what do ppl mean by mass air?
Speed density uses map sensor. It is less tuneable. Mass air pressure vs mass air flow. Mass air meter measures the amount of air coming in to determine how long the squirters stay on. The more air, the more fuel, the higher the rpm in laymens terms. Its been a while since I talked about this stuff so I could be rusty. You can google all kind of info on them. I am sure someone can ellaborate on it.
or you can read his link. I type too slow!