Oldsmobile started out with very aggressive plans for the Achieva, providing a smorgasbord of engine options, including a 190-horsepower Quad 4 for its 1992 SCX version. But mediocre sales and the high cost of keeping all those choices on the assembly line led to a simpler and more logical powertrain lineup by 1996. The Quad 4 engine, an early powertrain building block for the Achieva proved potent and economical, but lacked truly smooth and quiet performance until major changes were made in 1995. The following year the engine was dropped for a smoother 2.4-liter unit. Achieva loses a little horsepower to stricter emission controls for 1993. The Quad OHC, basic Quad 4, and the two High Output Quad 4 engines all lost 5 horsepower when paired with the automatic transmission, resulting in 115-, 155-, 175-, and 185-horsepower outputs, respectively. Both the Quad OHC and the High Output version of the Quad 4 were dropped in 1995, with the two remaining powerplants for the Achieva being a greatly revised, 150-horsepower Quad 4 and the optional 155-horsepower 3.1-liter V6. Balance shafts are installed in the Quad 4 for 1995 to address the most common complaints--excess noise and lack of smoothness. The new engine for 1996 is a 2.4-liter 4-cylinder, called the Twin Cam. It replaces the 2.3-liter Quad 4. The new Twin Cam and optional V6 both come with new 100,000-mile spark plugs, plus the 100,000-mile coolant.