Conversation so far:
When did Juan Manuel Fangio's racing career begin?
He began his racing career in Argentina in 1934
Did Juan Manuel Fangio perform well at the beginning of his racing career?
Following many successes driving mainly modified American stock cars; he was funded by the Argentine Automobile Club and the Argentine government and sent to Europe in 1948.
What type of car did Juan Manuel Fangio drive in the Argentina race?
During his time racing in Argentina, he drove Chevrolet cars.
Was Juan Manuel Fangio a champion driver?
He was Argentine National Champion in 1940 and 1941
Did Juan Manuel Fangio travel?
Fangio traveled to Europe.
Did Juan Manuel Fangio have sponsors in his early career?
Automobile Club of Argentina
Were American cars used in Juan Manuel Fangio's early races?
Modified American stock cars

Question: How did they fair?
Self-contained rewrite: How did the American modified stock cars perform while driven by Juan Manuel Fangio?