The M Pump is rare on W123s because it was only available on european cars. However, it doesn't offer and advantages that I know of. I just put a european 617 engine in my 300CD and it honestly isn't anything spectacular, other than is lacks all the emissions stuff. From what I've read the motor itself is off higher compression, taking advantage of Europe's higher-cetane rated diesel (can't confirm). Performance-wise I can't really say...

A 617 with 380 ponies? Even the C111 only mustered 230 hp.

http://www.classicdriver.com/uk/magazine/3200.asp?id=11583

The Fins work magic with the 60x engines, but an iron five pot?

Jay

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On the road, currently:
'83 300D (German spec.) 168k mi. - - Wolfgang (tucked snugly away for the winter!)
'87 300D 375k mi. - finally went over to "The Dark Side"
'87 300TD 225k mi.
Cannondale 66cm CAAD5 w/Campy/Jamis Aurora
Hujsak Custom Fixie/Landshark Track Shark Custom/Ahearne Custom 29'er

the non-turbo engine is identical to the american version other than the injection system and emissions. the euro turbo engine is the same minus the EGR.

the m-pump has different elenents inside than the mw pump does. myna does not touch the mw, only the m pump. bottom line, mo' powahh, but mo' money.

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1981 300 SD 213k miles "Stock for now"
1999 Super Duty 7.3L 113k miles
1981 300 SD 180k miles "Heavily modified" SOLD

The green wagon had that. With the M pump there are stock upgrades that you can do. With the MW pump there are aftermarket elements that you can upgrade with. The MW is considered technically superior, they tend to last longer and are easier to calibrate.

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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