How important is mass air on a pre 89 fi

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Hello cool site, I bought an 88 mustang gt convertible back in November "my first ford". The car needed alot of work I have since added BBK equal length headers, mac cold air intake, 8mm wires, flowmasters h-pipe, a cowl hood, pony rims and seats out of a 95 gt. The motor is a rebuilt 306 is still is pretty fresh. Ok what is the purpose of going from speed density to a mass air set up. Any input would be greatly appreciated. I neglected to mention that i also have purchased nitto drag radials and a ford racing clutch. Any gueses as to what my car would run . i havent got to run it yet.