The big news for the 2006 Mercury Mountaineer is the new engine. Mercury has developed a new three-valve, 4.6-liter V8 that is more powerful yet 22-percent more efficient than the V8 used in last year’s model. The new V8 dishes out 292 horsepower vs. the old V8’s 239 horsepower. A new six-speed transmission handles the V8’s output, while the standard, and cleaner-burning, V6 is mated to last year’s capable five-speed transmission.