617 na vs turbo US spec vehicles with the auto trans get lower economy due to the short diff, and the slipping torque converter.
It isn't really the turbo that gains economy in the aspirated vehicles... it's the diff change.

Put the 3.07 or 2.88 diff behind the na motor, and economy would go up... of course, it would take a month to reach 60mph... the trans gearing and shift points in the na vehicle also hinder economy in favor of spirited city driving...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!