Just had a quick browse of the
http://www.massfloefi.com site. It looks like a great system but I think they may be a little misguided.
Here is a quote from the site: "Any naturally aspirated engine, regardless of brand, size, combination of parts, etc., requires a given air/fuel ratio, at a given load. These ratios do not change from engine to engine, until you get into forced induction applications. (We'll get to that later). The needed air/fuel ratio changes with such things as engine temperature, air temperature, and atmospheric pressure, but the needed changes, again, are the same for all engines."
Mmmm, interesting.......