The SD mod is about replacing MAF with MAP indeed. Some Evos have a SD / MAP system by default. For some you need a Ceddy ROM mod to add support for SD. In the VR-4 this was implemented by @Kenneth in a special version of his ROM.
http://www.clubvr4.com/forum/showthr...-based-tuning)
Not much interest in this mod though so far. As far as pros/cons that I can see:
Pros:
- Removed MAF related restriction on intake
- Open BOV friendly
- Not bothered by vacuum leaks like the MAF system
Cons:
- Complicated to set up due to the need to populate the VE (Volumetric Efficiency) table to even get it working
- No instant power or economy gains. In fact expect both to be worse before you dial it in.
Also I reckon that since the SD system can reflect engine load changes much quicker than MAF it will require major tuning in the stock ROM to at the very least remove (or dial down) the acceleration enrichment.