Del Sol S - SOHC Non-VTEC
Del Sol Si - SOHC VTEC
Del Sol VTEC - DOHC VTEC

the motor will clearly say DOHC VTEC on it.

By the way... the DOHC VTECs weren't made untill 1994.
If you can, try to find a 94 or 95 Del Sol VTEC... they still have the OBD1 ECU (older emmision standards computer) They take a little better to modification.