Converting to LPG

How the system works

The tank is filled with the fuel in a liquid state under pressure and passes from the fuel tank to a fuel filter at the front of the car via a fuel pipe laid under the car, out of sight. The liquid passes through this filter and then into a vaporiser. It is here that the liquid turns to a gas. Vaporisation has a cooling effect, so the vaporiser is fed hot water from pipes connected to the engine cooling system to prevent this.

An additional plate is sandwiched between the carburettor casing and the U bend air intakes and the gas is routed from the vaporiser to these plates via rubber hosing. Once into the carburettors, you have the traditional "suck, squeeze, bang, blow" associated with a 4 stroke engine.

LPG is a slow burning fuel and so some specialists will advise that you should retard ignition and upgrade HT leads and spark plugs for best starting and running.

The conversion of my Rover SD1 3500SE auto

If you are considering a conversion to dual fuel, it is essential to first assess the state of your engine. If your engine is worn out, there is no point converting. My car had covered 194,000 miles when the conversion was done, and the cylinder heads were thought to be in good condition. The camshaft, followers, oil pump and timing chain had however been replaced six months earlier. The ignition side of things is critical to running your SD1 on LPG as the gas needs a bigger spark to ignite and burns more slowly than petrol. You must have a "good vacuum in your dizzy" and "big bangs in your cylinders" for the engine to work efficiently. It was necessary for me to replace the worn out distributor, fit Magnacor leads and Bosch spark plugs.

Day One: Arrived bright and early at RPi Engineering, Norfolk. Appearances can be deceptive and their ramshackle collection of outbuildings hid a fully equipped garage. First job was to weld the tank support to the boot floor, then secure the tank to the support using a pair of smart metal braces. The tank was located immediately behind the rear seat but some models of the fuel tanks will fit in the "false floor" where the spare wheel lives. Next job was to drill a hole under the rear bumper and to attach the filler bracket to the rear valance. The filler cap was attached to the tank via a filling pipe. In the afternoon, the fuel filter and the vaporizer were bolted to the nearside inner wing.

Day Two: Not so productive. The morning was spent moving the tank backwards, as it had been located too close to the back seat. The petrol over-ride cut-off switch was attached to the bulkhead and the petrol fuel pipe redirected via this switch and then onto the filter beneath the carburettors. This prevents the car from running on both petrol and gas - the switch prevents petrol reaching the carbs when the gas is on. The afternoon was spent wiring the tank, the filter, the over-ride switch, solenoid and vaporiser to the dual fuel switch I'd fitted in the centre console of the dashboard. RPi mechanics did most of this work, as electrics are not my forte. When they had done the wiring, I tidied it up.

Day Three: In the morning, the carburettor sandwich plates were bolted to the carburettors and then we laid out and attached the pipe that feeds the fuel from the tank in the boot to the vaporiser under the bonnet. Job done, lets go for a spin...

Filling up

The process of filling up with LPG is a quickly acquired skill. In the UK, there are two kinds of filler nozzle. BP use a screw type clamp, whilst Shell and some independent suppliers appear to favour the "bayonet". Both are quick and easy to use, but a garage forecourt will only usually give you a 30 second window to attach the fuel filler to your car. The gas flows at around the same speed as petrol so fill up times are comparable.

Reflections

Without doubt, the system has proved its worth in terms of both reliability and economy. The two main concessions that I have had to make is to both the MPG and range of the car compared to a tank of petrol. LPG has a lower calorific value than petrol so MPG is about 5% less. Allied to a smaller tank (48 litres vs. 65 litres) the cars range is less too. However, because the cost of LPG is so much lower than petrol (less than half currently) it still works out much more cost effective to run on LPG than petrol.

Post Script (16th October 2005)

Since converting to LPG over 5 years ago now, I feel that I can report honestly and with sufficient knowledge to give meaningful feedback. LPG has saved me a considerable sum at the forecourt. I know that I can run a 3.5 litre V8 for the same money as a 1.1 litre Rover Metro on petrol because I do..! As I type, petrol costs 0.979 pence per litre and LPG is only 0.429 pence a litre so I'm still saving 55p a litre at the pumps . Even concerns about the availability of LPG have proved unfounded. I have access to LPG in my home village and at work (twenty miles away). Even longer distance trips are not a problem. LPG is available, for example, at the first big garage forecourt that you come across in Dover, so a Booze Cruise can be made even more cheaply. For a couple of quid, you can buy a map that pinpoints every LPG station in the UK - it's even updated every year.

It's not all been good news though. After about 3 years, the original vaporiser was proving troublesome and was replaced with something that my local LPG installer was more familiar with. LPG has now become so popular that I sometimes have to queue to fill up. Outrageous..! There are some concerns that the duty on LPG (frozen for many years) will will be progressively increased so that it could become as expensive as petrol. That's a long way off, however, and seems to me as unlikely.

I converted Bob to run on LPG in late August 2000. The work was carried out at RPi Engineering Ltd and took three days to complete. I did much of the work myself under the supervision of their mechanic Geoff. At the point of writing, I have done over 40,000 trouble-free miles on gas and I reckon that the conversion costs have already been recouped by the savings against the costs of petrol.

Below is an edited version of the article that I wrote for the November/December (issue 57) Rover SD1 Club magazine which I have updated where appropriate (as at October 2005).

Running your SD1 on a shoestring!

Introduction

How much does it cost to fill your SD1 petrol tank these days? £60? How often does it need filling? If you use your SD1 every day and cover average miles, probably every fortnight. But what if you could run your SD1 for less than half the price of unleaded petrol? And what if your fuel was a higher octane rating than the old 5 star petrol? Why then, you would be running on Liquid Petroleum Gas.

Regular readers will recall that I was toying with the idea of converting my car to dual fuel in the May/June issue of the magazine. My fuel bills were in excess of £100 a month, so I decided it was time to either convert or sell. Retro-fitting LPG kits is common on gas-guzzlers such as Jaguars and Range Rovers, and you can buy LPG cars brand new from manufacturers like Citroen, Vauxhall and Ford. Although my car isn't the first LPG SD1, it is the first to be documented for the club.

There are many benefits to running your SD1 on LPG, mainly environmental. As it's a gas when entering the engine combustion chamber it mixes more readily than petrol with the air and so burns much more cleanly. This gives better emissions, less wear in the cylinders, much slower degradation of oil (and therefore less wear and tear to the engine generally), and of course there are the benefits to your wallet. My gas tank holds around 48 litres, costs a mere £18 to fill from completely empty and I get an average 20mpg which is comparable to (but worse than) petrol. An SD1 petrol tank holds 65 litres but costs significantly more to fill up. The drawbacks of the conversion are the initial costs, the loss of boot space and the lack of garages selling LPG. It is not, therefore, a solution for everyone (especially those owners for whom originality and/or boot space is a premium).