The new SmartyCam HD Rev. 2.1 is the only onboard camera designed specifically for motorsports.  It allows you to overlay nearly any parameters you want such as speed, rpm, lap times, lateral g’s and so forth.  With the free Racestudio3 software you can configure your overlays, split laps and do in-depth video analysis that is impossible with any other action camera.  This thing makes a GoPro look like a Betacam. Free shipping on this baby too!