No self combo's for engi. I capped all three toons and found engineer to be the slowest. Lack of damage output is all it boils down to. Maybe you could talk to Lelouchx (his engi is named Eyeofnewt), Deathpunch, Morfic, Bubu, or Bene. They know Engi's very well and are also friendly. I'm sure they can help speed up your runs.