That's the same MPG I average with my 420. And its always under 2,200rpm in the city easily....the engine is bored under 55mph. The other day I was making a turn on dry pavement and kicked it down to 1st/floored it and completed my turn with tire squeal and some drifting action. That's what I am talking about Lets see an an M103 do that in a W126. It can (sort of) in a W124....but its just not the same. Its all about the torque in a huge car like a W126.

Keep in mind the V8 can light up the tires like that with a 2.47 differential. The M103 has like a 3.69 or something and is still slower.

80Mph in my 420 is about 2,900 rpm and silent.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

My 350 will do this too

I would personally go for the V8 gas over the I6 gas engines though, since the economy isn't hugely different and it seems like the V8s are a better match for the car.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Any M103 will make substantially more low end torque and noticeably better fuel economy if you remove the R16/1 resistor.

This will create the most aggressive centrifugal spark advance curve. I can even get away with 87 PON fuel on my 190E2.6 five-speed as long as the engine temp is about 80C and ambient is no more than 70F. Above these temps I pick up a little transient detonation on upshifts, but it's easy to drive around by shifting higher than my normal 2000.

With the above setup it may fail field emission tests. The best set up for emission testing is to short the R16/1 plug. This will yield the slowest centrifugal curve, which lowers peak combustion temperature (less NOx), but increases EGT to keep the catalyst hotter. (But it won't get out of it's own way below about 2000.) Blocking the vacuum advance signal line will further aid in passing emission tests.

With the OE 750 ohm resistor I got about 18-20 MPG around town and high 20s on long freeway trips at 75-80. With the R16/1 removed around town fuel economy shot up to 22-24 MPG (about the same highway), and I can drop it into fifth at 35 MPH. Before, fifth was unusable below about 45 MPH. These are the effects of a spark advance map optimized for performance and economy rather than emissions.

I've known a couple of folks with 300SEs. They are very nice "town cars" with a first gear start. Most find the engine too "busy" at highway speed, but the engine is very smooth and quiet. They just get upset about the high tach reading.

There's lot's of information on the R16/1 resistor, including where it's located on your model, in the archives.

Duke

Interesting comments about the M103. I find the engine perfectly suitable in my 300CE. Then again it is the smaller body. I also get no less than 20 mpg in mostly city driving. I would agree though that the larger body W126 does seem better suited to the V8 if you had the choice. I wish the rear end was geared lower. 3k rpms at normal highway speeds is not ideal.

__________________
1989 300CE

I tried the resistor removal on my W124 with the M103 when I had it...there was no change in performance at all....I did the same to my current 420 with a noticeable improvement. Very strange...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

IIRC the various resistors allow the same total centrifugal advance, but the lower the resistor value the quicker it comes in down low. I think by about 3000 they're all the same.

It's probably less noticeable with an auto trans and a short axle ratio than a manual. The converter will not allow you to load up the engine at less than about 2K revs, but a manual can be loaded up down to literally idle speed.

My five-speed easily pulls from 1200 in fifth and has seriously more torque in the 1500-2000 range with no resistor The overall ratio is .8(3.27) = 2.62, and 1200 in fifth is about 30 MPH.

I usually drop it into fifth at 35 MPH and don't need to downshift until I'm below 30. As I said previously with the OE 750 ohm resistor fifth was not useable below about 45 MPH. It just wouldn't pull, and that lack of low end torque/power meant that the engine was operating at low thermal efficiency because so much energy was being thrown out the exhaust in the form of higher EGT.

Getting the low rev spark advance more optimized yields greater low rev thermal efficiency, which means more low end torque/power, and being able to run a gear higher in most around town traffic is why my around town fuel economy improved by at 10-20 percent.

Duke

^^^

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

The 240D is a 3.69. I think the M103 is a 3.46, same as the 300D NA.

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Yeah that's way too high, 4k rpm at 70ish mph on the freeway is ridiculous. It would work much better if the transmission had been a 5 speed or had overdrive.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The W126 M103 would have benefited from much better rear end gearing, also first gear start. Without those its rather piss poor.

My W124 M103 (91) gets about 18-20 in town, and a solid 25/26 highway. All time best MPG highway was 27. But its in perfect tune.

In the last year or so there was a long thread started by a 300SE owner who replaced the 3.46 with a 2.47, and he had some issues, but I think he eventually got them resolved.

I know I made several posts to this thread, so you might be able to find by searching for posts by me. There are very few in the last few years.

Many complain about the high revs at freeway speed, but installing a tall gear causes another set of problems.

It's tough for a small displacement engine to accelerate a heavy brick through the air.

Duke

The Kjet m103 is a pathetic excuse for an engine even in the small w201 body. Switching it to EFI was a huge improvement bit it still lacked the low end torque and ease of maintainance of the M102 8 valve in the same body. I would hate to get stuck with a 3.0L m103 in something heavier like a w124 or w126. The om603 has torque down low where you need it to get moving even before boost.

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CENSORED due to not family friendly words

I played around with the R16 resistor when I had the 2.6 5spd and it does indeed make a difference but not enough to make up for its faults. With EFI the loaded up car returned 31mpg regularly on long highway trips and low 20s in the city. That was about the height of its qualities.

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CENSORED due to not family friendly words

Just make the thing scream. Yes, the M103 is pretty weak below about 3.5K rpms. Keep the revs up and it's fine. It almost has as much hp as the contemporary 420, and it weighs a bit less. Making overall acceleration theoretically par for par.

I had no problem with the SE when I had it. And I was perfectly comfortable with the power. You just have to keep in mind, at what point in the power band you get the most shove. An engine like this would've been perfect with a manual transmission. And the revs never bothered me...The engine was designed to be a screamer in the first place. You're not gonna hurt it.

__________________
1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)