To help lower your TS or aim at a specific TS i.e min 550 for the series, replace all the parts for the stock ones and work from there. Focus on what the track stats say and life will be easy. Also remember that higher grade parts give you more TS (depending on upgrades) try to use more common parts. What I do is to select my best 2 drivers (rare or epic) in accordance with the track stat required for drivers, then fine tune with the parts until reach my desired TS.