Ah, what you are creating is not a vector. What you are doing is manipulating a photo in a photo editing program (GIMP or Photoshop I presume?).
Vectors are created in applications such as Adobe Illustrator or the free, open source Inkscape. They work very differently than what you are doing. You are doing what is called bitmap editing. As you know, there are pixles that make up your image. In a vector, there are no pixles. Instead the image is made up of mathematical formulas for shapes and lines. For more info: http://www.eastbywest.com/pub/vectorbitmap/
In creating a vector you load up the image of the original M3, and then you use a special tool to trace it. Essentially you click two points to form a line, and then you bend it around the shape of the car component you are tracing.
This was my first ever vector image, a very basic example of a vector. Ignore the JPEG artifacts, and you see that the image is made up entirely of shapes that I traced from a real photograph.
Here's another example of how they look (with additional version showing outlines).
I don't recall the time I put into doing that particular vector, but I remember it was a LOT (like on & off for a week plus).
You can certainly do vectors in Photoshop (a good number of people who post here do), but I find Illustrator is best for me. Besides, that's what it was created to do.
Thanks for the clarification. That Lotus looks awesome. Yeah, I can see why it's time consuming. I'll have to look up more tutorials to get it right, but right now I don't really have the time.