It really depends a lot on the track you plan to run at...
Servo's - I'd recommend a quality servo - KO, JR, Futaba & airtronics are popular and reliable, lean towards less power, and more speed for steering (for example a KO PDS2367ICS), and more power (for example a PDS2386ICS) for throttle/brake.
As for motor, those can be pricey, and it's not always necessary to spend big bucks. Once again, depending on the track, (less traction, parking lots or smaller tracks), a good little budget motor (novarossi Kangaroo) will do perfectly fine, the higher big cost/horsepower motors can get a little sensitive to tune, and typically are best suited to more grip longer tracks..
I'd recommend going to the track you plan to race at, and check out the drivers's rides.. Knowing "what's popular" at the local scene goes along way during your race day, especially when you may need a spare part, or suggestion of what combination works best on the track..
1/8th scale onroad is an exciting sport, and the pinnacle of on-road racing. Enjoy.
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