Conversation so far:
when did Alan Kulwicki start racing?
Alan Kulwicki began his racing career as a 13-year-old kart racer.
who made the karts for Alan Kulwicki when he began his racing career as a 13-year-old kart racer?
Alan Kulwicki's father built engines as the crew chief for Norm Nelson and Roger McCluskey's United States Automobile Club racecars.

Question: when did Alan start racing cars?
Self-contained rewrite: when did Alan Kulwicki start racing cars after his father built engines as the crew chief for Norm Nelson and Roger McCluskey's United States Automobile Club racecars?