since i had my e34 540 touring converted to gas i have kept a little chart of my mileage,gas useage etc,a bit sad really.
but it helps me to tell when i have a problem

since conversion i have done 342.8 miles

my miles per gallon are 17.57.for a fookin heavy auto tank with near on 300bhp it`s great
a litre of lpg around here is 42.9p,which works out at 3.86 miles per litre.
just like running a family sized car

bet my newer 540 does better though,will have to do the same for that

dave