Gearing is one of the most cost effective ways to squeeze better performance out of a vehicle. Gearing can be optimized for mileage (“tall” gears like a 2.75 axle, or overdrive) or for towing or acceleration (like a “low” 4:11 rear axle). Many vehicles use a medium rear gear kike a 3:73 and overdrive transmission to try to deliver the best of both worlds.

The idea is to keep the engine running in the power band where maximum torque is being produced, and to make sure that when the transmission is shifted that the RPMs do not drop too low in the power band. For woodgas performance, it seems that being able to have two sets of gears could restore acceleration caused by the loss of power when running woodgas.

I remembered reading a car magazine article about a unit that bolts on the tailshaft of the transmission and effectively doubles the number of gears you can use in your vehicle.
I found the manufacturer today and the site has a LOT of published articles and videos covering the basics at

Very cool… I knew something like that was out there from my days in auto parts but hadn’t heard anything from anyone about them lately… good find there Gary

I do like the idea, but find it cost prohibited in my case. Kind of like having an automatic 2 speed rear.


that is what I was looking at a while ago. How come they don’t make 2 speed rear ends anymore?? I couldn’t find any for smaller pickups. Thought that would be a pretty decent thing to do. Anyone know of any smaller rear ends with 2 speeds, new or old?


Hi Anthony, My personal feel is they already have things maxed. How many times did you see me shift into overdrive ? As soon as I would get in it there was some truck pulling out or we hit the next town. Imagine that gasifier trailer on your car. That’s what I built it for. We would have been seriously cruising but unable to carry the weight of much wood. Those 3800 engines were made for woodgas. Of course I don’t go on many trips more than 10 miles each way so it can handle that. 150 round trip is no problem either. Further is possible as who needs a rear seat ?? Busy with survey work and life here … Got a rain break today so it is office time … Mike L