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

 

If you are friendly with any farmers particualrly poultry ones, most use LPG to heat the sheds in winter, so you could be paying as little as 11p a litre!!, it is the same gas but without the stench agent(smelly perfume) that has to be in road gas.
Do you have a spark advance unit ?
tabetha

 

If your using a multi point kit just make sure you have good filters in if your going to go using farmers lpg

Spark advance untis is still somethign I need to play with Tabetha, not that my Cavalier is going to gain much power

 

34p a littre near me on an industrial estate, for road use, shame my car aint lpg, would be handy at 17.1mpg avg

 

LPG rocks!! Me rangey has it. 39.9p a litre at Asda round the corner. Full tank is just over £20 and lasts me about 160 miles if I don't kick its head in.

 

enlighten me tabetha,whats a spark advance unit?

i run a zavoli sequential system,if that helps

dave

 

It does what it says on the tin, it advances the ignition, fools the cars lpg ecu into thinking all is well and normal, but you can preset the advance amount over an dabove that normally offered by the lpg ecu/car ecu.
I ran a total of 58 degrees on my xr4i, the difference was night and day, in smoothness and power, suprisingly economy only bettered very slightly, but power was up big time.
On the rollers it made an extra 28lb ft at 1200rpm lower, but 22bhp extra at same rpm.
I used a WOLF 3N box of tricks, adjustable in 4 degree increments, you adjust it/advancing until it does not get any better then stop.
tabetha

 

but that 17.1 mpg is with lpg prices,converted into petrol prices it is 39.9mpg.

so running a big v8 auto on gas is the same as most family run arounds

 

so what kinda ratio of gas to petrol consumption do you see? Prices differ everywhere, but if you had a car which did 20mpg on petrol what might you expect to see on gas?

 

when i fill the gas tank up i also put a £10 of petrol in,fuel tank is 90 litre and i ain`t filled it yet althought it`s getting there

from stone cold it turns to lpg after about 1.5 miles then runs solely on lpg.so i don`t use must petrol at all
when it`s warm it changes over almost straight away.

concerning your 20mpg on petrol,haven`t a clue mate,sorry
it`s all down to how you drive it,auto/manual,do you do town driving or motorway.

i have a mixed route really,town,dual cabbage ways and motorways.

it is only the really ideal way to run a big engined car

hope this helps

dave

 

20mpg petrol will normally see around 17mpg lpg, but can be as high as 24/25 with advance.
LPG can be used from stone cold first start perfectly, even from -25C if set up right, some have the fuel tanks removed as well.
tabetha