Tuesday, March 10, 1992 What does a German luxury car maker do when Lexus and Infiniti up the cylinder-count and horsepower ante? If you're BMW, you match on cylinders and raise the stakes on power.
The Munich-based firm unveiled new V-8s in 3.0- and 4.0-liter sizes at this week's Geneva Show. While the engines will first appear in the current 7-series sedan (in 730i and 740i models), they'll eventually find their way into the 8-series coupes and the 5-series four-doors, and -- for a particularly potent combination -- even the small 3-series sedans.
The new powerplants follow most modern trends: They use overhead camshafts to operate four valves per cylinder, have both block and heads cast of aluminum, and rely upon an integrated, electronic engine management system to control both fuel injection and spark timing. A hot-film air-mass sensor measures air flow.
More unusual are the engines' undersquare bore-stroke ratios: the smaller engine pushes tiny, 67.6mm pistons through 84.0mm strokes, for a 2997cc displacement. The larger V-8 is slightly less undersquare, but still combines 80mm bores with long, 89mm strokes for its 3982cc. As a consequence, very compact combustion chambers result, and help allow the three-liter engine to live with unleaded gas and a high, 10.5:1 compression, the four-liter with a 10.0:1 ratio. Bore spacing of 98mm, however, indicates that BMW is leaving room to make the engines either larger or less undersquare in the future.
The new powerplants easily outpower the sixes they replace, and at least one of their Japanese competitors as well.
The smaller V-8 peaks with 218 horsepower at 5800 rpm, and 214 pound-feet of torque at 4500. The 4-liter engine makes 286 horsepower and 295 pound-feet at exactly the same engine speeds. Though the torque peaks are seemingly high, BMW claims the torque curves are particularly flat.
BMW's strongest six, the 3.5-liter, made only 211 horsepower -- 7 horsepower less than its new 3-liter V-8 -- and even its 5.0-liter V-12 carries only a 14-horsepower advantage over its new 4.0-liter powerplant. That V-8 handily wallops the Lexus 4.0-liter eight-cylinder with almost 15 percent more horsepower. The new engines are commendably light as well, at 447 and 466 pounds respectively, only slightly heavier than the 433-pound sixes they replace.
Sales of the 730i and 740i begin in Europe this spring, and in the U.S. in the fall.