14mpg sounds about right. Depends how you drive it etc but, being a Land-Rover and a V8 you're not going to be getting perfect economy! I think you are running on twin SUs? You could possibly get slightly better by fitting a hotwire injection system, improved torque, power, throttle response etc. Thats petrol side though.
Rover V8s run well on LPG, there are a lot of LPG conversions out there & it depends how you do it. Good thing about LPG is that its cheaper than petrol! Yay! So if you do some basic maths you can work out what the equivalent mpg is for petrol. So getting 12mpg on LPG might be like getting (depending on prices) say 23mpg on petrol. Which is a lot nicer for your wallet!
There are loads of different conversions, be careful though your insurer may want to see a certificate for it or something. You could get a second hand one, be careful & fit it yourself. This will probably have a tank that goes in the back, you can get sill tanks that go under the body each side of the chassis rails... Loads of options.
If you are going to get LPG then the basic system is: Tank -> Vapouriser -> mixer ring(s). Which what happens is the air rushing past sucks a reasonably correct amount of gas into the air stream and then all the normal things happen. Suck, squeeze, bang, blow.
An improvement on the mixer rings is a BLOS carburettor. I don't own one (yet! its on the list and I will be getting one!), but from what has been said about them, you're not going to get much better unless you go for full sequential injection. Which is another option! Its basically LPG but has injections etc, its far better than mixer rings!
One thing you will have to think about a little is timing. LPG runs better on far more advance than petrol, you can get modules that advance the timing when running on LPG.
What normally happens is you start on petrol, then flick over to LPG when the engine is warm. Some people can start on LPG apparently but its not the norm?
If you want to keep your carburettors but want to run well on both LPG & Petrol, then you can get something called megajolt. Which uses some coil packs and is an Electronic Distributorless Ignition System! Its neat so you can run two different spark maps (like a fuel map on electronic fuel injection!). One for petrol and one for LPG.
Now thats about as far as my knowledge goes... I don't have a BLOS carburettor and nor do I have megajolt. But megasquirt+EDIS and LPG is something I have been looking into for a while as it will make running my 3.5L RRC a lot nicer.
There are people on here with far far more knowledge than I and will add and correct anything I've said.
Anyone want to rip any of that apart, drag me down the street for heresy and misinformation? Correct me please where needed!
