I recently had the opportunity to spend some time with a 2008 Subaru Impreza STi. As a sporting rally-bred machine, the STi has some serious performance credentials. When you really crack the whip, the STi will get to 60mph in about 4.9 seconds. The problem is, for a relatively small car, it consumes quite a bit of gasoline in the process. During the time I drove it, it only averaged about 18mpg. It also takes a lot of revs to get it to really go. Below about 4,000rpm, the STi engine feels pretty gutless which means it's not all that much fun to drive around town. Now that Subaru has a diesel engine available in Europe and coming to the U.S. in 2010, the speculation is starting about a diesel-powered STi. The current diesel has 148hp but a tuned version could easily put out 180-200hp. More importantly, with a potential 300lb-ft of torque that would surely be available below 2,000rpm this could make a seriously fun car with 30+mpg. Bring it on!