TL;DR: We were vacationing this past week in Orlando. Our goal was to hit the high score on the Test Track leaderboard in which we had almost achieved (matched it at 230). I am pretty sure that the score cap however is 232; I haven’t seen any indication online or in the actual attraction that it can go any higher. We ended up riding test track 3 times, each with the following score: 208, 222, and 230. I am not quite sure where we lost 2 points, I suspect that it was either a screw up when drawing the contour of the car or wheel size. It is worth noting that only higher scores will override the current leader. If you want to stay on the board, ride early.
There are a total of four categories: Power, responsiveness, capability, and efficiency. Your overall score will be the total of all four categories combined. So, the trick is to max out your overall score not just a particular category.
For vehicle type, choose the sports car on the far left. When drawing the contour of the car, you will want to draw something resembling a normalish car shape (small curve for the hood, larger curve for the body). It should resemble something like this:
When sculpting the car, make the tail as tall as possible (drag it to the upper left). For length and width, make the car as short and wide as possible. The hybrid engine is by far the best choice as it gives you an additional accessory slot.
For accessories, the trick is to use the selection that nets you the most overall gain. It doesn’t matter what category it boosts so long as it offers the most points. So for example, if accessory #1 offers +2 power but accessory #2 offers +6 capability and -2 power, you will want to go with accessory #2 because the overall gain is +4 (vs +2). The max amount of point gain for accessories seems to be 20 (front +3, hood +4, side +2, top +2, rear +3, tail +6). Same deal for the wheels. I am not sure if there is an ideal ratio for wheel size.