The s300 is a plug in module to the OBD1 factory Honda Engine Computer (ECU) which vastly expands the capabilities of the factory ECU. Forced induction, datalogging, real time updating of parameters, engine protection are but a few of the s300 features.
Note that there is a rectangular frame ECU version of the s300 and a square frame ECU version (s300J)

 

Connecting the Hondata S300 V3 to your Smartphone

 

 CLICK HERE TO UPGRADE TO V3 FROM OLDER S300