The Chevy Lumina would be the perfect illustration for the "car" entry in an encyclopedia. Forthright and foursquare, the standard Lumina has all of the basics and none of the frills. It is sturdy, reliable, roomy, and inexpensive. It scores near the top of the charts in crashworthiness and at the bottom in theft rates. With traits like those, you won't be surprised to learn that the Lumina gets little respect from car buffs. Neither will you be surprised to learn that the Lumina was among the top ten in sales last year. A good honest car at a good honest price will always have a market. But another thing that never fades away is the desire of engineers to add performance. This year, Lumina engineers pieced together the new Lumina LTZ, a high-powered sporty edition for buyers who need the room of a Lumina but yearn for a little more verve.