This may help, but you will need to recalibrate your speedometer.

I like the idea of a manual transmission, but it's a bigger challenge to find & install.

For a car out on the highway most of the time...
looking for a different gear ratio for the Third Member is way easier to do...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

The difference between replacing the torque converter and installing a manual, labor wise, is the pedal cluster. Not a big one..

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Actually the main problem in doing it right...
is finding a 617 FLYWHEEL......
many wind up using a 616 flywheel.... and many of those report a vibration which they never find the cause of....

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

Done
Schwungmasse Kupplung Mercedes G G-Modell G-Klasse 300GD OM617 460 461 flywheel | eBay

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CENSORED due to not family friendly words

Now, wouldn't a faster spooling turbo allow to get better torque at lower RPMs?
Lowering peak torque RPM would increase the MPG i imagine.

__________________
General George - 1967 Land Rover 2a SWB 1983 OM617 Turbo

Ding ding ding ding ding!!!

We got a winner

__________________
CENSORED due to not family friendly words

If he could stay out of the pedal sure.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

I have like a 5 speed in the 300sd would suck. It feels so much bigger than my 300d.

__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800

According too many hyper-miling sites going with a lighter weight differential motor oil and synthetic transmission fluid will help.
There is a tire called ecopia that is supposed to give you a 1-2 mile gain.
Believe it or not, but mudflaps will actually improve aerodynamics and reduce drag.
.