After 20 years of playing with the 1-2 shift from time to time, I can attest that under the most common use of 1st gear, when you hammer the throttle a bit too much and it jumps down into 1st by itself, the following 1-2 shift is quite harsh. But, you're on the throttle pretty hard in this scenario, otherwise it wouldn't have shifted down automatically. However, if you place it in 1st at a red light, then just drive away normally, the 1-2 shift is quite liveable. So, that should not be a concern in real daily driving situations with a properly adjusted tranny.

But, if you gear it up and lose the occasional stump-puller 1st gear, better not drive around too much in Colorado. I've been in situations where the car would JUST NOT PULL up a pretty steep incline in 2nd, and had to go to 1st to just get it up the hill.

So far, in my opinion, I've not seen any real valid reason not to press on.
Of course, when you do it, then you will have to come to Dallas and help me modify 'Ol Pearl.

Oh, torque peaks and such - I was reading an engineering article on the C5 Vette, and they were explaining how a 400 HP engine can get 30 MPH.
The trick was to operate the engine at the lowest RPM possible without lugging, using the widest throttle opening. This reduces the pumping losses associated with pulling all that vacuum thru a barely-cracked throttle, and it minimizes the rotating friction. Of course, defining 'lugging point" is a bit more complex - the engine must be capable of running efficiently at the desired RPM, partly a function of cam timing and intake/exhaust port tuning. Maybe the 103 engine would not be happy at 2100 RPM at 60 MPH, but I bet it would be fine, it just might want to shift to 3rd when fighting a 2 MPH headwind, Ha! but, my V6 Caddy SRX does that, so I'm used to downshifts when pulling a 0.00001 degree incline.

Do it, i want to see how it works out!

DG

Thanks DG for an informative post.

You raise a valid point regarding the loss of the very low first gear. Without this capability, I am quite sure I could get into trouble with this vehicle in San Francisco with an attempt to start on a hill. The engine can't get into it's powerband due to the limitations of the torque converter and the 2.47 diff. So, I'll avoid going there for the time being.........

Absolutely correct regarding running the engine slower with more throttle. Less pumping losses and less engine friction equal significantly greater fuel economy...........my ultimate goal on the highway. The M103 will be turning about 2400 rpm at 65 mph..........clearly not lugging it in any way.

I will do it..........and will post my results here when completed.

Its like a 10 speed bike,10th gear needs more torque.A v8 would pull 5th with a 247 rear,but not a 6.Now diesels have torque you see diesels pulling a 247.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

All depends what you refer to as "pulling". If I need to "pull" a 7% grade at 75 mph, you might be correct. However, I've got third gear for that.........slightly shorter than the current fourth gear with the 3.46. Puts the engine very close to it's torque peak at 3800 rpm.

Again, an understanding of final drive gearing, explained in the OP is necessary for the discussion.

My analogy is that of a person riding in 10th gear at 50 mph.Still hard to pedal on level ground.Person would need legs of a horse.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

I'm not sure it's a good analogy with respect to the M103. I'm fairly confident it has sufficient torque for moderate grades at 2500 rpm in 4th.

We'll see........

Just out of curiosity, what's the final drive gearing on the S320? What's its engine speed in fifth?

It's Sunday morning, so don't quote me at all on this.
But, "they" say it takes about 25 HP to pull a typical car down the road at 60 MPH. I think Torque = HP x 5200 /RPM (maybe, it's early).
So, at about 2500 RPM, the 103 engine would need about 50 FT-lbs torque to lug the 300SE along a flat road.
We're not talking acceleration or hills or wind; that's the downshift issue we discussed earlier.

DG

Gearing is weird on mine i can do 50 mph in 5th at 1900 rpms the rear end I think is a 3:69.Top end is governed to 130 mph,Euros run 148 mph.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

When I worked at Chrysler.........eons ago..........the figure for a Dodge Diplomat was 15.5 hp @ 55 mph, so the figure for the 126 is probably closer to 20 hp @ 60.

I'm fairly confident that it can produce 40 lb.-ft. at that speed.

Nothing weird about that.

The overdrive is significant.

Goes to show how low you can actually run such an engine and be perfectly satisfied with it. That engine runs at a slower speed than my planned M-103 conversion.



What's the highway fuel economy for it?

Won't having to drop to 3rd all the time in hilly terrain make for high rev/fuel sucking driving, not to mention excess wear on the tranny.....? How much effort does the M103 put into grades with the 3.69 at 75mph? I know that in the W124 it has to work pretty hard on a steeper grade with the 3.07 at 3400rpm at 75mph....they just don't feel like a very torqey engine, the diesels have way more push to give at 2500rpm, and certainly using less fuel. Likely why our 2.47 + 617 conversion worked pretty seamlessly.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Again, you remain confused because of the lack of understanding of the final drive ratios.

With the 3.46 diff, the final drive in fourth is 3.46.

With the 2.47 diff, the final drive in third is 3.55.

I believe we can agree that the difference is negligible. The 2.47 will cause about 50 additional rpm............hardly "fuel sucking".

I suppose you can argue that the downshift causes additional transmission wear if it occurs frequently. I don't expect to need it more than twice in my 300 mile round trip to CT each week. Depending on the capability of the M103 at 2400 rpm, I might not need it at all.

I'd have to say the M116 has more real world capability at 1600rpm than the M103 does at 2400rpm. The M103 is a rev-rocket, not a torque pusher like the diesels and V8's.

I suppose my main question of the project is why go through all the work to end up with a slow version of a 420? A 420 on cruise at 75 can easily exceed 22mpg....and isn't straining to push the car along at 2600rpm, plus, when called upon, it accelerates with un-ending power.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The vehicle is in remarkably good condition with low miles. I intend to keep it a long time.

I don't enjoy the poorly designed gearing from the factory and am convinced that I can obtain 24 mpg for highway fuel economy at 65 mph once I perform the modifications.

Your characterization of "straining" is simply not a factual conclusion.

I think this is a great project and am looking forward to your progress. I just can't believe you're the first person to do this.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".