look not bad mate. i have as yet not photographed rc but i regularly take pics off ice hockey which is just as fast paced.
manual is the best way forward to get the higher shutter speeds. With the rc im guessing you can kind of plan on where cars will be coming through. try manually focusing at this point then firing them off as the cars pass through. if its jumps your looking for try setting up before the race and getting a friendly marshal to stand in the area where the cars will be in the air giving you something to set your focus on before the race starts.
just my thoughts im far from a pro at this but its things i would try.
looking forward to seeing more photos soon
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