Marks right no difference in smoke.... Mark ever wonder why the price of chicken keeps costing more and more

 

Ed, to answer your question - there's no real best system. It's more about the expertise of the guy who installs it and sets it up. I've had 3 LPG cars now, a BMW 330i, a Cherokee 4.0 and a P38 Range Rover. They all saved me money.

For anyone still reading, the difference between Petrol and LPG prices in the UK is huge. I pay between 47.9 (ASDA/Walmart) and 59.9 pence per litre for LPG but Petrol is about £1.20 per litre. Call it a 50% saving in the cost of the fuel per litre.

However, other posters are right - there's less calorific value in LPG per unit volume. If we bought fuel by weight, I don't think there would be anything like the same difference but we don't so... there's not a lot we can do about that.

Anyway, the 10% drop in energy available per litre means that you get 10% less fuel economy if you're measuring miles/gallong or miles/litre. That's because the LPG system will pump in 10% more LPG to make up the difference in power. If you've got an LPG converted car with a noticeable loss in power, it isn't set up properly. There's no reason for a modern multipoint system to lose out that way.

So the fuel saving should be around 40% in terms of cost per mile. Believe me, it makes a difference. On the BMW I was able to thrash a 155mph car for under 10 pence per mile in fuel. On the Range Rover, I'm able to buy and run a thirsty old 4.6 V8 without going bankrupt everytime I overtake a snail. In terms of payback, it depends how much you save per mile (big thirsty engines score here) and how many miles per year you cover. I've never driven a 2.5 but if you're likely to hanker for a 4.0 anytime soon I'd buy that first and then convert it instead. The last time I worked it out I would need to cover roughly 10k in for it to make sense, but once you've done the conversion the feeling of freedom you get knowing that filling the tank is likely to cost £30 instead of £70 is fantastic.

Converting a Cherokee is a bit more of a challenge because there's no spare wheel well. Most converted cars have a round tank in the spare wheel well and you keep your boot space. You can, if you want, put a vertical tank in the space that the spare goes in the cherokee but it's more expensive (it's not a common type of tank) and not particularly large. If you're going to use the boot for the tank, it's usually cheaper to put a big cylinder tank in and get more range.

The other option on tanks is to buy the Cherokee specific conversion tank from Tinley Tech that reduces your petrol capacity to 39litres and gives you an LPG tank with about 54 litres of useable volume. Seeing as the stock tank is about 75 litres this works out OK although once you have LPG you'll fill up as soon as the LPG tank is empty so your realistic range falls to about 180 miles unless you're a saint using cruise control at 65.

 

Thanks, Morat. That's a very informative post.

I'm wondering if the gutlessness that some of us have seen is due to trying to convert old school carbureted cars, instead of computerized and injected cars.

Any thoughts on that?

 

Wow, sorry for the thread necro and for missing the question.

The reason for loss of power in carburetted cars is because they don't use injectors but a mixer which is introduced upstream of the throttle body or carburetor. You can size them pretty large but they're never as smooth flowing as a straight pipe.
Here's an example http://www.lgc.hk/Products1025.html (not a recommendation!) which has a decent description...