its gear spacing not gear quantity that matters.
you should find that any car, at the Nat Speed Limit of its country of origin, is in its most economical rev range.
i used to worry that my Diesel was at 2.1k on the motorway, when it pulls fine at lower revs, but 2.1k is precisely in the top torque range of the turbo band.
mines an "eco model" too, all that means for me is that the 2L TD engine is tuned to 90bhp, rather than 110bhp, like the rest of the range, but i get 55mpg, where as the rest of them are lucky to top 40.
what WOULD be useful on a diesel cars, is to tune it to Euro fuel standards, where as all production cars are tuned to burn 95% of Diesel availible, including crap yank diesel, and dodgey eastern european Heavy oils. (IIRC)
if you tune the car to the better stuff we have here, you can burn it more efficiently, but they would only work in the EU, and risk damaging the car if the fuel standards dropped too low…..
….as i understand it
which is what diesel "chips" do
very tempted to get one for mine, except 30% increase in power, mpg and torque is all very well, but the suspension isnt designed for it, and it would go through tyres much quicker too…
makes me chuckle, flowing some **** in a chavved up impreza, with the smell of unburnt fuel coming out his big box exhaust, because his "mate works for a tuning company innit"