Conventional wisdom says that a rectangular port should be at least 88% of the valve diameter in cross-sectional area, and 80% for a round port. If the valve is 1.940", then the area of the intake runner should be at least 1 3/4" minimum, and for higher rpm, I think bigger would be better. A taper is always a good idea in the intake manifold port to the head. A small amount of taper is all that is necessary, as long as there is a continuous taper, and not an area for reversion. That plenum looks small on John's intake, so the spacer must be making up the difference for it to work that well. Joe-JDC.