The car looks pretty good. However, I recommend using Serpentine (which is the font they use for their numbers) as the number font instead of Bullet (which you used).
Make the lines follow the body contour. It looks like you just used a selection tool and made some rectangles. But I like clean designs like that. I doubt the number font is really going to matter to them. They're going to have to do some new ones anyway if they're using the 30.
When they announced they were moving to cup the number style was different, it was more like #90 of Keyed-up Motorsports and I didn't like it...Glad they changed #30 style, looks more sharp and agressive. BTW, I like the design you did DanicaFan (y)