70+ MPG for Diesels in Europe? What are we missing? - PeachParts Mercedes-Benz Forum

cirrusman · #1 11-17-2009, 10:38 PM

Here's where my question comes from: http://www.youtube.com/watch?v=WjnkM9Ws9Fw&feature=PlayList&p=F3CA9344931851E4

So, this guy's diesel VW is averaging 70+MPG.

The monstrous Jag's V-8 is averaging 50+ MPG. The other Subaru Diesel is doing something like that. How come I can only get 21 to 25 MPG on my 3.0L '83 300SD? OK... I turned my ALDA's bolt half a turn CCW to get a bit more oomph pulling away from a red light and it did work, unfortunately with a noticeable decrease on fuel economy. I used to get 25-30 MPG before that (I averaged 37 on a 200 mile trip I did once and I was so thrilled...), but oh well. Anyway...what are they doing that we're not? I'd like to know if there's anyone out there with enough technical knowledge as to suggest a couple of mods I could do to my OM617 engine... besides them HHO producers, which sound a bit fishy to me. Any suggestions?

#2 11-17-2009, 10:54 PM

Well you can't compare a 1970s design with a current design, and the VW weighs about half as much. The new CDIs get decent mileage, about 35 mpg I believe. That's not bad for a mid/full-size car. You can't really do anything to your 617 to increase mileage.

2.5Turbo · #3 11-17-2009, 10:58 PM

Quote:

Originally Posted by Craig

Well you can't compare a 1970s design with a current design, and the VW weighs about half as much. The new CDIs get decent mileage, about 35 mpg I believe. That's not bad for a mid/full-size car. You can't really do anything to your 617 to increase mileage.

I managed to get 38mpg in my dad's 06 CDI. Mostly MPG conscious driving, half with A/C on, half with it off. It's really hard to go for high MPG in a CDI...you just want to mash that pedal

. I bet if I really tried with the A/C off and driving 60 the whole way I could get 40mpg in it.

Ian White · #4 11-18-2009, 12:01 AM

Its the emission laws, a few states in the US have the most stringent air quality standards in the world and apparently importers aren't willing to import cars that are only 40 state legal. Plus the EPA probably has qualms about the argument also...

Scruffyguy1981 · #5 11-18-2009, 01:06 AM

Another issue with our 617's is the pre-combustion chambers. All modern diesels are direct injection which just by the way combustion takes place results in better MPG and power output. The 617 is still a great engine though (wish it had a gear train instead of a timing chain, but what can ya do.)

Merkey · #6 11-18-2009, 01:11 AM

Also the Imperial gallon is bigger than the US gallon....

GregoryV022 · #7 11-18-2009, 01:42 AM

Quote:

Originally Posted by 2.5Turbo

I managed to get 38mpg in my dad's 06 CDI. Mostly MPG conscious driving, half with A/C on, half with it off. It's really hard to go for high MPG in a CDI...you just want to mash that pedal

. I bet if I really tried with the A/C off and driving 60 the whole way I could get 40mpg in it.

i definetly just watched all four parts of that episode. that show is so funny.

you are so right, the CDI will burn, or at least attempt to burn, (stupid traction control) the rear rubbers. i maxed my CDI out at 42MPG. about 55MPH most of the way way from the bay area to LA. at 42MPH though, it just stopped rising at any measurable rate. so i put my foot down.

one thing i noticed is that the cruise control is less economical that a human operator. i guess it can't see the road and act in advance, it can only react. thus it applies a heavy throttle when it detects the car slow down

here are some HIGH mileage cars
http://www.peugeot.co.uk/vehicles/peugeot-car-range/peugeot-308-5door-hatchback/?sc=fuel-fugitives-peugeot-1024_308_5dr

http://www.peugeot.com/en/innovation/engines/hdi-fap-engines.aspx

t walgamuth · #8 11-18-2009, 05:51 AM

YOu can increase mileage very nicely on a 617 by running a higher gear ratio in the rear end and with a five speed od tranny. In my 83 240/300d with euro engine I have a 307 diff and five speed and can get 36 mpg with regularity on the highway.

nhdoc · #9 11-18-2009, 07:52 AM

Quote:

Originally Posted by Merkey

Also the Imperial gallon is bigger than the US gallon....

Yeah, don't forget this...whenever I watch top gear or other Brit shows I always say "how do they get XX MPG out of that" but then remember they are dealing with about an extra quart per gallon!

leathermang · #10 11-18-2009, 09:03 AM

Quote:

Originally Posted by t walgamuth

YOu can increase mileage very nicely on a 617 by running a higher gear ratio in the rear end and with a five speed od tranny. In my 83 240/300d with euro engine I have a 307 diff and five speed and can get 36 mpg with regularity on the highway.

We need an electrically controlled two speed rear end .
This would keep us from having to fight for the last of the five speeds..
and those who can not/will not shift a manual would not be totally left out....
My 1954 Ford 500 stake bed has one.... a little large for any of our cars though.... Some racers had two speed rear ends at one time but I do not remember seeing any which were not manual change ( get under the car and change where the driveshaft connected ).
Anyone have that kind of production capabilities at their house ? You can be a hero in short order and make a bunch of money in the process.

Shawn T. W. · #11 11-18-2009, 09:55 AM

Yeah a two speed rear would be real nice, if somebody is gonna make one, why not just make a SIX speed manual tranny and be done with it?!

okyoureabeast · #12 11-18-2009, 10:01 AM

Quote:

Originally Posted by Shawn T. W.

Yeah a two speed rear would be real nice, if somebody is gonna make one, why not just make a SIX speed manual tranny and be done with it?!

I heard Daimler made one for the Anartic market.

tombance · #13 11-18-2009, 01:24 PM

6 speed manuals are quite common over here.

Scruffyguy1981 · #14 11-18-2009, 02:32 PM

If someone had the funds (I may eventually get to this) You could take the intermediate flange off of the 617, take it to a machine shop withe the bellhousing of a 6 speed (Tremec is popular amongst the Volvo group, high power rating and easy to find in the US) and have a new flange made to bolt it to the engine. I don't know how the clutch and pedals could be worked out (especially with the SD since it never had a stick option). Other than that as long as the shifter lines up in the console the mounting and driveline mod should be easy. Anyone on here have experience adapting tranny's to engines? Love to hear some ideas!

cirrusman · #15 11-18-2009, 02:47 PM

I hadn't thought about the imperial gallon thing... hm, that's true. Making some math I'm sure I'll fell a bit less depressed after watching a Top Gear episode again

About the tranny, I'd LOVE to install a 5-speed tranny in my Benz. The SD never did come with the manual option as scruffyguy1981 pointed out, which is a real shame, but I think that's no issue. I've seen other threads here showing the how-to.
Thanks people!