I think if you have an old design of engine block that wasn't particularly well gas flowed, then one of these might help it out, however, if you've got a decently modern engine with flowed ports, then they probably just take up intake area.
I just thought of an item that would be perfect to try in an air intake for an injection system, it's the top off one of those balls you put in the washing machine. There were some selling a few years back for a concentrated powder, not a liquid, that had a kinda swirly fan type thing in the top, maybe 3 inches across or so. Wish I had one around, I'll keep an eye out.
Road Warrior