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  #16  
Old 09-23-2013, 08:02 PM
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Yes. Everything was thoroughly tested before and after. Two additional reference vehicles with identical drivetrains have been owned for multiple years. With the 10% ethanol gas we have, in a 5.6 liter M117, low to mid-teens is it.

The 4.2 liter M116 and 5.0 liter M117 engines get measurably better mileage than the 5.6 does. Trust me, I own and have owned up to three 5.6-liter 2.47 vehicles simultaneously -- two of them with low mileage. I know what they get.

If you baby the throttle, put it on cruise control, and drive 60-70 MPH....you can probably get 19 MPG, and perhaps crack 20 MPG with a rabbit's foot on your rear view mirror and with a tailwind. But nearly 100,000 miles of driving a 560SEC, and keeping track of every tank of gas, most of it with a 3.06, tells me that 13-14 MPG is generally what the car delivers on today's gasoline, in mixed and city driving.

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  #17  
Old 09-23-2013, 09:53 PM
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85 300D 4spd+tow+h4
 
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Quote:
Originally Posted by gsxr View Post
A minor change in axle ratio won't cause a major change in fuel economy. I think Gerry has already done the MPG calculations over time and found exactly that. My estimate would be ~10% difference, maybe.

FWIW, 2.88 vs 3.06 is splitting hairs... like, 1-2 tenths of a second 0-60 (or quarter mile) and likely under 1mpg difference in fuel economy.

The lower gearing makes it snappier around town, which is nice if the car is primarily city-driven.

Not sure I entirely agree on that with turbo vehicles and cruising altitudes. Either way the biggest difference is manual over non lockup slush box. I got 34mpg gps verified in my 85 300d once, something I got pretty regularly before I upgraded my pump in the 87.
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  #18  
Old 09-23-2013, 09:59 PM
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Quote:
Originally Posted by gerryvz View Post
From the perspective of a diesel owner, this may well be correct.

However, my 450SEL 6.9 generally got 11-13 MPG, and my 300SEL 6.3 routinely got 8-12 MPG, depending on how many unsuspecting Porsche and Corvette drivers got smoked during that tankful. This was using 100 octane low-lead aviation gas, of course.
Actually, it's from the perspective of someone who realized there was a problem in his Corolla because it was getting >35 MPG on the highway . Either way, I choke at your numbers.

Anyway, let me amend that:
Quote:
...since Gerry's car got such comparatively low mileage...
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  #19  
Old 09-23-2013, 10:31 PM
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I remember driving to the Evergreen Airport in Vancouver, WA (across the river from my home in Portland) to buy 100 octane LL at the piston engine pump there. This was about 10-12 years ago. I was paying $2.50 a gallon at that airport and remember cursing at how expensive that was over and above the $1.50 a gallon I was paying for Chevron Super 92 octane.

I didn't mind the 10 MPG I normally got with the 6.3. When you feel the 434 ft-lbs of torque from that big-block under your butt, it's a feeling that you just never get tired of. It was propelling me to high 1.7 and low 1.8-second 60' times at the drag strip, which is explosive acceleration out of the hole. The best my E500 can do is a high 1.9 second 60' time.

Then there was the time I got pulled over (my first laser stop) by the Oregon State Police coming over the I-205 bridge (Columbia River) , from Washington, past the Portland Airport, racing a BMW E46 M3 at full tilt in the 6.3. The only reason I got stopped and got the ticket was that I was kicking his a$$. He actually had a bit more HP than I did (he had 333, vs. 300 with the 6.3) but I had about 75% more torque than he did

It's a gasser thang.....
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  #20  
Old 09-23-2013, 11:00 PM
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Rather than speculate...

Run a comparison between axle ratios to see where your vehicle speeds are within a given gear, relative to your engine's torque curve.

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  #21  
Old 09-23-2013, 11:13 PM
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It takes a pretty substantial axle ratio change to move an engine far enough out of the optimum efficiency window to make a big change in fuel economy. It also makes a difference if you are talking about pure city, mixed, or pure highway economy; and how much of a lead foot you have.

That said... when you figure out the difference in MPG, also calculate the current cost of fuel per gallon, along with the miles driven per year. I find it comical that many people freak out over MPG when the car in question gets driven under ~10kmi per year. I went through this calculation when we switched out my wife's 300D 2.5T (30mpg average, mixed driving) with an E420 (20mpg average, mixed driving). Even with the massive difference... the 300D got 50% better economy compared to the gas guzzler... the actual DOLLARS PER YEAR difference was far less than expected. With fuel around $4/gal and ~10kmi annually, it was ~$500. Nothing to sneeze at, but having nearly triple the horsepower on tap was worth every penny.

Now if you drive a huge amount of miles per year... say, 30k-50k per year... then every MPG can make a big difference in the wallet. If it was going to cost us a couple thousand dollars extra per year to drive the funner car, we probably wouldn't have done it.

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  #22  
Old 09-23-2013, 11:36 PM
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Quote:
Originally Posted by gerryvz View Post
Are you saying that diesels aren't fun ?!?
Stock OM602 at ~2500 foot elevation... no, not really. Efficient, yes. Fun, not so much.

My tweaked OM603 is MUCH better. Darn close to the E420 around town due to the torque.

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  #23  
Old 09-23-2013, 11:41 PM
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I'se gonna say, them there's fightin' words 'round these parts. You done could get run outta here on a rail for sayin' that....
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  #24  
Old 11-03-2013, 01:58 PM
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Thanks everyone I just got back on the site . I decided am going to sell the car now due to a got laid off. Its halfway through body work. Just needs paint. I really dont have the money to finsh car now. May just list it here.

I have a 1991 560SEL with 2.47s , I get 12to14 mpg city and 18to19 hwy.
Like someone else here said I had a 1984 500SEL that got 24to26 mpg hwy.
I was told it was because of decell shutoff the EHA dumps fuel to cool the cats so it dumps fuel everytime you let off the gas is this right?
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  #25  
Old 11-03-2013, 02:30 PM
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Quote:
Originally Posted by gsxr View Post
It takes a pretty substantial axle ratio change to move an engine far enough out of the optimum efficiency window to make a big change in fuel economy. It also makes a difference if you are talking about pure city, mixed, or pure highway economy; and how much of a lead foot you have.

That said... when you figure out the difference in MPG, also calculate the current cost of fuel per gallon, along with the miles driven per year. I find it comical that many people freak out over MPG when the car in question gets driven under ~10kmi per year. I went through this calculation when we switched out my wife's 300D 2.5T (30mpg average, mixed driving) with an E420 (20mpg average, mixed driving). Even with the massive difference... the 300D got 50% better economy compared to the gas guzzler... the actual DOLLARS PER YEAR difference was far less than expected. With fuel around $4/gal and ~10kmi annually, it was ~$500. Nothing to sneeze at, but having nearly triple the horsepower on tap was worth every penny.

Now if you drive a huge amount of miles per year... say, 30k-50k per year... then every MPG can make a big difference in the wallet. If it was going to cost us a couple thousand dollars extra per year to drive the funner car, we probably wouldn't have done it.

For me, never having to deal with smog check or any sort of inspection in California was the main reason to switch from a gasser to a diesel. I had no desire to own a diesel until last year when smog check became an even bigger pain in the ass for old pre OBD2 cars. Going from 15c/mile to 9.7c/mile was just icing on the cake. I drive ~15k miles a year.
Quote:
Originally Posted by partsman225 View Post
Thanks everyone I just got back on the site . I decided am going to sell the car now due to a got laid off. Its halfway through body work. Just needs paint. I really dont have the money to finsh car now. May just list it here.

I have a 1991 560SEL with 2.47s , I get 12to14 mpg city and 18to19 hwy.
Like someone else here said I had a 1984 500SEL that got 24to26 mpg hwy.
I was told it was because of decell shutoff the EHA dumps fuel to cool the cats so it dumps fuel everytime you let off the gas is this right?
I doubt that. You would be spewing massive amounts of unburned HC if that were true.
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  #26  
Old 11-03-2013, 03:57 PM
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Originally Posted by tjts1 View Post
For me, never having to deal with smog check or any sort of inspection in California was the main reason to switch from a gasser to a diesel. I had no desire to own a diesel until last year when smog check became an even bigger pain in the ass for old pre OBD2 cars. Going from 15c/mile to 9.7c/mile was just icing on the cake. I drive ~15k miles a year.

I doubt that. You would be spewing massive amounts of unburned HC if that were true.
That what a bosch fuel dist. Rebuilder told me?
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  #27  
Old 11-03-2013, 04:10 PM
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Originally Posted by partsman225 View Post
That what a bosch fuel dist. Rebuilder told me?
Every Kjet/KEjet/CIS system I've worked on shuts off fuel on overrun EXCEPT during cold start where it will keep the cold start valve on overrun during the first 30-60 sec after a cold start. When the engine is at operating temp, theres a 2 second delay between the moment the throttle switch is closed on overrun and injectors are shut off. Thats not going to impact fuel economy in any meaning full way.
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  #28  
Old 11-03-2013, 05:32 PM
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Quote:
Originally Posted by partsman225 View Post
I was told it was because of decell shutoff the EHA dumps fuel to cool the cats so it dumps fuel everytime you let off the gas is this right?
Doesn't the cat turn excess fuel into heat?

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  #29  
Old 11-20-2013, 12:03 AM
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All I know is my CIS 84sel euro with my same 5.6 motor with 2.47s got 24 mpg. Now that its CIS E it gets less. I know the car is a bit heavier. But lost 5 miles per. Gallon.? Same gears speedo. Where both correct with gps .usen same 300 mile route .?
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  #30  
Old 11-20-2013, 02:38 AM
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Quote:
Originally Posted by partsman225 View Post
Has anyone gained fuel mileage from this swap?
I hàd a 83 300 D I just rebuilt trans. I do have a 3.87 first gear ratio now .not the old 3.68 so I have better take off now I can fell it. Was thinking of the 2.47 swap. It should take off better with my 91 560 gear set. I get 528 miles per tank w no ac on. W ac between 428 460 per tank
What u swappers think? Thanks

Getting 21-24 mpg on avg ac on. All city.never tried hi way as of yet btw
I owned an '83 300D and after 4 years of driving it I decided to swap an '85 diff into it. The results were amazing. The RPMs dropped about 10% and it actually felt like acceleration was smoother, not from a torque aspect it just got up to speed smoother or something, I recall anticipating a loss of acceleration but it never happened. The car used to have a kick in the pants feeling when it shifted from 1st to 2nd, especially if you let up on the accelerator pedal at the right moment and that seemed to increase with the 2.47 gears like it wanted to get up and go! Under full pedal ie. W.O.T. it really didn't lose any acceleration because the torque curve is flat on the diesel and matched up to the differential perfectly at least with a good running engine.

Around town the mileage was not much different but on trips the car took on a whole new character and improved fuel mileage maybe 25MPG at best, with a heavy foot at times and on the new ULS fuel.
I wished I had done the conversion years earlier. Sold the car to buy a 124 Oh well, I really miss that '83 though. Last of the easy cars to work on and super reliable.
DDH

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