# Improving economy **URL:** \ **Category:** General Discussion\ **Created:** [January 24, 2011, 11:19pm UTC](https://community.cartalk.com/t/improving-economy/60430 "2011-01-24T23:19:37Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Sniffles](https://avatars.discourse-cdn.com/v4/letter/s/85f322/32.png) [@Sniffles](https://community.cartalk.com/u/Sniffles)\ **Post date:** [January 24, 2011, 11:19pm UTC](https://community.cartalk.com/t/improving-economy/60430/1 "2011-01-24T23:19:37Z")
While working for an NGO in the medical field in S.E. Asia, I was given a 4 wheel drive vehicle that suited the area. It was formerly a 1961 Mitsubishi jeep built for the U.S. Air Force. It had a small industrial diesel engine fitted into it some time in the distant past. My problem. The gearing for the vehicle was originally for a gas engine that turned 3600 rpms. The diesel engine goes red line at 2700 rpms. When I drive on the highways, I get 40+ miles per gallon provided I drive below 40 miles an hour. At 55 miles an hour I get 15 miles per gallon. I am running the largest tires that can fit on the critter to improve road speed a little. Any thoughts on how I can improve my economy more? ---
**Author:** ![ken\_green](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/ken_green/32/816_2.png) [@ken\_green](https://community.cartalk.com/u/ken_green)\ **Post date:** [January 25, 2011, 12:15am UTC](https://community.cartalk.com/t/improving-economy/60430/2 "2011-01-25T00:15:03Z")
Any room under there for an overdrive unit ? Gear Vendors sells add on overdrives for many applications. Not cheap though at about $3000.00 ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [January 25, 2011, 12:24am UTC](https://community.cartalk.com/t/improving-economy/60430/3 "2011-01-25T00:24:55Z")
Or just replace the transmission with another with more gears. If you can find one that fits. ---
**Author:** ![dagosa](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/dagosa/32/9837_2.png) [@dagosa](https://community.cartalk.com/u/dagosa)\ **Post date:** [January 25, 2011, 3:43am UTC](https://community.cartalk.com/t/improving-economy/60430/4 "2011-01-25T03:43:56Z")
Sounds like a neat car. The cheapest may be to change the rear end gear ratio. Hope you have enough gears in the transmission to otherwise to compensate. Best left to a professional and only if you can find the parts. ---
**Author:** ![Sniffles](https://avatars.discourse-cdn.com/v4/letter/s/85f322/32.png) [@Sniffles](https://community.cartalk.com/u/Sniffles)\ **Post date:** [January 25, 2011, 4:49am UTC](https://community.cartalk.com/t/improving-economy/60430/5 "2011-01-25T04:49:01Z")
The original transmission was replaced with a Mitsubishi improvement over the original jeep. This gave it 4 gears and the ratio is slightly overdrive. Unfortunately, this is the smallest jeep made. After the diesel chewed up about 10 drive shafts a creative mechanic built a drive shaft, sans shaft, to fit in the 14 inches between the back of the transfer case and the rear end. I know that, if I could install and overdrive and run the engine down at 1500 rpms my economy would increase drastically. As for replacing the rear end, finding a matched set of higher speed differentials isn’t likely to happen in Thailand where we roam. I was hoping that someone has already addressed this shortcoming in jeeps and created an aftermarket transfer case that has overdrive. (I’m dreaming, right?)