I bought a previously raced 2004 Cavalier which ran very well --points leader. In the FAQ Somewhere I saw a stern warning not to use 10-40 etc. oils, 10w30 ONLY. Why not? What would be the problem with a 20w60 racing oil?
I run what the factory calls for. 5W-30..I also use full synthetic and never had a problem. I change my oil every 3 races and add a 1/2 of quart extra.