureable difference.