I come from an electrical engineering background and I like building things myself, so lately I've been toying with the idea of designing my own data logger and real time display for driving. However, I'm still learning my way around cars so I don't know what would be good variables to keep track of. I was thinking air temperature at the intake would be nice to know to keep an eye on heat saturation for a short ram intake. Possibly monitor the oxygen sensor or fuel mixture, if that would be of any use. I was also considering reading the fuel level gauge and display it on a scale of 0-100% instead of the normal dial. This would also allow for another feature calculating fuel economy for each trip. Basically I'm looking for information I could read off the car's sensors (or other sensors that could be installed) that would allow the driver to drive the car most efficiently or powerfully. Any suggestions?

Keep in mind I'm not looking to get anywhere near Hondalogger or anything like it. Just looking for a few things I could display on the dash board that would be useful to know for the sake of knowing or to better take advantage on the car's capabilities. Thanks for any ideas.