so I am looking to build a high mpg mercedes. I will sacrifice local road performance (slooooow) and no power for good highway milage since my drive to work is 30 miles highway, 2 miles suface roads each way. I have been trying to think what would giive me the best milage. I am thinking a highway gear or a retrofit 5 speed for od. I am also thinking of swapping the 300D turbo for a 240D NA. I have a few questions. what is the normal milage for a 240D, is it better than a 300D turbo, if so how much improvement could I expect. what is the most efficient highway rpm for the 300D/240D engine? Can i run below that rpm sacrificing some efficiency but netting an increase in milage. does anyone with a 240D 4spd think it will be able to pull its own weight at 60mph with a 5 speed OD trans?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

you should also think of some aeromods. I need to figure out the CD and all that jazz of the w123 sedan. I want to do some mods, reversible and non body harming, to my w123.

So far I want to remove the external mirrors and install interior convex mirrors as well as fab up some fender skirts


The front spoiler you have might help us

the 2.88 gearing is pretty good for mpg's as well.

I think my cd has the 3.07 rear. I think the skirt would hurt to be honest. this car is purely my driver to work so I will do anything reasonable including swapping in a 240D and fabbing a 5spd if it will pull it. Im kicking myself right now for not pulling a 5 spd from a mercedes in the pnp. it was the one with the starter wart on the wrong side but I think I can make that one work.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

You won't get better mileage with a N/A 240. I have a '77 240 automatic and it maybe gets 24mpg if I drive it slow. To keep up with traffic, you have to drive it like a UPS truck..... WIDE OPEN! I know... I have driven BOTH!!

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

To get the best mileage, you'll basically have to re-engineer the whole car. Start with the body. Lower it, install skinnier tires, things like that. Find out how much power it takes to move it down the road at your desired cruising speed. It will probably be something like 22-25 HP.

For the engine, a turbo isn't a bad thing but NA may net you a little better economy because of the higher compression.

You'll need to come up with BSFC (Brake Specific Fuel Consumption) curves for the various engines you're interested in. Find one with the lowest BSFC for the HP needed to move the car down the road at the cruising speed. The graph should also show the RPM where this takes place. Then set up the cars gearing to have the engine run this RPM at the desired cruise speed.

Since I'm not an engineer I would have to come up with this information by trial and error but someone smarter could probably calculate a few things and come up with the best engine combination. Perhaps there is a dyno database on the web somewhere with this info...?

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Word.

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If you really want the best economy, go with a 2.88 rear end, put a shift kit into the tranny so it has a firm shift between shifts and run Biodiesel with a 3* degree timing advance.

Keep your tires properly inflated and the usual. Having to re-engineer the whole car for better fuel economy is too cost prohibitive and you will spend less on fuel than you will replacing motors and the like.

Also, you can use refrigerants like Envirosafe and get great cooling out of your AC and in most states it is legal. This move will save you about 3 MPG alone. It's made in Florida and for sale and use their as well.

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"Extremism in the defense of liberty is no vice and moderation in the pursuit of justice is no virtue!"

The Greatest Arizona Senator ever, Barry M Goldwater. I hope you can see from heaven how much you are missed.

does anyone have the BSFC for a 300D turbo engine? Is this normally given for the engine or the entire car system? I feel with lowered RPM cruising at 65mph max I could realistically get in the 35mpg range. Right now the car cruises at 65 at 3000 RPM, i would like to get the cruise RPM down around 2200. I only have one gear lower to go 2.88. that change only gives me around a 200 rpm drop. right now Im thinking of adapting a 5spd from a 190.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

As stated before, you need to figure out the BSFC for the ENGINE rpm (that's how they're rated) then determine what you'd like your target cruising speed to be. Then calculate what rear end ratio you'd need to have your engine be at the best BSFC for your target cruise speed. This is alot of work but if you're looking to max out your efficiency it really is the best scientific way to do it. Among skinny tires (less rolling resistance), light wheels (less unsprung weight) and aerodynamics (less drag).

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from what I have been reading through from search finds on the subject I think the RPM band I want for cruising at 65 MPH is 2200 RPM. I cant get there with gears, (2.88 will yeild 2800 RPM) the wheels are very light and the tires are not the thinnest but I keep the pressure high. It really is looking like the OD trans is the best solution. this will be easier for me to accomplish in florida since the biggest hill I see is the bridge over the bay, besides with a 5 speed I can always drop to 4th for hills and still be the same as I am now.

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

Nah, you need a different engine, i.e. you need to reengineer the engine.

The current common-rail diesels can provide almost twice the power while getting around twice the fuel economy.

That's not going to happen playing around with 30-year-old designs.

The best bet is a 2005 E320CDI or if you're willing to go smaller, a VW TDI. The W123 is a money pit when it comes to trying to get close to these.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

I'm running a 2.47 diff from an 83-84 380SE, in my 300CD. Although some have said it would be too tall, and would lack power that is not what I am finding at all. In fact I hope to find another 2.47 to put in my SD. I am also running the vogtland springs which as well as really improving handling has dropped the height of the car, and reduced drag... I hope.

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

I would look for a 190D 2.2 with a 5 speed.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

You need a hydrostatic regenerative brake.

http://www.boschrexroth.com/country_units/america/united_states/en/news_and_press/press_releases/brm/Rexroth_Hydrostatic_Regenerative_Brake/index.jsp

This company says it can be retrofitted to existing vehicles but I think they have trucks in mind.


Seriously though, diesel engines typically get their best fuel economy between the rpm their torque peaks at and their power peaks at. (what a great excuse to go get a dyno run ) This should help you figure out gearing.

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green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

http://ecomodder.com/forum/fe-graphs/sig692a.png

what kind of MPG numbers are you getting with the 2.47, those would get me in around 2400 RPM at 65? I also have a set of vogtlands, just have not installed them yet

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)