Each successive generation of BMW's iconic 3-Series has grown in size and price, leaving the door open for a new entry-level model. BMW has introduced the 1-Series coupe and convertible to fill that opening. Compared to the 3-Series the 1-Series is about 9 inches shorter, 2 inches narrower and a couple hundred pounds lighter. The good news is that the same two six cylinder engines power the smaller car. A 230-bhp inline-six resides in the 128i, whereas a 300-bhp turbocharged version powers the 135i. A smaller car with the same power could make the choice between the two tough for prospective BMW buyers. Although the starting price is low, options and packages can add thousands to the price.