So I finally got my Doug Nash overdrive installed along with the new speedo gear etc. The vehicle is a 1988 E250 with a c6 and 3.54 gears.

My first impression is that I really like it and that it makes it much easier (almost too easy) to cruise at higher speeds on the hwy. I put a total of 318 miles on it with about 80% of it being hwy. Mileage was 14.9mpg. This is on the upper end of the mileage I would get for the same route prior to the install (I would range between 14-15mpg). However, instead of having the cruise set at 60-63mph I set the cruise at 73mph. Wind resistance has a big effect on mileage of my van since it has the aero of a barn. With that in mind I think slowing down to about 65mph should show some pretty good gains.....maybe a couple of mpg.

Flatter terrain would help too. I took a road trip into Ohio a few weeks ago (to pick up the DNE2) and was able to get a little over 16mpg with the cruise set at 65mph. Thinking the overdrive I would have been able to hit about 18mpg.....if I can get in that range I will be happy.

All the temp gauges seemed to run a little lower.....EGT, Trans and Coolant.

Acceleration, while noticeably slower, isn't too bad and the O/D can always be turned off with the push of a button. I am also thinking it will help if I am towing anything a little heavier since I will have a 2.5 gear available.

The real test with be in 2 weeks when we head out on a 2000 mile trip.
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I think you're going to find that unit's not going to pay for itself. My 96's GT40 headed roller 351 gets about the same mileage, with the E4OD and 3.55 rear (shod with 28" tall tires) Mileage was actually a little better in the mountains with the slower speeds (less than 65 mph) you use a little more on the uphills but use nothing to speak of on the downgrades. Mileage going across Texas was the same going as it was coming back, and that's with a 5,000 ft difference in elevation in 650 miles. (12-12.5 @ 75 mph)

 

You could be right, though I have spoken with a couple people that have done a before and after comparison on the same basic vehicle as mine (same make/model/engine/trans) and they saw a 2-3mpg increase. Of course there are a lot of other factors that can affect it such as the terrain, elevation, driving style etc. The drop in RPM gets me a lot closer to my 1800rpm torque peak.

Doing the math shows that if I can increase the mpg by 2 it will pay for itself in about a year.....but even if that doesn't happen it is worth it to me. It reduces the engine noise dramatically and reduces travel time by increasing the possible cruising speed. Since this is a family road-trip vehicle it makes it more pleasant.

 

... just ask any Prius owner - it is not always about the $$ payback

 

Yea, just don't go looking for the owners of the first gen Prius'. Those have curiously disappeared from the highways. And being married to one of the 1st gen owners, I know the reason why those cars are no longer on the road. We now own a Ford C-Max because of that 1st gen prius.

 

My brother bought a C-Max in Jan of 2013. He loves it.

 

Whether something pays for itself in some time frame isn't the only consideration made when we purchase/install something. I can see a potential big benefit to Doug's products even back when they were first introduced all those years ago.

Being able to even slightly change the final drive ratio when its needed or wanted more than justifies the cost, at least to me. If making the ride more comfortable is a by-product of this installation then it once again proves it was worth it even if "worth" isn't just in dollars.

 

Yea, I hated that 1st gen Prius. Was nothing more than a golf cart with A/C (that shut off as you sat at a red light) Love the C-Max, this things Scoots when you nail the go pedal ! Better mileage than the 1st gen Prius too.

 

You sure you did the math right ? I calculated at 12,000 miles a year and 13 vs 15 mpg (and that's a stretch as it would have to be 100% highway miles) at $3.50 per gal that only adds up to a $430 savings. How much did the unit cost you, both the purchase price and the install costs ? I've never priced the DN unit but the only other I can think off costs $2000-3000.

 

I got the DNE2 unit used for $550. Shortening the drive shaft was $200. Miscellaneous supplies $50. Grand total for unit and install was about $800. The new Gearvendor units are in the $2-3k range you mentioned.

For the fuel calculation I looked at my log. I drove 3329 in July, 2178 in August and 767 so far this month. The 787 is not counting the current tank or the trip to Flordia (2k miles round trip). I don't have the rest of my log with me, but averaging the 2 months gives me an average of 2753.3 miles a month and 33042 a year. At 13 mpg it would take 2541.69 gallons and at 15mpg it would take 2202.8 gallons. A difference of 338.89 gallons. At $3.50 a gallon that is a savings of $1186.12. Of course miles driven month to month will vary some and so will fuel costs, but over the course of the next 200K miles it should more than pay for itself if I see a 2mpg increase.

Though even if mileage stays pretty much the same $800 is worth the other benefits that it provides me with. Less drive time, interior comfort due to reduced noise and added gears for towing if needed. $2-3k for a new GV Overdrive would not be worth it to me.

 

Ok, yea, that changes things completely. With the expense of a Gearvendor unit, you would have to drive a lot more and for a longer period of time. That's where I thought you were initially. You did right in the swap.

 

Sounds like you made a good move

 

Hopefully I will have a good result to report back in a few weeks.

The new Gear Vendor units are nice. I spent a lot of time on their website drooling, but I couldn't convince myself to spend the $$. Spent some time looking for used ones, but used most of them were still in the $1500 range. The Gear Vendors require less driver interaction to work. They are like a 2 speed automatic that you just turn on and it shifts itself (though it does have a manual mode). It uses ATF fluid pressure etc to shift. The DNE2 is manual 2 speed trans, so it required the driver to shift it via a push button that engages or disengages it.