The power output of a siren in terms of air movement depends on the amount of trapped air and the pressure a rotor attains during the closed cycle versus the time the air has to escape during the open cycle, which is why the ports are always equal in width to the walls of the rotor - too big a port, and you'll lose compression; too small a port, and you'll lose maximum attainable air output. However, since the supposed rotor with sixteen ports has half the compression time between bursts it only loses about half the air in return per port, displacing the air at about the same output speed per chop as the eight-port rotor, assuming both are running at the same speed, considering both rotors will achieve approximately the same negative pressure on the inside.
Yes, there has to be a certain minimum number of vanes for efficient suction, but I don't think eight-versus-sixteen would make too much of a difference in suction, as long as the volume between the vanes matches the rate of chopping.
Going back to my second post as well as Richard's first post, talking about propagation, would it be possible for a humongous sixteen-port rotor to produce nearly the same propagation as a normal eight-port rotor half its size due to the fact that you will have nearly the same amount of air exiting per chop? I'm thinking that since the high rotor will have shorter chops regardless, its double size would make up for the loss of output time. It may be extremely difficult and inefficient but would be fun to achieve better penetration with a high pitch by ridiculously increasing the physical size of the chops, though there really would be no point to it in the end.
Here's a more practical analogy as to what I mean in general. Let's say you have two identical plastic bowls; you place one on boiling water and the other on a working hotplate. Both the water and the hotplate are set to the exact same temperature, so both the water molecules and the iron atoms in the hotplate have the same relative average power acting on them individually. At about boiling point, you'll notice the bowl floating on the the water start to move up and down while the bowl on the hotplate is just standing there. Both the bowls are receiving about the same amount of power from their own sources of heat, yet one bowl is moving. Why? Because the water particles are allowed to move longer distances even at the same temperature as the iron and therefore move the bowl. The iron just vibrates randomly about a few nanometers back and forth and so does not move anything. You could double the temperature on the hotplate and you'll still move nothing. The hotplate represents the high rotor, while the water represents the low rotor.