Actually a Speed Density car has no idea how fast the intake charge is coming it. It has no ability to measure the quantity of incoming air, just the air density. A speed density car relies on a database of information stored inside the computer as tables for the injection cycle.
A Mass Airflow car uses a MAF Meter to physically measure the volume of air coming into an engine, then refers to a table like SD.
As far as a speed density system not being able to handle modifications, that's completely false. That's like saying a MAF car cannot handle larger injectors. They both take tuning. You can tune SD by adding fuel pressure, or larger injectors, or having a custom chip burned, and you can tune the MAF to accept larger injectors by having the MAF recalibrated.
There are a couple people on this site in the low low 12's/high 11's with SD.
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