I have a X308 V8 on gas with a small tank, and because of the way the system works my tank can only hold about 30 Litres giving me a range of about 110 miles. (probably the same size as yours I would imagine) In my case though my nearest filling station is only 2 miles from home and I don't go on long journeys these days so its not really an issue. I suppose I would like a bigger tank but for the moment I can't justify the cost in changing.