I bet that pushing a M103 harder with lower ratios would use almost as much fuel as just running a V8.....if not more.

The question is, when the MB engineers set up the 300SE driveline, why did they choose a 3.46 if a lower ratio would have also worked/worked better? They were probably shooting for the advantages of short shifting/avoiding 1st gear in the city to maximize fuel economy. The M103 can get REALLY thirsty when pushed.....I've seen 14mpg in my 300E when driven spirited....and its a lighter/more aerodynamic car than a W126. What kind of mileage does a 300SE even get? My 420SEL (and my dad's) average around 19 city when driven normally.....often better than my 300E gets.

You can presuppose all you wish about why M/B did what they did.

Or, you can look at the final drive ratios that I presented above and make a judgment based upon that data.

Or you can simply render your opinions without any data to support it.

Your choice.

Brian,

The 2 cars that we installed the 2.47/1 ratio diffs did well on the highway, but around here with all of the up/down around town driving were just FLAT low on power.
Constant manual shifting & kickdown.

The 1 car that we installed the 2.88/1 was better all around & even got better mileage that the ones with the 2.47/1.

I would agree completely if the existing 2-3-4 gears are utilized.

However, if I get the valve body modified and use 1-2-3-4, the final drive ratios for the first three gears are SHORTER than stock.

Therefore, I don't see how the vehicle would be flat low on power.

Effectively, with the 2.47, I want to use 1-2-3 for everyday driving rather than the current 2-3-4. Consider the new fourth to be an "overdrive" for highway use only.

All my info & feed-back came from the owners of those cars.
I only drove each several times.

Making the car start in 1st gear is really the key either way.

The 2.88/1 was from a 1985 300DT.

Unless the owners modified the vehicle for FGS, I completely agree with their assessment regarding the 2.47. Anyone who tries to use it with the existing 2-3-4 gears would be foolish.

My entire premise is based on the shorter final drive ratios of 1-2-3 with the 2.47 as compared to 2-3-4 with the 3.46. I'm convinced that the vehicle will drive better than stock and I intend to do it.

Either ratio is better than the 3.46/1 IF most of the driving is highway!!

Good luck, and don't forget the speedo..

Did it have ABS? If not you're going to have trouble putting it in. Plus I thought the whole differential mounting on the GenII W126 was different?

-J

The 2.88 diff and FGS with my M103 feels just about perfect and I get around 26mpg highway.

I read somewhere that Germany (or just MB) had some kind of requirement that a car was required to climb a very steep incline from a standing start.
That was the original reason they installed the low 1st gear, then set the tranny to normally start in 2nd.
In my humble opinion the 300SE came to be when gasd prices started to spike, but more importantly, they knew Lexus was developing a car that considerably undercut their cost. So, they just dropped the 300E engine in the bigger car. They still needed the 2nd gear start and the super low 1st gear for the incline test, so they just geared it where it would take off in 2nd at a reasonable rate and walked away without much engineering effort.

In my mind, they virtually ruined a great car in one fell swoop.
I put off trying to modify mine, thinking next year I'll sell it; been 21 years now of useless over-revving and poor MPG, but she's still going strong for an around town daily driver, and now is an official family member.

DG

21 years is a long time.

How many miles do you have on it, and what issues have you dealt with on the car?

IMHO an OM617 with a 2.47 is a much more doable and livable combo than an M103 and 2.47....there's just no torque at low rev's with the M103. Our now retired (from rust) 300SD is a 2.47 conversion we did ourselves and it drove great, plenty of power off the line with the diesel. Top speed was around 105ish, it ran out of HP at that speed to push the lower ratio diff. 75mph at 2500ish rpm was very nice/quiet. Based on driving my M103 with a 3.07 in a W124.....it barely has enough torque for that setup. :eek: The 420 can glide away with minimal effort in 2nd gear with a 2.47....and can still do 19-20mpg city if you're gentle. And yet still has the massive power when called upon.

617 is ok, M116 and above are excellent. I would bet a M103 + 2.47 will get lower MPG's than a M116 + 2.47.

M103 is best suited to a 5 speed manual in a W124 or W201. With a manual......maybe a W126 too.

You're inability to read and understand final drive ratios is causing your erroneous conclusions.

The M103 has more torque than the OM617.........it just happens at a higher rpm.

The stock M103 uses gears 2-3-4.

The proposed solution with the 2.47 uses gears 1-2-3 for everyday driving and uses fourth as a highway gear.

The available torque to the rear wheels is greater in the proposed setup than the stock setup in all gears with the exception of fourth.

Pat already explained that the highway performance is perfectly adequate with the 2.47.

So, in conclusion, I find your statements without sound engineering judgment and, since it's my thread, I'd prefer if you refrain from posting further on it.

The M103 & M104 engines LOVE RPM! It might not FEEL right to you after driving a diesel, but don't fear the RPM.

What you need to do is a little math. Research and find the torque peak RPM of your engine. Determine the most common speed that you will be running the car. Then calculate for the gear ratio that will put your engine RPM at peak torque. That is the most efficient RPM of the engine.

Larry

Although you might believe that the torque peak is the "most efficient" rpm, you've generated a factually incorrect statement for nearly all driving conditions.

Automobile engines are rarely required to produce peak torque at anytime, with very few exceptions unless you drive like an *******. This specific vehicle will NEVER be required to produce peak torque. Therefore, the discussion of efficiency at peak torque is moot.

Any engine will be most efficient at the slowest possible rpm that will propel the vehicle at the desired acceleration rate. If you could run the M-103 at 1500 rpm and be satisfied with the performance, its efficiency (as measured by the parameter: miles per gallon), would be superior to any calculations made at the magical torque peak.

The reason for this is simple. It takes fuel, and a good amount of it, to run the engine at higher speeds, independent of any output torque. Therefore, the converse is true. The less engine speed utilized, the less fuel consumed by the engine.

The ongoing statements made regarding efficiency at a torque peak are legendary, but, unfortunately, they have no basis in fact for most passenger vehicle operations.