• Mar 3rd 2008 at 11:54AM
  • 7
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!

[Source: AutoExpress]

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    • 1 Second Ago
      • 7 Years Ago
      What's keeping them.
      Diesel Forester for 2009 would beat the rest of the pack....I need to trade in my Outback NOW.
      I need Diesel NOW.
      It would be my tird Subaru.
      But , if they're going to be that late I will buy a Honda CRV or VW sportwagon or VW Tiguan.
      I'd rather have a Subaru Diesel.
      Looking forward too, to a Diesel/Hybrid,.
      What's keepin' them??????
      Take my $$$$$$ now.
      • 7 Years Ago
      I would shocked if Subaru sold an STI diesel. I would be equally shocked if they did not offer a sporty diesel version of the Impreza, at least in Europe if not here too.
      • 7 Years Ago
      I meant to also say that I would run the diesel Forester on biodiesel as I do with my 2006 VW NB TDi.
      • 7 Years Ago
      I don't believe the diesel really needs extra horsepower if torque numbers are approaching 300 (which is as good as the current gas STi), but I'm sure a little massaging of the engine will shoot up about 10-15 more hp, but more importantly 13-18 lb-ft torque. But even if less than 10 for each, although I think they will, this will still be one awesome car! Definite keepsake in my future garageplex
      • 7 Years Ago
      I own a 2004 Subaru Forester XT. Because of the gearing in that year, the thing does 0-60 in 5.3 seconds. It's an absolute sleeper beast.
      Having awd, lots of room for my kids/dog/gear and great crash ratings make this car incredible. But the gas mileage does suck. If there's any chance of converting it to run on e85 (if it becomes available without the inefficiencies of using corn), I would keep this car forever.
      However, if they offer a diesel Forester in the US, I would buy it in a heartbeat. Then, I'd chip it, give it better suspension, etc. and make my own diesel XT STi.
      • 7 Years Ago
      It's quite likely that Subaru will shoehorn its new boxer diesel into every suitable platform, at least for the European market. There are indeed rumors that Subaru has a diesel Impreza STi in the works.


      However, tuning a diesel engine to deliver 180hp instead of 150hp is easier said than done, because the combustion properties of diesel fuel inherently limit engine speed. True, Audi has managed to push the envelope to 5000 RPM, but Subaru is new to diesels and its design is limited to a more usual 4500 RPM.

      The only other way to increase rated power is to increase torque at high RPM. The torque curve of the Subaru diesel is artificially limited to 350 Nm (~260 lb-ft) and does drop off starting as early as 2500 RPM.


      Presumably, the single variable geometry turbo is currently optimized for low lag and high stationary torque at low RPM. The trade-off is reduced torque at high RPM, something a larger turbo can remedy. More elegant but also much harder to execute is a sequential turbo setup.

      Either way, boosting power has significant implications for the cooling system of both engine and turbos as well as those all-important drive cycle emissions.
        • 6 Years Ago
        What are you writing about?

        I drive a Mazda6 station wagon turbo diesel, and I regularly push her to 5,000RPM without any problems.
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