3.9 V8 Mpg

I have to drive from cornwall to east sussex this weekend a total of 315 miles i've never done a long haul in the V8 and just wondered if anyone had any idea on average mpg. I know it will vary frome enging to engine but i'm just after a ball park figure so i can prepare for the fuel bill

you should get 20ish

in me 3.9 auto rangie i got 25mpg on a run 18 round town

mines pants on petrol. i'm lucky if i get 250 mls to a full tank
although wierdly it uses the same amount of litres per mile on lpg

This could be a bit pricey me thinks gonna be looking at £80ish each way

It'll probably take a tank there and a tank back. My 4.6 managed to just get to Glasgow from where I am, 360 miles.

my figure of 25 comes from chasing lorries at 56 ish and niot much more.

last time i did motorway on LPG in a V8 158 miles it cost me £16.30 at 36p a litre so can you work it out on that.