VW was able to get more power with the eco diesel because of the turbo. At a given rpm, the engine can only suck so much air, and the injection pump was set to supply only enough fuel to go with it. With the addition of the turbo, the injection pump could be set at a higher injection quantity compaired to the NA car, because the turbo was pushing in extra air to burn all the fuel. The injection quantity is dependant on the fuel screw setting and your foot. If you pushed the car to the floor at low rpm, it would be rich untill the turbo spools up to clean up the smoke and burn the fuel. That would only last for a time it takes the turbo to spool though. When cruising around even with no boost, you wont be running rich becuase the pump wont be injecting more fuel than the engine needs, unless your foot tells it to do so. The Turbo diesel did get less mileage for a couple reasons. You are right about the luxury options, many of the regular diesels did not have power steering, or a/c. Most all the turbo diesels had those options, along with cruise, some had sunroofs, and I believe the turbo diesel had a different final drive ratio, or 5th gear I cant remember. I had a '85 Jetta TD that I restored, and have had a number of NA jettas, but the NA cars don't have a tach. I'm just going by my ear at 70mph the TD was spinning a little higher rpm.
Also, look at the power difference of the NA and eco diesel. A whopping 5 hp. Pretty much all the turbo was doing was cleaning up the little bit of unburnt fuel you would have if the car was a NA diesel. In order for a NA diesel to operate with no smoke at all, it would barely accelerate. Some fuel has to go out the exhaust in order for it to have any power at all... That may improve fuel economy slightly but I cant imagine it was that much. I've never owned an eco diesel to be able to tell you what kind of mileage it got. My 85TD however, averaged 42mpg cruising 70mph, which is better than the EPA rating, though I did have a low restriction exhaust system, and was running the timing advanced a little beyond vw's spec.
Hope this all makes sense.
Jason
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