First,
Car Reviews: Get a few car mags (e.g.: Bottom Gear,First Gear, Manualcar,etc) to review your cars. And maybe at the end of year, a Car Awards ceremony.
Second,
Engine sales: Sell your nice I4 engine to [CAR MANUFACTURER NAME HERE] for them to put in their [CAR TYPE NAME HERE].
That is all.
P.S.: For your (possible) future DLC Racing Team Manager, you can get a few people as sponsers (e.g. Bloody Mary, Full-Death 2, Untrusted Bank Takeovers)