LPG Not as good as promised

I have a p38 4.0 running on LPG it has a decent multipoint system with a 80L spare wheel tank, only seems to hold bout 60L tho. The car is all serviced as is the LPG system, anyway the guy the owned the car berfore was talking around 200-250 miles per £30 of LPG but i get nothing like that 150-170 and that at the dia most, I do realise it could be due to the way i drive, not stupid but not defensive either but 100 miles less than he was getting per tank seems alot does anyone else have one of these running lpg and if so what milage do you get.
Fanks Tim

I'm running a 3.9 classic on LPG. 70L (water capacity) tank, so about 53L (net gas capacity) actual useable LPG gas. My mileage is between 140 - 160. So, yours sounds about right. However, I would think 200 at least is achieveable at 60mph on motorway.

I believed the guy who previously owned your car over quote you on the desired mileage rather than the achieved mileage.....

I believed the guy who previously owned your car over quote you on the desired mileage rather than the achieved mileage.....[/quote]

Or he drove like an old woman lol! , but seriously thanks mate mind at rest now i guess mines fine, although one more question if you dont mind, does yours loose any power on gas? mine doesn't really loose power as such but you can definaltly notice something is missing on lpg its all a little.. well flatter i suppose. I do still get the same overall performance i would say, but just seems like the old girl prefers petrol is this the same fo you?

On LPG, it does run a little 'flat', losing a tad on the ommph effect. The engine seems to be slightly less responsive, but thats alright looking at the savings on fuel costs...lol....

However, the effect will be more obvious or significant when towing uphill. By switching to petrol before the hill while towing, I could go up without needing to down shift to 4th or even 3rd. Just have to remember to switch back to LPG after....hehe...

LPG burns slower than petrol, so in an ideal world you need a lot more ignition advance, but the standard ECU can't optimise for LPG as detonation would occur when running on petrol.

If you've got the money RPI Engineering do replacement ECU's that have 2 settings, but they are a little pricey "RPi Engineering - Specialised Rover Engines"

Lovely looking 16i by the way.

Hi Guys, just joined this group, very timely too as I have recently acquired a 3.9 auto 4 speed with underfloor gas but haven't had chance to test it out yet. However I'm of to france in it soon and your comments are interesting. I've found it goes nicely under normal driving but if you kick down the box on gas it just stands still! flick over to petrol and boom off it goes like a rocket. Is this to be expected or do I need something looked at? Any other comments on this input would be appreciated. Sorry to hijack your thread riddler.

What do you mean by stand still?? While on LPG, the performance should only be marginally less responsive than on petrol. I am not 100% sure on the injection system on LPG, but am suspecting that it does not provide the high flow needed while on kick down.