Since I'm "good with computers", I would always help them with their electrical issues, which eventually evolved into me tuning their cars and dealing with any other EFI related issues. Most tuners charge around $500, but I do it all for free, so that helps.

If you really want to get involved, seek out some car clubs in your area and check out some of the open source ECU projects (such as Speeduino). Usually, car hobbyist can be identified by a group of people standing in a parking lot staring at their cars. Most of them love to brag about their setup, so they're pretty receptive to people asking questions.