Now that I have put a few thousand miles on the 2.47:1, I can say that it is a little bit high for the average 617 and other folks who have suggested a 2.88:1 seem to be spot on, IMHO anyways.

While we did not net the 4-5 mpg increase in mileage we had hoped for (during this experiment) we were able to maintain our average fuel economy of 25-28 mpg (and sometimes 30 mpg but not consistently) while increasing the cruise speed from 55-60 to 75-80 mph.

Over the past 20 tankfuls, mileage numbers have been consistent, with calculations altered for the 7.29% speedometer error.

It's a great gear on the highway.

I've recently driven from California to Texas a couple of times and drove the W116 for test purposes and trunk space. On the first leg of that trip I drove non-stop 75-85 (where I could do so safely) with the A/C on and got a full 610 miles on 19.5 gallons, for about 31.2 mpg.

The hills do slow the car down, but it will climb the 'Grapevine' in 4th gear at 70 mph at a little bit off the kickdown switch and I have never had to kick it down into 3rd.

Driving up into Big Bear, California is another story. There are sections where the grade is as steep as 16% in some sections and climbs several thousand feet. That climb involves a lot of downshifts and WOT.

It's a great highway gear to be certain, but as other have posted, I think the 2.88:1 is about as far as one should go.

Hope this helps...

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership