W108/109 4.5 gas mileage

[Frank Reiner]

Originally Posted by alabbasi

I'm speechless

An assertion that is totally without merit. Pity.

[Graham]

Originally Posted by alabbasi

4.5 fuel mileage sucks but adding an extra gear won't help as the 3 speed is more like a 2nd, 3rd and 4th gear. This is why the 1-2 shift happens at around 60mph.

My 72 350SL has same or similar transmission, I believe. W3A 040. However, the 107 is designated as 722.004 and the 108/109 as 722.000. Don't know what the difference is?

I have no horse in this race, but interested in why you say the 1-2 shift takes place at around 60mph. Maybe 40mph at full throttle?

MB 1972 Tech Data Book does give shift points for these transmissions (both 107 and 108/9):

[alabbasi]

Originally Posted by Graham

I have no horse in this race, but interested in why you say the 1-2 shift takes place at around 60mph. Maybe 40mph at full throttle?

NP, the markers are on the cluster give you a good indicator that the first gear ratio is pretty tall on the 722.0:

Here's one from a 450SL



See that it's roughly about the same spot as the 2-3 point on a 380SL with a 722.3



The closest you can get to apples to apples is the 107026 cars. I owned a 450SLC 5.0 and a 500SLC at the same time. Both used the exact same rear end ratio, but the 500SLC used a 722.3 instead of a 722.0 in the 450SLC 5.0, and hence the driving characteristic was pretty much the same.

Why? The 722.3 on the V8 cars would start in 2nd gear unless you mashed the pedal from a stand still and both gearboxes use a 1:1 final drive ratio.

Unless you change the rear end to something else or used an overdrive gearbox like a 722.6 or GM 700/R4, you'll be turning the same RPM at highway speeds.

Also a quick look on Wikipedia

First gear ratio on a 722.0 is 2.3061
Second gear ratio on 722.3 is 2.4123

They're not that far off. Let me know if I have not understood this correctly. Thanks

[Graham]

Originally Posted by alabbasi

They're not that far off. Let me know if I have not understood this correctly. Thanks

You previously said the 1-2 shift point was at 60mph. But according to Mercedes TDM that I posted above, that is not correct. There is no way the first shift is at 60mph and the second at 92mph.

Those hash marks on the speedo are not the shift points. They are apparently the maximum speed you should drive in that gear. Which would of course relate to maximum engine rpm.

Not all cars had those marks. Some also had a tach with the maximum rpm shown. I didn't bother, but I suspect you could back-calculate those hash mark maximum speeds using max rpms and the gear ratios (2.3 & 1.46 & 1 on the W3A040)

Anyway, just something of interest to discuss on a stormy night in Canada! Just had a tree come down. Luckily hit our shed roof before it gently hit the hood of our E320. No damage, just a lot of cleanup.

[alabbasi]

Originally Posted by Graham

Those hash marks on the speedo are not the shift points. They are apparently the maximum speed you should drive in that gear. Which would of course relate to maximum engine rpm

Right, needless to say the point I was making is that the 722.0 is more like a 2,3,4 in relation to the 722.3. In drive, they will both change before redline.

[auriga]

Originally Posted by alabbasi

NP, the markers are on the cluster give you a good indicator that the first gear ratio is pretty tall on the 722.0:

Here's one from a 450SL



See that it's roughly about the same spot as the 2-3 point on a 380SL with a 722.3



The closest you can get to apples to apples is the 107026 cars. I owned a 450SLC 5.0 and a 500SLC at the same time. Both used the exact same rear end ratio, but the 500SLC used a 722.3 instead of a 722.0 in the 450SLC 5.0, and hence the driving characteristic was pretty much the same.

Why? The 722.3 on the V8 cars would start in 2nd gear unless you mashed the pedal from a stand still and both gearboxes use a 1:1 final drive ratio.

Unless you change the rear end to something else or used an overdrive gearbox like a 722.6 or GM 700/R4, you'll be turning the same RPM at highway speeds.

Also a quick look on Wikipedia

First gear ratio on a 722.0 is 2.3061
Second gear ratio on 722.3 is 2.4123

They're not that far off. Let me know if I have not understood this correctly. Thanks

Does 722.6 or GM 700R4 a good fit onto the original beel housing? Or there are some kit can purchased for the job? It sounds like a good thing if it have an overdrive.

[alabbasi]

There's no kit for a 722.6, although some people have mated it to a later M117 engine and used a stand alone controller. I know a guy who mated an om606 to a 722.6 and it transformed the car.

There are kits available to mate an OM617 to a 700R4 which is sold by 4x4 guys. It'll probably mate to a 6 cylinder car. I'm not sure about a V8. The easiest option would be to source a rear end from a 6.3. It won't be the cheapest though.

[auriga]

Im always thinking, some unit like a Overdrive gear box, like the one on early Jaguar saloon manual car, they works like a dream, if them can standalone between the driveshaft. But i can be totally wrong..

[Frank Reiner]

The high fuel consumption of the early M117 is due:
10% to short gearing,
&
90% to thermodynamics.

The specific consumption is high, changing the gearing does not change BSFC. Pounds of Fuel per Horsepower-Hour.

[TZ_280SEL]

I just got back from a quick trip to Washington DC. Hadn’t checked my mileage in a while. I drove 275 miles. Probably 50 were in town (city), 50 were stop and go on I-95 getting to/from DC and the balance we’re doing 75-80 on the interstate.
16.9 mpg. I’m happy with that. Keep in mind I believe the W108 has lower gearing than the R107

[alabbasi]

Originally Posted by Frank Reiner

The specific consumption is high, changing the gearing does not change BSFC. Pounds of Fuel per Horsepower-Hour.

It's already been stated that a modern fuel injection system will likely improve fuel mileage, and get even better results with better gearing at highway speeds. A 90's Buck Roadmaster with a 5.7l V8 will turn ~1900RPM at 70MPH and get 28MPG on the highway.

Not that any of this matters as the least expensive part of owning these cars is the fuel.

[Frank Reiner]

Originally Posted by alabbasi

~1900RPM at 70MPH and get 28MPG on the highway.

And there it is; a significant improvement in thermodynamics.
The engine is a torque-tuned LT1 SBC, with lean-burn mixture feedback, knock sensing and continuously variable ignition timing.

[Idle]

About those shift marks....

VW used to have these on the Bug. I remember asking a salesperson about them and was told they were suggested shift marks. Remember: At this time all VWs had manual transmissions. They were just a cheap sort of tach.

This must be a German thing since I never knew anyone who didn't shift based on the sounds of the engine and the feeling of running out of steam and needing to shift.

[alabbasi]

It's an indicator of where the gears max out and like you said, unless you're drag racing, you're going to shift much sooner. My old Saab had a light which was super annoying.