Improving 617 fuel efficiency through modification..? - PeachParts Mercedes-Benz Forum

johnd · #1 07-21-2006, 08:06 PM

Most all the threads on the boards about improving fuel efficiency deal with fixing common problems so as to bring the engine nearer to stock efficiency (fuel filters, injector lines, empty trunk, etc.), but what about modifications to attempt to surpass stock efficiency?

I read about switching out the rear differential and using taller tires inflated to higher pressure, but what about things like intake/exhaust modification? All threads on these mods are concerned with improving power/performance, but do straight-fed cone style "cold air" intakes, air-to-air intercoolers, water/methanol injection, straight pipes, or no pipes improve efficiency?

rchase · #2 07-21-2006, 09:44 PM

Hmmm,

You could remove your interior and other accessories such as power steering pump and A/C compressor to reduce weight. Might be a bit conterproductive to comfort.

If you want better performance there are a lot of other cars in the marketplace that don't require oddball modifications.

jbach36 · #3 07-21-2006, 10:00 PM

I dunno, seems like if you have to spend the time to figure out how to do really hard things like changing the differential or the exhaust stuff, better to get a 2nd job that pays more to buy the fuel, or to carpool once in a while. That all seems like a lot of work to change that stuff out. Best solution yet, convert to biodiesel or WVO, get fuel for next to free by the time it's done, and your car will be permanently converted.

Brian Carlton · #4 07-21-2006, 10:14 PM

Here's the last five tanks in the SD:

30.47
28.89
31.47
30.28
28.69

All the driving is 90% highway. Some of the trips had a/c for part of the run.

How did I get it?

A few simple things:

Speed between 62 and 70 depending on conditions. Usually 68 is preferred (by me........not by the 617.........it would prefer 55 if fuel economy was paramount).

Tire pressure at 34 psi.

Power Service...........6 oz. per 15 gallons

Allowing the speed to fall rather than mash the rack to hold speed on steep upgrades.

Boost at 13.5 psi max.

No EGR

A few more difficult things:

New valves.

2.88:1 diff.

Precise IP timing...........15°ATDC with the electronic RIV tool.

I'm quite sure that I can get additional MPG, but, at what cost? Could I ever recover the funds if I choose some exotic intake modifications? Almost assuredly, I can't.

My only additional thought is to lower the front end slightly and take advantage of a slightly improved Cd. Anything else is simply not cost-effective. This vehicle is never going to achieve 35 mpg unless I drive it at 50 mph.

And, BTW, the odometer is accurate to within .1% so you can forget any inaccuracy on that issue.............

mespe · #5 07-21-2006, 10:19 PM

Why not just drive the car downhill all the time?

Brian Carlton · #6 07-21-2006, 10:21 PM

Quote:

Originally Posted by mespe

Why not just drive the car downhill all the time?

Can you do that?

83-240D · #7 07-21-2006, 10:23 PM

brian,

let me see, this car is 22 yrs old and has better hwy mileage than many 4 cyl economy cars made today? and that isn't good enough? your car is bigger and has more room than many of those cars and it is a BENZ!!

give it up man!

last weekend i got 27 in the td with three windows open and the sun roof cracked on a 90 deg night. no a/c. i have heard the windows drag so i hope to get it done soon.

Brian Carlton · #8 07-21-2006, 10:38 PM

Quote:

Originally Posted by 83-240D

brian,

let me see, this car is 22 yrs old and has better hwy mileage than many 4 cyl economy cars made today? and that isn't good enough? your car is bigger and has more room than many of those cars and it is a BENZ!!

give it up man!

You misunderstood my statements. I've invested far too much money in the SD and I'm extraordinarily pleased with the fuel economy. I'll not spend any additional money in an attempt to get .5 mpg. If I choose to lower the front end, it will cost nothing...........and simply take about three hours with the spring compressor. I'd probably do it for improving the lines of the vehicle more than the fuel economy. As you probably know, an SD has a slightly nose high appearance that is a bit undesirable.

pawoSD · #9 07-22-2006, 02:12 AM

Lately I switched from taking the freeway route to lansing, MI, to the "old route" which is a 55mph state road, the overall distance on that road is 10.3 miles less, plus, at 55mph, my mileage is into the sky. On my latest fillup (today) I filled up at 300 miles....130 of those were at 80mph on the freeway (before I switched routes) after I switched I did the other 170 miles at 55-60mph on the new route....my mileage just from that switchover? 27.7 mpg!! Thats up from a usual 23ish! I have now driven 91 miles on my latest fillup (all on that route) and my needle is still solidly pegged at full tank! I am expecting about 30-32mpg's by making this change. Sure the drive is a bit longer (an extra 20 mins each way or so) but its more relaxing, more too look at, and saves a ton of $$ over freeway driving. I'll know by the end of next week what my mileage has gotten up to....

Point of story, the 617 is plenty efficient, these are 4000+ lb cars, getting over 20mpg in them is impressive, getting 30+ is incredible. Changing the driving habbits can have a much greater effect than modding the car. There's a mathematical limit to what that engine/weight/consumption is going to be per given speed.

Matt SD300 · #10 07-22-2006, 02:32 AM

LOL

My benz gets the the equivalent of about 125 mpg!! (cost per mile)

Yep....still running a WVO blend 15/85 ..RUG/WVO ...ok 10/90 now summer.

13,000 miles later & Cummins has 23,000 miles on the heated blend. Both are running great!