If you want a slaughter win the Ruf Yellowbird from the Tuner races, or wherever it comes from and use it.
It will require some tuning and futzing.
Or if you happen to be used to lift-throttle oversteer just get off the throttle going in to sharper turns, and get back on-throttle when the car is facing the direction you want to be going.
You can also take the Subaru Rally car you win in the Special condition races and use it to great effect, or take it to the manufacturer's cup and win the Impreza LM car to use for this.
For something a bit more fair, pick up a used WRX, change the oil, tweak the suspension and the gearbox, and you should be able to sweep the series, but not too easily.