hondata modifies standard OBD I ECUs, adding features and expanding the capabilities of the ECU (like read boost). you can control vtec crossover points, adjust rev limits, remove speed limiters. in short, it removes the lmits of your stock ecu. very good mod for boosted cars, but can also work well in n/a cars. expensive and can be a PITA to tune but once you do, you'll see soem nice results