How come speed density limits the mods you can make to your motor (ex. supercharger, turbo)? If you are essentially putting more air into the cylinders, won't the manifold pressure increase, and therefore the fuel injected will increase?
The problem is not speed density EFI. The problem is Ford speed density EFI isn't very hacked and difficult to work with because most of the Ford EEC editors (freeware and commercial) really do not support these EEC's very well, if at all.
Of course if you're familiar with the Intel 8051 processor and have countless hours to reverse engineer a particular ford EEC down to the source code level, you can make that EEC do anything you want - even control Christmas lights.
See, things like Tweecer and similar products focus on Lightenings and Mustangs, because those are the vehicles typically used as the foundation for high performance "street toys" that will have forced induction.
As stated the Ford SD system is compatable with forced induction because these kits include an FMU to boost fuel pressure so no extra tuning is necessary. SD is only restrictive when it comes to naturally aspirated mods like cams and heads because the computer is programmed for a stock motor and has no way to recalibrate itself to these high flow components, and in general isn't supported by aftermarket tuning systems.