When using a smaller diameter pipe, at the same engine rpm, the intake air would have to be moving faster through the pipe, that´s just physics. But the speed effect would be negated when the diameter increases at the TB and then into the intake manifold. I suppose that only somebody like Blade running turbo would notice the effect of a smaller diameter pipe, since he´s pushing more air through a smaller pipe, intake velocity would be even greater, resulting in increased cylinder filling during the intake stroke... It´s all theory, but hell, it might make a difference?