Diesel Mog mileage

[OS-Aussie]

Ok guys I have a couple of questions...

Who has high speed diff ratios installed and is there a decent mileage increase ?

What kind of speeds did you guys run at on the freeways / highways in the US ?

What appears to be the optimum freeway speed, not just mileage, but also noise and safety feel ?

[oonimog]

You didn't mention which model you're interested in but here's my experience:

I have high speed diffs and a 170hp 352A (turbo) in my U1300L37. On 14.5's (365/80) it cruises comfortably at 100kph and consumes about 19-20L/100k. It's only ever had the high speed axles so I have no personal experience on the mileage difference between standard and high speed axles. But, during a long trip taken with a friend who's U1200 has standard axles, he used a fair bit more fuel than I did. No surprise given my lower RPMs at the same speed.

As for safety, the truck is quite stable and handles well at 100kph, but I think it's most comfortable at 95k. I'm sure the wheel base helps. I've driven a friend's 1550 with a tweeked OM366LA, high speed axles, Claas overdrive, and 395/85's up at 125-130 kph and things start to get a bit spooky at that speed.

I've spent many long days driving for weeks at a time and noise hasn't really been a problem, but the cab is insulated.

Hope this helps.

[Chas Stricker]

I have a 1250L DoKa with the 352a (turbo). It has the "superfast" axles and at 100kph(62mph) it runs about 2200-2300 rpm. Empty it gets about 11mpg and towing about 9-10mpg. My truck will do 75mph rapped out. It is very stable at that speed yet you feel like you're pushing it (mechanically not stability wise). I don't have alot of insulation yet but it still is quiet enough for my family to travel. Did I happen to mention it can be slow in the passes (35-45mph)? I don't mind because I think slowly also.
Chas

[charlieaarons]

My U500 is not a typical SBU Mog. It has 5.92 gears with an 8 spd with top gear = 0.736, so top gear = 4.36. With 395/85R20s it runs ~1900 rpm @ 60 mph, which is my cruising speed. The motor puts out peak power at 2200. It is governed at 70; I've had it at up to 75 on downgrades. It feels stable and is relatively quiet (can listen to music at any speed) but there's lots of reasons to keep speed limited to 60: mileage (27L/100km with gvw = 12000kg), general road safety, and tires. The tires are "rated" at 70 but it's really a 55 mph tire which has been downrated on load from 168 to 158 (11200kg to 8500kg/axle) in order to uprate the speed. Since my rear axle load fully loaded approaches 8000-8500kg I feel more comfortable at 60.

Charlie

[OS-Aussie]

Claas overdrive, do tell ?

I guess that the 352a is the topic for me but general unimog is good.

I think tires will also impact these questions

[charlieaarons]

Claas overdrive, do tell ?

I guess that the 352a is the topic for me but general unimog is good.

I think tires will also impact these questions

No Claas OD. All UGN and UHNs come with an 8 spd with the same ratio steps as the SBU 8 spd but 0.736 taller, so 1st is 9.57 or thereabouts instead of 13.01. Not really a problem with the two low ranges. Axle gearing varies from 5.92 to 6.94.

Charlie

[oonimog]

The Claas is a ~ 22% OD gear splitter. It allows use of OD in each gear, doubling the number of gears available. You essentially get 1st, 1st x 22% OD...8th, 8th x 22% OD. It's nice because in addition to allowing 22% more speed (assuming you have the power) or 22% less RPMs at the same speed, there are times when a "half" gear is really helpful. The downside is the cost - upwards of $5K (not installed).

The OD replaces the bell housing so it is between the engine and transmission (the two are divorced on an SBU). Nice because installation is easy but it means no engine driven PTO.

[charlieaarons]

The Claas is a ~ 22% OD gear splitter. It allows use of OD in each gear, doubling the number of gears available. You essentially get 1st, 1st x 22% OD...8th, 8th x 22% OD. It's nice because in addition to allowing 22% more speed (assuming you have the power) or 22% less RPMs at the same speed, there are times when a "half" gear is really helpful. The downside is the cost - upwards of $5K (not installed).

The OD replaces the bell housing so it is between the engine and transmission (the two are divorced on an SBU). Nice because installation is easy but it means no engine drive PTO.

If it decreases rpm by 22% the ratio is 0.78:1. If it increases speed by 22% the ratio is 0.82:1. Do you know which it is?

Charlie

[oonimog]

Charlie,
I believe .78 so top gear is 1.00 (transmission) x 5.307 (axle) x .78 (OD) = 4.14

On a different topic, which engine did you drop into your M37, Cummins?

[charlieaarons]

Charlie,
I believe .78 so top gear is 1.00 (transmission) x 5.307 (axle) x .78 (OD) = 4.14

On a different topic, which engine did you drop into your M37, Cummins?

I'll bet you it's 0.82 because 1.22 squared = 1.484 is very close to unimog gear spacing.
My M37 has a 3.7L Hercules.

Charlie