tm2003:
I used the Camaro racecar for the Beginner Stars & Stripes, because it was the only American car I owned at the time. It was pretty much a slaughter.
One thing you definitely need is at least T2 tires, or T4s. These really really improve your grip.
The next thing is a milefile said - brake early for most corners, and avoid braking while turning. You should brake early enough that you are back on the gas before the apex of the turn, after a brief pause for turn in. You'll be surprised how much that will smooth out your turns and speed up your laps.