muscle cars? grid or shift2 are for you. applying physics models and other mods will turn them from arcade racers to gt5 beating sims.
+1 on Grid and Shift2 (with Shift2 being more sim-oriented).
Next year Project C.A.R.S.
will be coming out, and I have a feeling it may turn out to be the best one yet. It's being developed by SlightlyMad (same dev as Shift2) and is looking pretty fantastic at this point.