I just heard of someone removing the front propshart on their 4x4 to improve MPG and was wondering what gain they would really get if any?
What do you think?

Assuming you're driving a 90, with permanent 4WD, if you remove the front prop shaft you're not going to be going far unless you lock up the centre diff (otherwise all the power will go to the front as that is the route of least resistance). Not a good idea.

If you have a series motor with part time 4WD and no centre diff, you might save a bit, but nothing that worthwhile as the only bit of mass you are saving spinning is the short front prop shaft.

With a Series you would be much better off fitting freewheeling front hubs, at least you can then choose to switch to 4WD when you need to.

Karl.

Perhaps a very small gain is possible, but I doubt it amounts to much. The front axle internals will still be spinning, so those losses won't be reduced unless there are free wheeling hubs too. Even then, I wouldn't think there was a huge gain. The downside is that all the power goes through the rear axle, which might be ok on a low output engine, but I wouldn't like to do it on a V8