When trying to improve the fuel efficiency of a Series Landrover, you need to look at how current production cars have improved fuel economy. Only a few of these can be applied to a Series Landrover.
1. Change to diesel - pretty well covered above. But apart from the cost, there is the problem of matching gearing, and finding a suitable engine.
2. Improve combustion efficiency of the petrol engine. Some room for improvement in the standard engine, but not really feasible to follow the route of modern petrol engines with an ecu holding ignition timing, mixture and boost right on the edge of preignition all the time, so you are never going to do anywhere near that.
3. Reduce aerodynamic drag - lots of scope there, but anything significant and what you end up with is not a Series any more.
4. Reduce mechanical drag - smaller diameter, narrower bearings throughout, low friction seals, disc brakes everywhere, remove unnecessary bearings such as full floating hubs. Not much of this is feasible.
5. Reduce mass. Apart from dumping the junk in the back, not a lot can be done about this once past the design stage.
Let's face it - fuel economy was not a design criterion for the original Landrover, and only modest improvements are really feasible. The only really practical one is conversion to diesel, and unless you are doing a lot of mileage, you will never recoup the cost even of this. The other thing that can be done is LPG conversion, which will not improve the economy, but will reduce the cost.
John
